CHAPTER V
COLEOPTERA—OR BEETLES
ORDER V. COLEOPTERA.
_Apparently wingless Insects when at rest, but really with four wings; the elytra, or anterior pair, shell-like, reposing on the back of the body and fitted together accurately along the middle by a straight suture; the posterior pair membranous, folded together under the elytra. Mouth with mandibles; lower lip not divided along the middle. Metamorphosis great and very abrupt; the larva being a grub or maggot, which changes to a pupa (usually soft) in which the external structure of the perfect Insect is conspicuous._
Coleoptera—or Beetles—are chiefly distinguished from other Insects by the solidity of their external integument, and by the peculiar nature of the first pair of their alar organs, which do not serve as instruments of flight, but as shells for protecting the upper face of the after-body, which, unlike the other parts, remains as a rule soft and membranous. These modifications of structure, though apparently slight, must be really extremely advantageous, for beetles are the predominant Order of Insects in the existing epoch. They depart from most other Insects in being less aerial in their habits; therefore, notwithstanding their enormous numbers, they do not meet the eye so frequently as flies, bees, or butterflies. The parts of the hard outer skeleton are beautifully fitted together, and as their modifications are easily appreciated they offer as fascinating a subject for study as do the skeletons of Vertebrata. The habits of beetles are so extremely varied that it is but little exaggeration to say that Coleoptera are to be found everywhere, when looked for. The number of species at present known is probably about 150,000. Of these somewhere about 3300 have been found in Britain.
{185}[Illustration: Fig. 83—Under-surface of a beetle, _Harpalus caliginosus_; legs and antenna of one side, and some parts of the mouth removed. A, antenna; B, mandible; C, labrum; D, ligula; E, paraglossa; F, labial palp; G, inner lobe of maxilla; H, outer lobe (palpiform) of maxilla; I, maxillary palp; K, mentum; L, gena; M, gula; N, buccal fissure; V, plates of ventral segments. 1, Prosternum; 2, prosternal episternum; 3, prosternal epimeron; 4, anterior and middle coxal cavities; 5, inflexed side of pronotum; 6, mesosternum; 7, mesosternal episternum; 8, mesosternal epimeron; 9, metasternum; 10, posterior division of metasternum or ante-coxal piece; 11, metasternal episternum; 12, metasternal epimeron; 13, epipleuron or inflexed margin of elytron; 14, ventral or ambulatory setae; 15, trochanter; 16, posterior coxa; 17, femur; 18, tibia; 19, tarsus. (Modified from Leconte and Horn.)]
The structure of the hard parts of the skeleton is of importance, as the classification of this enormous number of species is entirely based thereon; it will be readily understood from the accompanying diagram (Fig. 83). The general proportions of the chief parts of the body call for a few remarks. The prothorax is remarkably free, and is therefore capable of a much greater amount of movement independent of the after-body than it is in other Insects. The mesothorax is, on the other hand, much reduced; its chief function in the higher forms is to support the elytra, and to help to keep them together by means of its scutellum. The metathorax, on the contrary, is largely developed, except in the rather numerous forms that are entirely deprived of powers of flight. The composition of the abdomen has been a subject of great difference of opinion. Its upper surface is usually entirely covered by the elytra; the parts visible on the lower surface are called ventral segments, and are usually five in number. Although these five plates may constitute all that is superficially visible of the abdomen, yet if the elytra are taken off it is found that a larger number of segments—usually seven or eight—are visible on the dorsum. This seeming discrepancy of number between the {186}dorsal and ventral plates is due to two facts; 1, that the hind coxae have a great and complex development, so that they conceal the true base of the venter, which, moreover, remains membranous to a greater or less extent, and thus allows much mobility, and at the same time a very accurate coadaptation between the hard parts of the venter and the metasternum[76]; 2, that the terminal segments are withdrawn into the interior of the body, and are correspondingly much modified, the modification being greater in the case of the ventral than in that of the dorsal plates. The anatomy of the parts of the abdomen that are not externally visible has not been adequately studied by coleopterists, but Verhoeff has inaugurated a careful study of the comparative anatomy of the terminal segments[77]; unfortunately, however, he has not so thoroughly studied the modifications at the base, and as it is not clear that these are so uniform as he has taken for granted, it is possible that his numbering of the segments may have to be in some cases modified. The retracted plates or segments are so intimately connected with the internal copulatory organs that it is no easy matter to interpret them. For the nomenclature of these parts we must refer the student to Verhoeff's later works. He considers the abdomen as composed of ten segments, the dorsal plates being demonstrable, while the tenth ventral plate is usually absent. The anal orifice is placed immediately beneath the tenth dorsal plate, and above the genital orifice, which lies behind and above the ninth ventral plate. Peytoureau admits a diversity in both the number of segments and the position of the orifice. These studies in comparative anatomy are surrounded with difficulties, and no morphological conclusions based on them can be considered as final until they have been confirmed by observation of the development of the parts.
The elytra—or wing-cases—frequently have a remarkable sculpture, the use of which is unknown. According to Hofbauer there are between the outer and inner layers, glands secreting a {187}fluid that reaches the surface through small pores. Hicks supposed that he detected nerve cells. Meinert is of opinion that the elytra correspond to the tegulæ of Hymenoptera rather than to the wings of other Insects, but the little evidence that exists is not favourable to this view. The two elytra are usually, in repose, very perfectly fitted together by a complete coadaptation along the middle of the body, so that it is difficult to separate them; this line of junction is called the suture. There are forms in which the coadaptation is quite imperfect (Malacodermidae) and some in which it does not exist at all (_Meloë_). The wings proper of beetles correspond to the posterior pair in other Insects, and are much more irregular in nervuration than those of most other Insects, correlative, it is supposed, with the folding they are subjected to in order to get them beneath the wing-cases. There are large numbers of species, genera, and groups of genera, all the members of which have the wings so much reduced in size as to be quite useless for purposes of flight. These forms are called apterous, though they are not really so, for the elytra (which are really the anterior wings) are present, and even the posterior wings are not truly absent in these cases, though they are sometimes so extremely rudimentary as to elude all but the most careful observation. The number of forms in which the elytra are absent is extremely small; this condition occurs only in the female sex; it is usually confined to cases in which the female is larva-like in form; but in the extraordinary Mediterranean Lamellicorn genus, _Pachypus_, the females are destitute of wings and elytra, though the anterior parts of the body are normally formed: these individuals live underground and rarely or never emerge. When the wings are absent the elytra are frequently soldered; that is to say, united together along the suture by some sort of secondary exudation; this union occurs in every degree of firmness, and appears to be variable in the individuals of one species; probably in accordance with the age of the individual. In most beetles the elytra are not only themselves closely connected, but are also very accurately coadapted with the sides of the body, except at the tip. Sometimes a coadaptation occurs between the tips of the elytra and the body, but not at the tip of the latter. In such cases one or more dorsal plates are left exposed: the last of such exposed dorsal plates is termed pygidium; a similar plate anterior to the pygidium is called propygidium.
{188}LARVAE.—Owing to the difficulty of rearing Coleoptera, less is perhaps known of their life-histories than of those of other Insects. They exhibit, however, extreme diversity correlative with the great specialisation of so many beetles to particular kinds of life. Most beetles must have exactly the right conditions to live in. The larvae of many forms are known. They are composed of a head, three thoracic segments (usually very distinct), and a number of abdominal segments varying from eight to ten. Coleopterous larvae are usually described as having nine abdominal segments; and it is but rarely that ten can be readily detected; they are, however, visible in various forms, as is the case in the form figured (Fig. 84). A great many of them possess a peculiar pseudopod at the underside of the body near or at the extremity; it can in many cases be entirely retracted into the body, and is generally described as being the protruded termination of the alimentary canal. Inspection of a series of larvae shows that it represents a body segment: it is sometimes armed with hooks. Three pairs of small thoracic legs are often present, but are very often completely absent. These thoracic legs may be present in the young larva, but not in the older (_Bruchus_). The usual number of spiracles is nine pairs, one prothoracic, eight abdominal; but this is subject to many exceptions, and mesothoracic and metathoracic stigmata are occasionally found. The figures we give in the following pages will enable the student to form some idea of the variety of form exhibited by beetle larvae.
[Illustration: Fig. 84—Larva of a beetle, Family Cerambycidae (? _Aromia moschata_). The first spiracle is placed just at the hind margin of the large prothoracic segment. (From La Massane.)]
Pupation usually takes place in a cavity in the earth, or near the feeding-place, but a great many species form a cocoon, composed either of fragments of earth or of wood, and slightly cemented together. A few suspend themselves by the tail after the manner of butterfly caterpillars (Cassididae, Coccinellidae). The pupae are usually extremely soft, their appendages not being fastened to the body. But some pupae (Staphylinides) are truly obtected, having a hard shell and the rudimentary appendages fastened by exudation to the body, like Lepidopterous pupae, and others (Coccinellidae) are intermediate {189}between this state and the normal soft pupa. The pupal state lasts but a short time, from one to three weeks being the usual period. The perfect Insect is at first soft and almost colourless, and it is often some days before it attains its complete coloration and hardness.
CLASSIFICATION.—Owing to the hardness of the skeleton, beetles shrivel but little after death, so that the form and relations of the various sclerites can usually be detected with ease. These sclerites seem to be remarkably constant (except in the case of sexual distinctions) within the limits of each species, and are very useful for the formation of genera and groups of genera; but they vary so much outside the limits mentioned that it is very difficult to make use of them for defining the larger groups. Hence it is not easy to frame accurate definitions of the families, and still less so to arrange these families in more comprehensive series. The natural difficulty has been much increased by the habit coleopterists have of framing their definitions on what is visible without the aid of dissection. Nevertheless considerable progress has been made. We are obliged at present to adopt upwards of eighty families; and we are able to distinguish on positive characters five series; this leaves a large number of forms still unclassified, and these we have here associated as a sixth series, which we have called Coleoptera Polymorpha. This series corresponds with the two series called in books Clavicornia and Serricornia. As it is admitted to be impossible to define these two series, we think it much better to act accordingly, and to establish for the present a great group that can only be characterised by the fact that its members do not belong to any of the other five series. No doubt a larger knowledge of development, coupled with the advance of comparative anatomy, will ultimately bring about a better state of affairs. The Strepsiptera, with one family Stylopidae, are only provisionally included among the Coleoptera. These six series are fairly equal as regards extent. Though the Polymorpha includes the larger number of forms, yet a large part of them belong to four great families (Staphylinidae, Buprestidae, Elateridae, Malacodermidae), which are easily recognisable, so that the number of unmanageable forms is not really great. Indeed, an acquaintance with the external anatomy of two or three dozen species, selected as typical, would enable a student to classify {190}with tolerable certainty the vast majority of species that he would subsequently meet with.
Series 1. _Lamellicornia._—Antennae with the terminal joints leaf-like (or broader than the others, if not actually leaf-like), and capable of separation and of accurate apposition. Tarsi five-jointed.
Series 2. _Adephaga_—(_Caraboidea_ of some authors).—Antennae never lamelliform, thin at the end; all the tarsi five-jointed, with the fourth joint quite distinct. Maxillae highly developed, with the outer lobe slender and divided into two segments so as to be palpiform. Abdomen with six (or more) ventral segments visible.
Series 3. _Polymorpha._—Antennae frequently with either a club, _i.e._ the distal joints broader [Clavicorn series of authors], or the joints from the third onwards more or less saw-like, the serrations being on the inner face [Serricorn series of authors]; but these and all the other characters, including the number of joints in the feet, very variable.
Series 4. _Heteromera._—Front and middle tarsi five-jointed, hind tarsi four-jointed. Other characters very variable.
Series 5. _Phytophaga._—Tarsi four-jointed [apparently], but with a small additional joint at the base of the fourth joint: sole usually densely pubescent [sometimes the feet are bare beneath or bristly, and occasionally the small joint at the base of the fourth joint is more distinct].
Series 6. _Rhynchophora._—Head prolonged in front to form a beak; gula indistinguishable. [Palpi usually not evident.] Tarsi four-jointed [apparently], but with a very minute additional joint at the extreme base of the fourth joint.
_Strepsiptera_ (see p. 298).
The first and second series, with much of the third, form the Pentamera, the fifth and sixth the Tetramera [or Pseudotetramera[78]]. The term Isomera was applied by Leconte and Horn to a combination of series 1, 2, 3, and 5.
SERIES 1. LAMELLICORNIA.
_Tarsi five-jointed; antennae with the terminal joints (usually three, sometimes more), broader on one side, so as to form a peculiar club, the leaves of which are movable, and in repose are more or less perfectly coadapted so as to have the appearance of being but one piece._
This series includes three families, Passalidae, Lucanidae, and Scarabaeidae; the latter includes an enormous majority of the species, and in them the structure of the antennae characteristic of the series is well developed; but in the other two families {191}the form of the antennae is not so widely different from that of other Coleoptera. The larvae live on decaying vegetable matter, roots or dung. They have three pairs of legs, and are thick clumsy grubs with curved bodies, the last two segments being of larger size than usual. Many of them possess organs of stridulation, and the structure of their spiracles is very peculiar, each one being more or less completely surrounded by a chitinous plate. The spiracles usually form a system entirely closed, except at the moment when the skin is shed and the tracheal exuviae are detached. Meinert[79] considers these spiracles to be organs of hearing. The life of the larvae is passed underground or in the decaying wood on which the Insect feeds.
[Illustration: Fig. 85.—Antennae of Lamellicorns. 1, _Neleus interruptus_; 2, _Lucanus cervus_ ♂; 3, _Phanaeus splendidulus_ ♀; 4, _Phileurus didymus_ ♀; 5, _Polyphylla fullo_ ♂.]
Most of the members of this series are remarkable on account of the great concentration of the nerve-centres. This is extreme in _Rhizotrogus_, where there are only two great ganglia, viz. the supra-oesophageal and a great ganglion situate in the thorax, and consisting of the conjoined infra-oesophageal, thoracic, and abdominal ganglia. According to Brandt[80] there are several distinct forms of concentration in the series; the Lucanidae only participate in it to the extent that the perfect Insects exhibit fewer ganglia than the larvae; the latter possess two cephalic, three thoracic, and eight abdominal ganglia, while the perfect Insect has the abdominal ganglia reduced in number to six, and {192}they are placed
## partially in the thorax. The diminution in number takes place in this case
by the amalgamation of the first two abdominal with the last thoracic ganglia.
[Illustration: Fig. 86—View of one side of meso- and metathorax of a Passalid larva from Borneo showing the stridulating organs. _a_, _b_, Portions of the metathorax; _c_, coxa of 2nd leg; _d_, striate or stridulating area thereon; _e_, basal part of femur of middle leg; _f_, hairs with chitinous process at base of each; _g_, the diminutive 3rd leg modified for scratching the striated area. × 20.]
FAM. 1. PASSALIDAE.—_Labrum large, mobile; mentum deeply cut out in the middle for the accommodation of the ligula; the lamellae of the antenna brought together by the curling up of the antenna. The elytra entirely cover the dorsal surface of the abdomen._ There are four or five hundred species of this family known; they are usually shining-black, unattractive beetles, of large size, and are abundant in the decaying wood of tropical forests. They are quite absent from Europe, and there is only one species in the United States of North America. The larvae are very interesting, from the fact that they appear to have only four legs. This arises from the posterior pair being present only as very short processes, the function of which is to scrape striated areas on the preceding pair of legs and so produce sound. In the species figured (Fig. 86) this short leg is a paw-like structure, bearing several hard digits; but in other species it is more simple, and without the digits. The perfect Insect has no sound-producing organs, and it is very remarkable therefore to find the larvae {193}provided with highly-developed stridulatory structures. No auditory organ is known, unless the peculiar spiracles be such.
[Illustration: Fig. 87—Head and prothorax of forms of the male of a stag-beetle; _Homocoderus mellyi_ (Africa). A, Large, B, intermediate, C, small forms. (From a photograph by R. Oberthür.)]
FAM. 2. LUCANIDAE (_Stag-beetles_).—_Labrum indistinct, fixed; mentum not excised; antennae not curled in repose, with but little coadaptation of the terminal joints; the elytra entirely cover the dorsal surface of the abdomen._ The Stag-beetles are well known on account of the extraordinary development of the mandibles in the male sex, these organs being in some cases nearly as long as the whole of the rest of the Insect, and armed with projections or teeth that give the Insects a most formidable appearance. So far as we have been able to discover, these structures are put to very little use, and in many cases are not capable of being of service even as weapons of offence. The males are usually very much larger than the females, and are remarkable on account of the great variation in the stature of different individuals of the same species; correlative with these distinctions of individual size we find extreme differences in the development of the head and mandibles. Moreover, the small male specimens exhibit not merely reductions in the size of the mandibles, but also show considerable differences in the form of these parts, due, in some cases, apparently to the fact that only when a certain length of the mandible is attained is there any development of certain of the minor projections: in other cases it is not possible to adopt this view, as the small mandibles bear as many projections as the large forms do, or even more. In each species these variations fall, in the majority of cases, into distinct states, so that entomologists describe them as "forms," the largest developments being called teleodont, the smallest priodont; the terms mesodont and amphiodont being applied to intermediate states. Leuthner, who has examined many specimens, states that in _Odontolabis sinensis_, no intermediates between the teleodont and mesodont forms occur, and as the {194}two forms are very different they are liable to be mistaken for distinct species.
There are at present between 500 and 600 species of stag-beetles known; the Indo-Malayan and Austro-Malayan regions being richest in them. Australia possesses many remarkable and aberrant forms. In the Ceratognathini—a group well represented in New Zealand as well as in Australia—the structure of the antennae is like that of the Scarabaeidae, rather than of the Lucanidae. The most aberrant form known is, however, our common _Sinodendron cylindricum_; this departs in numerous features from other Lucanidae, and instead of the mandibles of the male being more largely developed, there is a horn on the head; it is very doubtful whether this Insect should be allowed to remain in the family. Little is known of the habits and development of Lucanidæ, except in the case of three or four species that are common in Europe.
[Illustration: Fig. 88—_Sinodendron cylindricum._ A, Larva; B, pupa. New Forest.]
The common stag-beetle, _Lucanus cervus_, is our largest British beetle. The larva much resembles that of _Melolontha vulgaris_, but attains a larger size, and the anal aperture is placed longitudinally instead of transversely; it lives in decaying wood, or eats the roots of trees without being injurious; its life in this state lasts about four years; the pupal period is passed through rapidly, and the perfect Insect may remain for months underground before it becomes active; this occurs in June and July. This larva stridulates by scraping certain hard tubercular ridges on the third pair of legs, over a specially adapted rough area at the base of the second pair.
The Passalidae and Lucanidae are united by some authorities as a group called Pectinicornia; the term Lamellicornia being then confined to the Scarabaeidae. The Passalidae appear, however, to be really more nearly allied to the Scarabaeidae than to the Lucanidae.
FAM. 3. SCARABAEIDAE (_Chafers_).—_The leaflets of the antennae are well coadapted, and are susceptible of separation. The elytra {195}usually leave the pygidium uncovered. The number of visible ventral segments is usually six, or at the sides seven, not five, as in Lucanidae and Passalidae._ This is one of the most important families of Insects. About 13,000 species are already known; as some of them are highly remarkable creatures on account of the males being armed with horns, they are figured in many works on natural history. There is great variety of form, and the following five sub-families may be adopted, though authorities are by no means agreed as to the classification of this extensive family, which, moreover, be it remarked, is increasing by the discovery of about 300 new species every year.
Abdominal spiracles placed in a line on the connecting membranes, and entirely covered by the wing-cases (Laparosticti). Sub-fam. 1. COPRIDES.[81]
Abdominal spiracles placed almost in a line, but only the basal three on the connecting membranes; the terminal one usually not covered by the wing-cases. Sub-fam. 2. MELOLONTHIDES.
Abdominal spiracles placed in two lines, the basal three on the connecting membranes, the others on the ventral segments (Pleurosticti).
The claws of the tarsi unequal. Sub-fam. 3. RUTELIDES.
The claws of the tarsi equal; the front coxae transverse, but little prominent in the descending axis. Sub-fam. 4. DYNASTIDES.
The claws of the tarsi equal; the front coxae more prominent, shorter transversely. Sub-fam. 5. CETONIIDES.
i. The Coprides form an immense group of about 5000 species; they differ somewhat in habits from other Lamellicorns, inasmuch as most of them live on dung, or decaying animal matter; the sub-family connects with the Lucanidae, so far as superficial characters go, by means of two of its groups, Trogini and Nicagini, the latter being very near to the Ceratognathini in Lucanidae. So little is known as to the morphology and development of these groups that it is not possible to pronounce an opinion as to the validity of this apparent alliance. _Trox_ stridulates by rubbing two raised lines on the penultimate dorsal segment across two striate ribs on the inner face of the elytra; _Geotrupes_, on the other hand, produces an audible sound by rubbing together a file on the posterior coxa and a fine ridge on the contiguous ventral segment. The larva in this genus has a different organ {196}for stridulation from the imago; it is placed on the second and third pairs of legs, the latter pair being much reduced in size.
The most interesting division of the Coprides is the group Scarabaeini. No member of this group inhabits the British islands, but in Southern Europe, and in still warmer lands, these Insects are well known from the curious habit many of the species have of rolling about balls of dung and earth. The long hind legs are chiefly used for this purpose, and it is on the peculiar structure of these limbs that the group has been established. Many of the stone Scarabaei found in Egyptian tombs represent some kind of Scarabaeini, and it has been said that the ancient Egyptians looked on these Insects as sacred because of their movements. These must certainly appear very strange to those who see them and are unacquainted with their object. It is stated that the dwellers in the valley of the Nile thought the actions of these Insects, when rolling their balls, were typical of the planetary and lunar revolutions; and that the sudden appearance of the beetles after a period of complete absence was emblematic of a future life. Many accounts have been given of the habits of members of this group, but according to Fabre all are more or less erroneous; and he has described the habits and life-history of _Scarabaeus sacer_ (Fig. 89), as observed by him in Southern France. These Insects act the part of scavengers by breaking up and burying the droppings of cattle and other animals. The female _Scarabaeus_ detaches a portion of the dung and forms it into a ball, sometimes as large as the fist; this it rolls along by means of its hind legs, by pushing when necessary with its broad head, or by walking backwards and dragging the ball with its front legs. The strength and patience displayed by the creature in the execution of this task are admirable. Frequently the owner of this small spherical property is joined, so Fabre informs us, by a friend, who is usually of the same sex and assists her in pushing along the ball till a suitable place is reached. When this is attained, the owner commences to excavate a chamber for the reception of the ball; sometimes the false friend takes advantage of the opportunity thus offered and carries off the ball for her own use. Should no disappointment of this sort occur, the _Scarabaeus_ accomplishes the burying of the ball in its subterranean chamber, and accompanies it for the purpose of devouring it; the feast is continued without intermission till the food is entirely {197}exhausted, when the _Scarabaeus_ seeks a fresh store of provender to be treated in a similar manner. According to M. Fabre's account these events occur in the spring of the year, and when the hot weather sets in the _Scarabaeus_ passes through a period of quiescence, emerging again in the autumn to recommence its labours, which are now, however, directed immediately to the continuance of the species; a larger subterranean chamber is formed, and to this retreat the beetle carries dung till it has accumulated a mass of the size of a moderate apple; this material is carefully arranged, previous to the laying of the egg, in such a manner that the grub to be hatched from the egg shall find the softest and most nutritive portions close to it, while the coarser and more innutritious parts are arranged so as to be reached by the grub only after it has acquired some strength; lastly, a still more delicate and nutritive paste is prepared by the mother beetle for a first meal for the newly-hatched grub, by some of the food being submitted to a partial digestion in her organs; finally, the egg is deposited in the selected spot, and the chamber closed. Certain of the Coprides exhibit, according to Fabre, some extremely exceptional features in their life-histories. The mother, instead of dying after oviposition, survives, and sees the growth of her young to the perfect state, and then produces another generation. No similar case can be pointed out in Insects, except in the Social kinds; but from these the Coprides observed by Fabre differ profoundly, inasmuch as the number of eggs produced by the mother is extremely small; _Copris hispanus_, for instance, producing in each of its acts of oviposition only one, two, or three eggs.
[Illustration: Fig. 89—_Scarabaeus sacer._ Portugal.]
{198}ii. The Melolonthides are probably almost as numerous as the Coprides, some 4000 species being already known. The larvae are believed to feed chiefly on roots. _Melolontha vulgaris_, the common cockchafer, is very abundant in some parts of Europe, and owing to this and to the great damage it causes, has attracted much attention. The memoir by Straus-Durckheim[82] on its anatomy is one of the classical works of Entomology. This Insect is so injurious in some parts of France that money is paid by the local authorities for its destruction. M. Reiset informs us that under this arrangement 867,173,000 perfect cockchafers, and 647,000,000 larvae were destroyed in the Seine-inférieure in the four years from the middle of 1866 to 1870. Unlike the Coprides, the larval life in Melolonthides is prolonged, and that of the imago is of brief duration. In Central Europe the life-cycle of the individual in _M. vulgaris_ occupies three years, though in dry periods it may be extended to four years. In Scandinavia the time occupied by the development appears to be usually five years. The fertile female enters the ground and deposits its eggs in two or three successive batches of about fifteen each. The eggs swell as the development of the embryo progresses; the larva emerges about five weeks after the eggs have been deposited, and is of relatively large size. When young the larvae can straighten themselves out and crawl, but when older they lose this power, and when above ground rest helplessly on their sides. In the winter they descend deeply into the earth to protect themselves from frost. The pupa state lasts only a few days, but after the final transformation the perfect Insect may remain motionless for as much as eight months underground before commencing its active life in the air.[83] In the perfect state the Insect is sometimes injurious from the large quantity of foliage it destroys. Schiödte[84] considered that these larvae (and those of numerous other Scarabaeidae) stridulate by rubbing certain projections on the stipes of the maxilla against the under-surface of the mandible. These surfaces appear, however, but little adapted for the purpose of producing sound.
iii. The Rutelides number about 1500 species; there are many {199}Insects of brilliant metallic colours amongst them, but very little is known as to their life-histories. The larvae are very much like those of Melolonthides.
iv. The Dynastides are the smallest division in number of species, there being scarcely 1000 known; but amongst them we find in the genera _Dynastes_ and _Megasoma_ some of the largest of existing Insects. The horns and projections on the heads and prothoraces of some of the males of these Insects are truly extraordinary, and it does not appear possible to explain their existence by any use they are to their possessors. These structures are but little used for fighting. Baron von Hügel informs the writer that in Java he has observed large numbers of _Xylotrupes gideon_; he noticed that the males sometimes carry the females by the aid of their horns; but this must be an exceptional case, for the shape of these instruments, in the majority of Dynastides, would not allow of their being put to this use. The development of these horns varies greatly in most of the species, but he did not find that the females exhibited any preference for the highly armed males. The fact that the males are very much larger than the females, and that the armature is usually confined to them, suggests, however, that some sexual reason exists for these remarkable projections. Many Dynastides possess organs of stridulation, consisting of lines of sculpture placed so as to form one or two bands on the middle of the propygidium, and brought into play by being rubbed by the extremities of the wing-cases. This apparatus is of a less perfect nature than the structures for the same purpose found in numerous other beetles. We have no member of this sub-family in Britain, and there are scarcely a dozen in all Europe. Decaying vegetable matter is believed to be the nutriment of Dynastides. The European _Oryctes nasicornis_ is sometimes found in numbers in spent tan. The growth and development of the individual is believed to be but slow.
v. The Cetoniides are renowned for the beauty of their colours and the elegance of their forms; hence they are a favourite group, and about 1600 species have been catalogued. They are specially fond of warm regions, but it is a peculiarity of the sub-family that a large majority of the species are found in the Old World; South America is inexplicably poor in these Insects, notwithstanding its extensive forests. In this sub-family the mode of flight is peculiar; the elytra do not extend down the {200}sides of the body, so that, if they are elevated a little, the wings can be protruded. This is the mode of flight adopted by most Cetoniides, but the members of the group Trichiini fly in the usual manner. In Britain we have only four kinds of Cetoniides; they are called Rose-chafers. The larvae of _C. floricola_ and some other species live in ants' nests made of vegetable refuse, and it is said that they eat the ants' progeny. Two North American species of _Euphoria_ have similar habits. The group Cremastochilini includes numerous peculiar Insects that apparently have still closer relations with ants. Most of them are very aberrant as well as rare forms, and it has been several times observed in North America that species of _Cremastochilus_ not only live in the nests of the ants, but are forcibly detained therein by the owners, who clearly derive some kind of satisfaction from the companionship of the beetles. The species of the genus _Lomaptera_ stridulate in a peculiar manner, by rubbing the edges of the hind femora over a striate area on the ventral segments.
SERIES II. ADEPHAGA OR CARABOIDEA.
_All the tarsi five-jointed; antennae filiform, or nearly so; mouth-parts highly developed, the outer lobe of the maxilla nearly always divided into a two-jointed palpus; supports of the labial palpi developed as joints of the palpi, and in some cases approximate at their bases. Abdomen with the exposed segments one more in number at the sides than along the middle, the number being usually five along the middle, six at each side._
This extensive series includes the tiger-beetles, ground-beetles, and true water-beetles; it consists of six families, and forms a natural assemblage. It is sometimes called Carnivora or Filicornia. The exceptions to the characters we have mentioned are but few. The supports of the labial palpi are frequently covered by the mentum, and then the palpi appear three-jointed; but when the joint-like palpiger is not covered these palps appear four-jointed. As a rule, approximation of these supports is indicative of high development. In some of the lower forms the trophi remain at a lower stage of development than is usual. This is especially the case with the genus _Amphizoa_, which forms of {201}itself the family Amphizoidae. The Bombardier-beetles make an exception as regards the abdominal structure, for in some of them no less than eight segments are visible, either along the middle line or at the sides of the venter. In Hydroporides (one of the divisions of Dytiscidae) the front and middle feet have each only four joints. Many naturalists unite the Gyrinidae with the Adephaga, and a few also associate with them the Paussidae and Rhysodidae; but we think it better at present to exclude all these, though we believe that both Paussidae and Rhysodidae will ultimately be assigned to the series. The larvae are usually very active, and have a higher development of the legs than is usual in this Order. Their tarsi possess two claws.
FAM. 4. CICINDELIDAE (_Tiger-beetles_).—_Clypeus extending laterally in front of the insertion of the antennae. Lower lip with the palpi usually greatly developed, but with the ligula and paraglossae very much reduced, often scarcely to be detected. Maxillae with the outer lobe forming a two-jointed palp,[85] the inner lobe elongate, furnished at the tip with a hook-like process, which is usually articulated by a joint with the lobe itself._ The tiger-beetles are very active Insects, running with extreme speed, and sometimes flying in a similar manner; they are all predaceous, and amongst the most voracious and fierce of the carnivorous beetles, so that they well deserve their name. Bates, speaking of the Amazonian _Megacephala_, says "their powers of running exceed anything I have ever observed in this style of Insect locomotion; they run in a serpentine course over the smooth sand, and when closely pursued by the hand they are apt to turn suddenly back and thus baffle the most practised hand and eye." He further says that the species he observed (being of diverse colours) agreed in colour with the general colours of the "locale they inhabit." The larvae of Cicindelidae live in deep burrows, sinking more or less vertically into the ground, and in these they take up a peculiar position, for which their shape is specially adapted; the head and prothorax are broad, the rest of the body slender, the fifth segment of the abdomen is furnished on the back with a pair of strong hooks; the ocelli on the sides of the head are very perfect. Supporting itself at the top of the burrow by means of these hooks and of its terminal tube, the larva blocks the mouth of the burrow with its large head and prothorax, and {202}in this position waits for its prey. This consists of Insects that may alight on the spot or run over it. When an Insect ventures within reach, the head of the larva is thrown back with a rapid jerk, the prey is seized by the long sharp mandibles, dragged to the bottom of the burrow and devoured. The burrows are often more than a foot deep, and are said to be excavated by the larva itself, which carries up the earth on the shovel-like upper surface of its head. The female tiger-beetle is endowed with powerful and elongate excavating instruments at the termination of the body, and it is probable that when placing the egg in the earth she facilitates the future operations of the larva by forming the outlines of the burrow. Extremely few larvae of Cicindelidae are known, but they all exhibit the type of structure mentioned above, and apparently have similar habits. Our little British _Cicindela_, most of which are so active on the wing, agree in these respects with the African species of _Manticora_, which are entirely apterous, and are the largest of the Cicindelidae. Péringuey found a breeding-ground of _M. tuberculata_ near Kimberley; the larvae were living in the usual Cicindelid manner; but the ground was so hard that he was not able to investigate the burrows, and there were but few Insects that could serve as food in the neighbourhood.
[Illustration: Fig. 90—_Cicindela hybrida._ Britain. A, larva (after Schiödte); B, imago, male.]
The Cicindelidae, although one of the smaller families of Coleoptera, now number about 1400 species; of these about one-half belong to the great genus _Cicindela_, to which our four British representatives of the Cicindelidae are all assigned. There is no general work of much consequence on this important family, and its classification is not thoroughly established.[86]
{203}[Illustration: Fig. 91—Mouth-parts of tiger-beetles. A, Profile of _Pogonostoma_ sp. (Madagascar): _a_, antenna; _b_, labial palp; _c_, maxillary palp; _d_, palpiform lobe of maxilla; _e_, mandible; _f_, labrum. B, Section of head of _Manticora maxillosa_ (South Africa): _a_, front of upper part of head-capsule; _b_, gula; _c_, tentorium; _d_, eye; _e_, labrum; _f_, left mandible; _g_, maxilla; _h_, maxillary palp; _i_, labial palp; _k_, support of this palp; _l_, labium.]
Tiger-beetles display considerable variety of structure, especially as regards the mouth, which exhibits very remarkable developments of the palpi and labrum (Fig. 91). The tiger-beetles, like most other Insects that capture living prey, do not consume their victims entire, but subsist chiefly on the juices they squeeze out of them; the hard and innutritious parts are rejected after the victim has been thoroughly lacerated and squeezed; the mouth forms both trap and press; the palpi spread out in order to facilitate the rapid engulfing of a victim, then close up under it and help to support it in the mouth; while the labrum above closes the cavity in the other direction. The mouth itself is a large cavity communicating very freely with the exterior, but so completely shut off from the following parts of the alimentary canal that it is difficult to find the orifice of communication; the labium being much modified to form the posterior wall. For the capture of the prey, always living but of various kinds, a mechanism with great holding power and capable of rapid
## action is required. The mouth of the terrestrial _Manticora_ (Fig. 91, B),
exhibits great strength; some of the chitinous parts are extremely thick, the mandibles are enormous, the palpi, however, are comparatively low in development. In the arboreal genus _Pogonostoma_ the palpary structures (Fig. 91, A) attain a development scarcely equalled elsewhere in the Insect world. The great majority of the Cicindelidae are inhabitants of the warmer, or of the tropical regions of the world, and very little is known as to their life-histories; they show great diversity in their modes of hunting their prey. Some are wingless; others are active on the wing; and of both of these divisions there are forms that are found only on trees or bushes. Some, it is believed, frequent only the mounds of Termites. The characteristic feature common {204}to all is great activity and excessive wariness. The genus _Pogonostoma_, to which we have already alluded, is confined to Madagascar, where the species are numerous, but are rare in collections on account of the difficulty of securing them. Raffray informs us that certain species frequent the trunks of trees, up which they run in a spiral manner on the least alarm. The only way he could obtain specimens was by the aid of an assistant; the two approached a tree very quietly from opposite sides, and when near it, made a rush, and joined hands as high up the trunk as they could, so as to embrace the tree, when the _Pogonostoma_ fell to the ground and was captured.
[Illustration: Fig. 92—_Leistus spinibarbis._ A, Larva (after Schiödte); B, imago. Britain.]
FAM. 5. CARABIDAE (_Ground-beetles_).—_Clypeus not extending laterally in front of the antennae. Maxillae with the outer lobe destitute of an articulated hook at the tip. Antennae covered (except the basal joints) with a minute pubescence. Hind legs not very different from the middle pair, formed for running, as usual in beetles._ This is one of the largest and most important of the families of Coleoptera, including as it does 12,000 or 13,000 described species. In this country Carabidae are nearly entirely terrestrial in habits, and are scarcely ever seen on the wing; many of the species indeed have merely rudimentary wings; in the tropics there are, however, many arboreal forms that take wing with more or less alertness. The larvae (Fig. 92, A) are usually elongate in form and run freely; they may be known by their tarsi ending in two claws, by the exserted, sharp, calliper-like mandibles, by the body ending in two processes (sometimes jointed) and a tube of varying length projecting backwards. The pupae usually have the hind pair of legs so arranged that the tips of the tarsi project behind, beyond the extremity of the {205}body. The Carabidae are carnivorous and predaceous both as larvae and perfect Insects; they attack living Insects, worms, or other small, soft creatures, but do not disdain dead specimens. Some species of _Carabus_, found in North Africa where snails abound, are specially formed for attacking these molluscs, having the head long and slender so that it can be thrust into the shell of the snail. A few species have been detected eating growing corn, and even the young seeds of some Umbelliferae; these belong chiefly to the genera _Harpalus_, _Zabrus_, and _Amara_. Some species of the abundant genera _Pterostichus_ and _Harpalus_, are said to be fond of ripe strawberries. The most anomalous forms of Carabidae are the Pseudomorphides, a sub-family almost peculiar to Australia, the members of which live under bark, and have but little resemblance to other Carabids owing to their compact forms and continuous outlines. The genus _Mormolyce_ is one of the wonders of the Insect world on account of the extraordinary shape of its members; the sides of the elytra form large crinkled expansions, and the head is unusually elongate. These Insects live on the underside of fallen trees in the Malay Archipelago and Peninsula; no reason whatever can be at present assigned for their remarkable shape.
There are a considerable number of blind members of this family: some of them live in caverns; these belong chiefly to the genus _Anophthalmus_, species of which have been detected in the caves of the Pyrenees, of Austria, and of North America. It has been shown that the optic nerves and lobes, as well as the external organs of vision, are entirely wanting in some of these cave Carabidae; the tactile setae have, however, a larger development than usual, and the Insects are as skilful in running as if they possessed eyes. _Anophthalmus_ is closely related to our British genus _Trechus_, the species of which are very much given to living in deep crevices in the earth, or under large stones, and have some of them very small eyes. In addition to these cavernicolous _Anophthalmus_, other blind Carabidae have been discovered during recent years in various parts of the world, where they live under great stones deeply embedded in the earth; these blind lapidicolous Carabidae are of extremely minute size and of most sluggish habits; the situations in which they are found suggest that many successive generations are probably passed under the same stone. Not a single specimen has ever been found above ground. The minute {206}Carabids of the genus _Aëpus_, that pass a large part of their lives under stones below high-water mark (emerging only when the tide uncovers them), on the borders of the English Channel and elsewhere, are very closely allied to these blind Insects, and have themselves only very small eyes, which, moreover, according to Hammond and Miall, are covered in larger part by a peculiar shield.[87] A few Carabidae, of the genera _Glyptus_ and _Orthogonius_, are believed to live in the nests of Termites. Savage found the larva of _G. sculptilis_ in the nests of _Termes bellicosus_; it has been described by Horn, and is said to bear so great a resemblance to young queens of the Termites as to have been mistaken for them.[88] Mr. Haviland found _Rhopalomelus angusticollis_ in Termites' nests in South Africa. Péringuey states that it emits a very strong and disagreeable odour. It is probable that it preys on the Termites, and this also is believed to be the habit of the Ceylonese _Helluodes taprobanae_. Some species of the Mediterranean genus _Siagona_ stridulate by means of a file on the under surface of the prothorax, rubbed by a striate area, adapted in form, on the anterior femora.
A valuable memoir on the classification of this important family is due to the late Dr. G. H. Horn;[89] he arranges Carabidae in three sub-families; we think it necessary to add a fourth for _Mormolyce_:
1. Middle coxal cavities enclosed externally by the junction of the meso- and meta-sternum; neither epimeron nor episternum attaining the cavity.
Head beneath, with a deep groove on each side near the eye for the reception of the antennae or a part thereof. Sub-fam. 3. Pseudomorphides.
Head without antennal grooves. Sub-fam. 2. Harpalides.
2. Middle coxal cavities attained on the outside by the tips of the episterna and epimera. Sub-fam. 4. Mormolycides.
3. Middle coxal cavities attained on the outside by the tips of the epimera, but not by those of the episterna. Sub-fam. 1. Carabides.
These four sub-families are of extremely different extent and nature. The Harpalides are the dominant forms, and include upwards of 10,000 known species; while the various tribes into which the sub-family is divided include, as a rule, each many {207}genera; the Carabides are next in importance, with upwards of 2000 species, but are divided into a comparatively large number of tribes, each of which averages a much smaller number of genera than do the tribes of Harpalides; Pseudomorphides includes only about 100 species; and Mormolycides consists of the single genus _Mormolyce_ with three species.
FAM. 6. AMPHIZOIDAE.—_Antennae destitute of pubescence: outer lobe of maxilla not jointed; metasternum with a short transverse impressed line on the middle behind. Hind legs slender, not formed for swimming._ This family is limited to the genus _Amphizoa_; the species of which may be briefly described as lowly organised Carabidae that lead an aquatic life. The geographical distribution is highly remarkable, there being but three species, two of which live in Western North America, the third in Eastern Tibet. The habits of American _Amphizoa_ are known; they pass a life of little activity in very cold, rapid streams; they do not swim, but cling to stones and timber. The larva was recently discovered in Utah by Messrs. Hubbard and Schwarz:[90] it has the same habits as the perfect Insect, and in general form resembles the larvae of the genus _Carabus_; but it has no terminal tube to the body, the abdomen consisting of eight segments and a pair of short terminal appendages; the spiracles are obsolete, with the exception of a pair placed near to one another at the termination of the eighth abdominal segment. As regards the mouth this larva is Carabid, as regards the abdomen and stigmata Dytiscid of a primitive type.
[Illustration: Fig. 93—_Amphizoa lecontei._ North America. A, Larva; B, imago.]
{208}[Illustration: Fig. 94—_Pelobius tardus._ Britain. A, Young larva; B, adult larva; C, imago. (A and B after Schiödte.)]
FAM. 7. PELOBIIDAE.—_Antennae destitute of pubescence: outer lobe of maxilla jointed, metasternum with a short transverse impressed line on the middle behind. Hind legs rather slender, formed for swimming, the tarsi longer than the tibiae._ This family is limited to the one genus _Pelobius_ (_Hygrobia_ of some authors). Like _Amphizoa_, to which it is in several respects analogous, it has a singular geographical distribution; there are only four known species, one lives in Britain and the Mediterranean region, one in Chinese Tibet, two in Australia. _Pelobius_ may be briefly described as a Carabid adapted to a considerable extent for living in and swimming about in water; differing thus from _Amphizoa_, which has no special adaptation for swimming. The larva of _Pelobius_ is remarkable; it breathes by means of branchial filaments on the under surface of the body, the spiracles being present, though those of the abdomen are very minute and the others small. The head is very large, the mandibles are not tube-like, the food being taken after the manner of the Carabidae; the 8th abdominal segment ends in three long processes; the small 9th segment is retracted beneath them. The adult _Pelobius tardus_ is remarkable for its loud stridulation. The sound is produced by an apparatus described correctly by Charles Darwin;[91] {209}there is a file on the inside of the wing-cases, and the Insect turns up the tip of the abdomen and scrapes the file therewith. The Insects are called squeakers in the Covent Garden market, where they are sold.
[Illustration: Fig. 95—_Cnemidotus caesus._ England. A, Imago; B, larva, highly magnified. (After Schiödte.)]
FAM. 8. HALIPLIDAE.—_Antennae bare, ten-jointed; metasternum marked by a transverse line; posterior coxae prolonged as plates, covering a large part of the lower surface of the abdomen; the slender, but clubbed, hind femora move between these plates and the abdomen._ The Haliplidae are aquatic, and are all small, not exceeding four or five millimetres in length. The ventral plates are peculiar to the Insects of this family, but their function is not known. The larvae are remarkable on account of the fleshy processes disposed on their bodies; but they exhibit considerable variety in this respect; their mandibles are grooved so that they suck their prey. In the larva of _Haliplus_, according to Schiödte, there are eight pairs of abdominal spiracles, but in _Cnemidotus_ (Fig. 95, B), there are no spiracles, and air is obtained by means of a trachea traversing each of the long filaments. The Insects of these two genera are so similar in the imaginal instar that it is well worthy of note that their larvae should be distinguished by such important characters. Haliplidae is a small family consisting of three genera, having about 100 species; {210}it is very widely distributed. We have 13 species in Britain, all the genera being represented.
[Illustration: Fig. 96.—_Cybister roeseli_ (= _laterimarginalis_ De G.) Europe. A, Larva (after Schiödte); B, ♂ imago.]
FAM. 9. DYTISCIDAE (_Water-beetles_).—_Antennae bare; hind legs formed for swimming, not capable of ordinary walking: metasternum without a transverse line across it; behind closely united with the extremely large coxae. Outer lobe of maxilla forming a two-jointed palpus._ The Dytiscidae, or true water-beetles, are of interest because—unlike the aquatic Neuroptera—they exist in water in both the larval and imaginal instars; nevertheless there is reason for supposing that they are modified terrestrial Insects: these reasons are (1) that in their general organisation they are similar to the Carabidae, and they drown more quickly than the majority of land beetles do; (2) though the larvae are very different from the larvae of terrestrial beetles, yet the imaginal instars are much less profoundly changed, and are capable of existing perfectly well on land, and of taking prolonged flights through the air; (3) the pupa is, so far as known, always terrestrial. The larvae and imagos are perfectly at home in the water, except that they must come to the surface to get air. Some of them are capable, however, when quiescent, of living for hours together beneath the water, but there appears to be great diversity in this respect.[92] The hind pair of legs is the chief means of locomotion. These swimming-legs (Fig. 97) are deserving of admiration on account of their mechanical perfection; this, however, is exhibited in various {211}degrees, the legs in the genera _Dytiscus_ and _Hydroporus_ being but slender, while those of _Cybister_ are so broad and powerful, that a single stroke propels the Insect for a considerable distance.
[Illustration: Fig. 97—Hind- or swimming-leg of _Cybister tripunctatus_. A, The whole leg detached; B, the movable parts in the striking position. _a_, Coxa; _b_, trochanter; _c_, femur; _d_, tibia; _e_, last joint of tarsus.]
The wing-cases fit perfectly to the body, except at the tip, so as to form an air-tight space between themselves and the back of the Insect; this space is utilised as a reservoir for air. When the _Dytiscus_ feels the necessity for air it rises to the surface and exposes the tip of the body exactly at the level of the water, separating at the same time the abdomen from the wing-cases so as to open a broad chink at the spot where the parts were, during the Insect's submersion, so well held together as to be air- and water-tight. The terminal two pairs of spiracles are much enlarged, and by curving the abdomen the beetle brings them into contact with the atmosphere; respiration is effected by this means as well as by the store of air carried about under the wing cases. The air that enters the space between the elytra and body is shut in there when the Insect closes the chink and again dives beneath the water. The enlargement of the terminal stigmata in _Dytiscus_ is exceptional, and in forms more highly organised in other respects, such as _Cybister_, these spiracles remain minute; the presumption being that in this case respiration is carried on almost entirely by means of the supply the Insect carries in the space between the elytra and the base of the abdomen.[93] The structure of the front foot of the male _Dytiscus_, and of many other water-beetles, is highly remarkable, the foot being dilated to form a palette or saucer, covered beneath by sucker-like structures of great delicacy and beauty; by the aid of these the male is enabled to retain a position on the female for many hours, or even days, together. Lowne has shown that the {212}suckers communicate with a sac in the interior of the foot containing fluid, which exudes under pressure. As the portions of the skeleton of the female on which these suckers are brought to bear is frequently covered with pores, or minute pits, it is probable that some correlation between the two organisms is brought about by these structures. The females in many groups of Dytiscidae bear on the upper surface of the body a peculiar sculpture of various kinds, the exact use of which is unknown; in many species there are two forms of the female, one possessing this peculiar sculpture, the other nearly, or quite, without it. The larvae of Dytiscidae differ from those of Carabidae chiefly by the structure of the mouth and of the abdomen. They are excessively rapacious, and are indeed almost constantly engaged in sucking the juices of soft and small aquatic animals, by no means excluding their own kind. The mode of suction is not thoroughly known, but so far as the details have been ascertained they are correctly described, in the work on aquatic Insects, by Professor Miall, we have previously referred to; the mandibles are hollow, with a hole near the tip and another at the base, and being sharp at the tips are thrust into the body of a victim, and then by their closure the other parts of the mouth, which are very beautifully constructed for the purpose, are brought into fitting mechanical positions for completing the work of emptying the victim. Nagel states that the larva of _Dytiscus_ injects a digestive fluid into the body of its victim, and that this fluid rapidly dissolves all the more solid parts of the prey, so that the rapacious larva can easily absorb all its victim except the insoluble outer skin. The abdomen consists of only eight segments, and a pair of terminal processes; the stigmata are all more or less completely obsolete—according to species—with the exception of the pair on the eighth segment at the tip of the body; the terminal segments are frequently fringed with hairs, that serve not only as means of locomotion, but also to float the pair of active stigmata at the surface when the creature rises to get air. Although the larvae of Dytiscidae are but little known, yet considerable diversity has already been found. Those of _Hyphydrus_ and some species of _Hydroporus_ have the front of the head produced into a horn, which is touched by the tips of the mandibles.
Dytiscidae are peculiar inasmuch as they appear to flourish {213}best in the cooler waters of the earth. Lapland is one of the parts of Europe richest in Dytiscidae, and the profusion of species in the tropics compared with those of Europe is not nearly so great as it is in the case of most of the other families of Coleoptera. About 1800 species are at present known, and we have rather more than 100 species in Britain.[94]
SERIES III. POLYMORPHA.
_Antennae frequently either thicker at the tip (clavicorn) or serrate along their inner edge (serricorn); but these characters, as well as the number of joints in the feet and other points, are very variable._
Upwards of fifty families are placed in this series; many of these families are of very small extent, consisting of only a few species; other families of the series are much larger, so that altogether about 40,000 species—speaking broadly, about one-fourth of the Coleoptera—are included in the series. We have already (p. 189) alluded to the fact that it is formed by certain conventional series, Clavicornia, Serricornia, etc. united, because it has hitherto proved impossible to define them.
FAM. 10. PAUSSIDAE.—_Antennae of extraordinary form, usually two-jointed, sometimes six- or ten-jointed. Elytra elongate, but truncate behind, leaving the pygidium exposed. Tarsi five-jointed._ The Paussidae have always been recognised as amongst the most remarkable of beetles, although they are of small size, the largest attaining scarcely half an inch in length. They are found only in two ways; either in ants' nests, or on the wing at night. They apparently live exclusively in ants' nests, but migrate much. Paussidae usually live in the nests of terrestrial ants, but they have been found in nests of _Cremastogaster_ in the spines of _Acacia fistulosa_. They have the power of discharging, in an explosive manner, a volatile caustic fluid from the anus, which is said by Loman to contain free iodine. Their relations to the ants are at present unexplained, though much attention has been given to the subject. When observed in the nests they frequently appear as if asleep, and the ants do not take much notice of them.
{214}[Illustration: Fig. 98.—_Paussus cephalotes_ ♂. El Hedjaz. (After Raffray.)]
On other occasions the ants endeavour to drag them into the interior of the nest, as if desirous of retaining their company: the _Paussus_ then makes no resistance to its hosts; if, however, it be touched, even very slightly, by an observer, it immediately bombards: the ants, as may be imagined, do not approve of this, and run away. Nothing has ever been observed that would lead to the belief that the ants derive any benefit from the presence of the Paussi, except that these guests bear on some part of the body—frequently the great impressions on the pronotum—patches of the peculiar kind of pubescence that exists in many other kinds of ants'-nest beetles, and is known in some of them to secrete a substance the ants are fond of, and that the ants have been seen to lick the beetles. On the other hand, the Paussi have been observed to eat the eggs and larvae of the ants. The larva of _Paussus_ is not known,[95] and Raffray doubts whether it lives in the ants' nests. There are about 200 species of Paussidae known, Africa, Asia and Australia being their chief countries; one species, _P. favieri_, is not uncommon in the Iberian peninsula and South France, and a single species was formerly found in Brazil. The position the family should occupy has been much discussed; the only forms to which they make any real approximation are Carabidae, of the group Ozaenides, a group of ground beetles that also crepitate. Burmeister and others have therefore placed the Paussidae in the series Adephaga, but we follow Raffray's view (he being the most recent authority on the family),[96] who concludes that this is an anomalous group not intimately connected with any other family of Coleoptera, though having more affinity to Carabidae than to anything else. The recently discovered genus _Protopaussus_ has eleven joints to the antennae, and is said to come nearer to Carabidae than the previously known forms did, and we may anticipate that a more extensive knowledge will show that the family may find a natural place in the Adephaga. The description of the abdomen given by Raffray is erroneous; in a specimen of the genus _Arthropterus_ the writer has dissected, he finds that there {215}are five ventral segments visible along the middle, six at the sides, as in the families of Adephaga generally. There is said to be a great difference in the nervous systems of Carabidae and Paussidae, but so little is known on this point that we cannot judge whether it is really of importance.
[Illustration: Fig. 99.—A, Larva of _Gyrinus_ (after Schiödte); B, under side of _Gyrinus_ sp. (after Ganglbauer). 1, Prosternum; 2, anterior coxal cavity; 3. mesothoracic episternum; 4, mesoepimeron; 5, mesosternum; 6, metathoracic episternum; 7, middle coxal cavity; 8, metasternum; 9, hind coxa; 10, ventral segments. [N.B.—The first ventral segment really consists, at each side, of two segments united; this may be distinctly seen in many Gyrinidae.]]
FAM. 11. GYRINIDAE (_Whirligig beetles_).—_Antennae very short; four eyes; middle and hind legs forming short broad paddles; abdomen with six segments visible along the middle, seven along each side._ These Insects are known to all from their habit of floating lightly on the surface of water, and performing graceful complex curves round one another without colliding; sometimes they may be met with in great congregations. They are admirably constructed for this mode of life, which is comparatively rare in the Insect world; the Hydrometridae amongst the bugs, and a small number of different kinds of Diptera, being the only other Insects that are devoted to a life on the surface of the waters. Of all these, Gyrinidae are in their construction the most adapted for such a career. They are able to dive to escape danger, and they then carry with them a small supply of air, but do not stay long beneath the surface. Their two hind pairs of legs are beautifully constructed as paddles, expanding mechanically when moved in the backward direction, and collapsing into an extremely small space directly the resistance they meet with is in the other direction. The front legs of these Insects are articulated to the thorax in a peculiar direction so that their soles do not look {216}downwards but towards one another; hence the sensitive adhesive surface used during coupling is placed on the side of the foot, forming thus a false sole: a remarkable modification otherwise unknown in Insects. They breathe chiefly by means of the very large metathoracic spiracles.
The larvae (Fig. 99, A) are purely aquatic, and are highly modified for this life, being elongate creatures, with sharp, mandibles and nine abdominal segments, each segment bearing on each side a trachea branchia; these gills assist to some extent in locomotion. The stigmata are quite obsolete, but the terminal segment bears four processes, one pair of which may be looked on as cerci, the other as a pair of gills corresponding with the pair on each of the preceding segments. The mandibles are not suctorial, but, according to Meinert, possess an orifice for the discharge of the secretion of a mandibular gland. Gyrinidae are chiefly carnivorous in both the larval and imaginal instars. Fully 300 species are known; they are generally distributed, though wanting in most of the islands of the world except those of large size. The finest forms are the Brazilian _Enhydrus_ and the _Porrorhynchus_ of tropical Asia.[97] In Britain we have nine species, eight of _Gyrinus_, one of _Orectochilus_; the latter form is rarely seen, as it hides during the day, and performs its rapid gyrations at night.
The Gyrinidae are one of the most distinct of all the families of Coleoptera: by some they are associated in the Adephagous series; but they have little or no affinity with the other members thereof. Without them the Adephaga form a natural series of evidently allied families, and we consider it a mistake to force the Gyrinidae therein because an objection is felt by many taxonomists to the maintenance of isolated families. Surely if there are in nature some families allied and others isolated, it is better for us to recognise the fact, though it makes our classifications look less neat and precise, and increases the difficulty of constructing "tables."
FAM. 12. HYDROPHILIDAE.—_Tarsi five-jointed, the first joint in many cases so small as to be scarcely evident: antennae short, of less than eleven joints, not filiform, but consisting of {217}three parts, a basal part of one or two elongate joints, an intermediate part of two or more small joints, and an apical part of larger (or at any rate broader) joints, which are pubescent, the others being bare. Outer lobe of maxillae usually complex, but not at all palpiform, maxillary palpi often very long; the parts of the labium much concealed behind the mentum, the labial palpi very widely separated. Hind coxae extending the width of the body, short, the lamina interior small in comparison with the lamina exterior. Abdomen of five visible segments._ The Hydrophilidae are an extensive family of beetles, unattractive in colours and appearance, and much neglected by collectors. A large part of the family live in water, though most of them have only feeble powers of aquatic locomotion, and the beetles appear chiefly to devote their attention to economising the stock of air each individual carries about. The best known forms of the family are the species of _Hydrophilus_. They are, however, very exceptional in many respects, and are far more active and predaceous than most of the other forms. Much has been written about _Hydrophilus piceus_, one of the largest of British beetles. This Insect breathes in a most peculiar manner: the spiracles are placed near bands of delicate pubescence, forming tracts that extend the whole length of the body, and in this particular species cover most of the under surface of the body; these velvety tracts retain a coating of air even when the Insect is submerged and moves quickly through the water. It would appear rather difficult to invent a mechanism to supply these tracts with fresh air without the Insect leaving the water; but nevertheless such a mechanism is provided by the antennae of the beetle, the terminal joints of which form a pubescent scoop, made by some longer hairs into a funnel sufficiently large to convey a bubble of air. The Insect therefore rises to the surface, and by means of the antennae, which it exposes to the air, obtains a supply with which it surrounds a large part of its body; for, according to Miall, it carries a supply on its back, under the elytra, as well as on its ventral surface. From the writer's own observations, made many years ago, he inclines to the opinion that the way in which the _Hydrophilus_ uses the antennae to obtain air varies somewhat according to circumstances.
Many of the members of the sub-family Hydrophilides construct egg-cocoons. In the case of _Hydrophilus piceus_, the {218}boat-like structure is provided with a little mast, which is supposed by some to be for the purpose of securing air for the eggs. _Helochares_ and _Spercheus_ (Fig. 100) carry the cocoon of eggs attached to their own bodies. _Philydrus_ constructs, one after the other, a number of these egg-bags, each containing about fifteen eggs, and fixes each bag to the leaf of some aquatic plant; the larvae as a rule hatch speedily, so that the advantage of the bag is somewhat problematic.
[Illustration: Fig. 100.—_Spercheus emarginatus_ ♀. Britain. A, Upper surface of beetle; B, under surface of abdomen, with the egg-sac ruptured and some of the eggs escaping.]
The larvae of the aquatic division of the family have been to a certain extent studied by Schiödte and others; those of the Sphaeridiides—the terrestrial group of the family—are but little known. All the larvae seem to be predaceous and carnivorous, even when the imago is of vegetable-feeding habits; and Duméril states that in _Hydrous caraboides_ the alimentary canal undergoes a great change at the period of metamorphosis, becoming very elongate in the adult, though in the larva it was short. The legs are never so well developed as they are in the Adephaga, the tarsi being merely claw-like or altogether wanting; the mandibles are never suctorial. The respiratory arrangements show much diversity. In most of the Hydrophilides the process is carried on by a pair of terminal spiracles on the eighth abdominal segment, as in Dytiscidae, and these are either exposed or placed in a respiratory chamber. In _Berosus_ the terminal stigmata are obsolete, and the sides of the body bear long branchial filaments. Cussac says that in _Spercheus_ (Fig. 101) there are seven pairs of abdominal spiracles, and that the larva breathes by presenting these to the air;[98] but Schiödte states that in this form there are neither thoracic nor abdominal spiracles, except a pair placed in a respiratory chamber on the eighth segment of the abdomen, after the manner described by Miall as existing in _Hydrobius_. No doubt Cussac was wrong in supposing the peculiar lateral abdominal processes to be {219}stigmatiferous. In _Berosus_ there are patches of aëriferous, minute pubescence on the body. The pupae of Hydrophilides repose on the dorsal surface, which is protected by spinous processes on the pronotum, and on the sides of the abdomen.
We have already remarked that this is one of the most neglected of the families of Coleoptera, and its classification is not satisfactory. It is usually divided into Hydrophilides and Sphaeridiides. The Sphaeridiides are in large part terrestrial, but their separation from the purely aquatic Hydrophilides cannot be maintained on any grounds yet pointed out. Altogether about 1000 species of Hydrophilidae are known, but this probably is not a tenth part of those existing. In Britain we have nearly ninety species. Some taxonomists treat the family as a series with the name Palpicornia. The series Philhydrida of older authors included these Insects and the Parnidae and Heteroceridae.
[Illustration: Fig. 101—Larva of _Spercheus emarginatus_. (After Schiödte).]
FAM. 13. PLATYPSYLLIDAE.—This consists of a single species. It will be readily recognised from Fig. 102, attention being given to the peculiar antennae, and to the fact that the mentum is trilobed behind. This curious species has been found only on the beaver. It was first found by Ritsema on American beavers (_Castor canadensis_) in the Zoological Gardens at Amsterdam, but it has since been found on wild beavers in the Rhone in France; in America it appears to be commonly distributed on these animals from Alaska to Texas. It is very remarkable that a wingless parasite of this kind should be found in both hemispheres. The Insect was considered by Westwood to be a separate Order called Achreioptera, but there can be no doubt that it is a beetle. It is also admitted that it shows some points of resemblance with Mallophaga, the habits of which are similar. Its Coleopterous nature is confirmed by the larva, which has been described by both Horn and Riley.[99] Little is known as to the food and life-history. Horn states that the eggs are placed on {220}the skin of the beaver amongst the densest hair; the larvae move with a sinuous motion, like those of Staphylinidae. It has been suggested that the Insect feeds on an Acarid, _Schizocarpus mingaudi_; others have supposed that it eats scales of epithelium or hairs of the beaver.
[Illustration: Fig. 102—_Platypsyllus castoris._ A, Upper side; B, lower side, with legs of one side removed; C, antenna. (After Westwood.)]
[Illustration: Fig. 103—_Leptinus testaceus._ Britain.]
FAM. 14. LEPTINIDAE.—_Antennae rather long, eleven-jointed, without club, but a little thicker at the extremity. Eyes absent or imperfect. Tarsi five-jointed. Elytra quite covering abdomen. Mentum with the posterior angles spinously prolonged._ A family of only two genera and two species. Their natural history is obscure, but is apparently of an anomalous nature; the inference that may be drawn from the little that is known being that they are parasitic on mammals. There is little or nothing in their structure to indicate this, except the condition of blindness; and until recently the Insects were classified amongst Silphidae. _Leptinus testaceus_ (Fig. 103) is a British Insect, and besides occurring in Europe is well known in North America. In Europe it has been found {221}in curious places, including the nests of mice and bumble-bees. In America it has been found on the mice themselves by Dr. Ryder, and by Riley in the nests of a common field-mouse, together with its larva, which, however, has not been described. The allied genus _Leptinillus_ is said by Riley to live on the beaver, in company with _Platypsyllus_.[100] It has been suggested that the natural home of the _Leptinus_ is the bee's nest, and that perhaps the beetle merely makes use of the mouse as a means of getting from one nest of a bumble-bee to another.
FAM. 15. SILPHIDAE.—_The mentum is usually a transverse plate, having in front a membranous hypoglottis, which bears the exposed labial palpi, and immediately behind them the so-called bilobed ligula. The anterior coxae are conical and contiguous: prothoracic epimera and episterna not distinct. Visible abdominal segments usually five, but sometimes only four, or as many as seven. Tarsi frequently five-jointed, but often with one joint less. Elytra usually covering the body and free at the tips, but occasionally shorter than the body, and even truncate behind so as to expose from one to four of the dorsal plates; but there are at least three dorsal plates in a membranous condition at the base of the abdomen._ These beetles are extremely diverse in size and form, some being very minute, others upwards of an inch long, and there is also considerable range of structure. In this family are included the burying-beetles (_Necrophorus_), so well known from their habit of making excavations under the corpses of small Vertebrates, so as to bury them. Besides these and _Silpha_, the roving carrion-beetles, the family includes many other very different forms, amongst them being the larger part of the cave-beetles of Europe and North America. These belong mostly to the genera _Bathyscia_ in Europe, and _Adelops_ in North America; but of late years quite a crowd of these eyeless cave-beetles of the group Leptoderini have been discovered, so that the European catalogue now includes about 20 genera and 150 species. The species of the genus _Catopomorphus_ are found in the nests of ants of the genus _Aphaenogaster_ in the Mediterranean region. Scarcely anything is known as to the lives of either the cave-Silphidae or the myrmecophilous forms.
The larvae of several of the larger forms of Silphidae are well known, but very little has been ascertained as to the smaller forms. {222}Those of the burying-beetles have spiny plates on the back of the body, and do not resemble the other known forms of the family. The rule is that the three thoracic segments are well developed, and that ten abdominal segments are also distinct; the ninth abdominal segment bears a pair of cerci, which are sometimes elongate. Often the dorsal plates are harder and better developed than is usual in Coleopterous larvae. This is especially the case with some that are endowed with great powers of locomotion, such as _S. obscura_ (Fig. 104). The food of the larvae is as a rule decomposing animal or vegetable matter, but some are predaceous, and attack living objects. The larger _Silpha_ larvae live, like the _Necrophorus_, on decomposing animal matter, but run about to seek it; hence many specimens of some of these large larvae may sometimes be found amongst the bones of a very small dead bird. We have found the larva and imago of _S. thoracica_ in birds' nests containing dead nestlings. _S. atrata_ and _S. laevigata_ make war on snails. _S. lapponica_ enters the houses in Lapland and ravages the stores of animal provisions. _S. opaca_ departs in a very decided manner from the habits of its congeners, as it attacks beetroot and other similar crops in the growing state; it is sometimes the cause of serious loss to the growers of beet. The larvae of the group Anisotomides are believed to be chiefly subterranean in habits; that of _A. cinnamomea_ feeds on the truffle, and the beetle is known as the truffle-beetle.
[Illustration: Fig. 104—A, Larva of _Silpha obscura_. Europe. (After Schiödte). B, _Ptomaphila lacrymosa_, Australia.]
The number of species of Silphidae known must be at present nearer 900 than 800. Of these an unusually large proportion belong to the European and North American regions; Silphidae being apparently far from numerous in the tropics. Rather more than 100 species are natives of Britain. The family reappears in considerable force in New Zealand, and is probably well represented {223}in South Australia and Tasmania. The most remarkable form known is perhaps the Australian genus _Ptomaphila_ (Fig. 104, B). The classification of the family is due to Dr. Horn.[101] The only change of importance that has since been suggested is the removal of _Sphaerites_ from this family to Synteliidae. Anisotomidae and Clambidae have been considered distinct families, but are now included in Silphidae.
FAM. 16. SCYDMAENIDAE.—_Minute Insects allied to Silphidae, but with the hind coxae separated, and the facets of the eyes coarser; the tarsi are five-jointed; the number of visible abdominal segments is six._ These small beetles are widely spread over the earth's surface, and about 700 species are now known, of which we have about a score in Britain; many live in ants' nests, but probably usually rather as intruders than as guests that have friendly relations with their hosts. Nothing is known as to their life-histories, but the food of the imago, so far as is known, consists of Acari. _Mastigus_ is a very aberrant form, found in moss and dead leaves in Southern Europe. By means of _Brathinus_ the family is brought very near to Silphidae; Casey, however, considers _Brathinus_ to belong to Staphylinidae rather than to Scydmaenidae. The South European _Leptomastax_ is remarkable on account of the slender, long, sickle-shaped mandibles. The Oriental genus _Clidicus_ is the largest and most remarkable form of the family; it has a very slender neck to its broad head, and is more than a quarter of an inch long.
FAM. 17. GNOSTIDAE.—_Minute Insects with three-jointed antennae, five-jointed tarsi, and three apparent ventral segments, the first of which, however, is elongate, and consists of three united plates. Elytra entirely covering the after-body._ The family consists of two species which have been found in the nests of ants, of the genus _Cremastogaster_, in Brazil.[102]
FAM. 18. PSELAPHIDAE.—_Very small Insects; the elytra much abbreviated, usually leaving as much as half the abdomen uncovered; the maxillary palpi usually greatly developed, and of a variety of remarkable forms; the segments of the abdomen not more than seven in number, with little or no power of movement. Tarsi with not more than three joints._ These small Coleoptera mostly live in the nests of ants, and present a great diversity of extraordinary {224}shapes, and very peculiar structures of the antennae and maxillary palpi. Owing to the consolidation of some of its segments, the abdomen frequently appears to have less than the usual number. In the curious sub-family Clavigerides, the antennae may have the joints reduced to two or even, to all appearance, to one; the tarsi suffer a similar reduction. There are about 2500 species of Pselaphidae known; many of them have never been found outside the ants' nests; very little, however, is known as to their natural history. It is certain that some of them excrete, from little tufts of peculiar pubescence, a substance that the ants are fond of. The secretory patches are found on very different parts of the body and appendages. _Claviger testaceus_ is fed by the ants in the same way as these social Insects feed one another; the _Claviger_ has also been seen to eat the larvae of the ants. They ride about on the backs of the ants when so inclined. The family is allied to Staphylinidae, but is easily distinguished by the rigid abdomen. Only one larva—that of _Chennium bituberculatum_—is known. It appears to be very similar to the larvae of Staphylinidae. The best account of classification and structure is that given by M. Achille Raffray,[103] who has himself discovered and described a large part of the known species.
FAM. 19. STAPHYLINIDAE.—_Elytra very short, leaving always some of the abdominal segments exposed, and covering usually only two of the segments. Abdomen usually elongate, with ten dorsal, and seven or eight ventral segments; of the latter six or seven are usually exposed; the dorsal plates as hard as the ventral, except sometimes in the case of the first two segments; the segments very mobile, so that the abdomen can be curled upwards. The number of tarsal joints very variable, often five, but frequently as few as three, and not always the same on all the feet._ Staphylinidae (formerly called Brachelytra or Microptera) is one of the most extensive of even the great families of Coleoptera; notwithstanding their diversity, they may in nearly all cases be recognised by the more than usually mobile and uncovered abdomen, combined with the fact that the parts of the mouth are of the kind we have mentioned in Silphidae. The present state of the classification of this family has been recently discussed by Ganglbauer.[104]
{225}[Illustration: Fig. 105—Staphylinidae. A, Larva of _Philonthus nitidus_. Britain. (After Schiödte.) B, _Ocypus olens_, Britain; C, tip of abdomen, of _O. olens_ with stink-vessels.]
At present about 9000 species are known, some of which are minute, while scarcely any attain a size of more than an inch in length, our common British black cock-tail, or "devil's coach-horse beetle," _Ocypus olens_, being amongst the largest. Though the elytra are short, the wings in many forms are as large as those of the majority of beetles; indeed many Staphylinidae are more apt at taking flight than is usual with Coleoptera; the wings when not in use are packed away under the short elytra, being transversely folded, and otherwise crumpled, in a complicated but orderly manner. It is thought that the power of curling up the abdomen is connected with the packing away of the wings after flight; but this is not the case: for though the Insect sometimes experiences a difficulty in folding the wings under the elytra after they have been expanded, yet it overcomes this difficulty by slight movements of the base of the abdomen, rather than by touching the wings with the tip. What the value of this exceptional condition of short elytra and corneous dorsal abdominal segments to the Insect may be is at present quite mysterious. The habits of the members of the family are very varied; many run with great activity; the food is very often small Insects, living or dead; a great many are found in fungi of various kinds, and perhaps eat them. It is in this family that we meet with some of the most remarkable cases of symbiosis, i.e. lives of two kinds of creatures mutually accommodated with good will. The relations between the Staphylinidae of the genera _Atemeles_ and _Lomechusa_, and certain ants, in the habitations of which they dwell, are very interesting. The beetles are never found out of the ants' nests, or at any rate not very far from them. The most friendly relations exist between them and the ants: they have patches of yellow hairs, and these {226}apparently secrete some substance with a flavour agreeable to the ants, which lick the beetles from time to time. On the other hand, the ants feed the beetles; this they do by regurgitating food, at the request of the beetle, on to their lower lip, from which it is then taken by the beetle (Fig. 82). The beetles in many of their movements exactly resemble the ants, and their mode of requesting food, by stroking the ants in certain ways, is quite ant-like. So reciprocal is the friendship that if an ant is in want of food, the _Lomechusa_ will in its turn disgorge for the benefit of its host. The young of the beetles are reared in the nests by the ants, who attend to them as carefully as they do to their own young. The beetles have a great fondness for the ants, and prefer to sit amongst a crowd thereof; they are fond of the ants' larvae as food, and indeed eat them to a very large extent, even when their own young are receiving food from the ants. The larva of _Lomechusa_, as described by Wasmann (to whom we are indebted for most of our knowledge of this subject),[105] when not fully grown, is very similar to the larvae of the ants; although it possesses legs it scarcely uses them: its development takes place with extraordinary rapidity, two days, at most, being occupied in the egg, and the larva completing its growth in fourteen days. Wasmann seems to be of opinion that the ants scarcely distinguish between the beetle-larvae and their own young; one unfortunate result for the beetle follows from this, viz. that in the pupal state the treatment that is suitable for the ant-larvae does not agree with the beetle-larvae: the ants are in the habit of digging up their own kind and lifting them out and cleaning them during their metamorphosis; they also do this with the beetle-larvae, with fatal results; so that only those that have the good fortune to be forgotten by the ants complete their development. Thus from thirty _Lomechusa_ larvae Wasmann obtained a single imago, and from fifty _Atemeles_ larvae not even one.
Many other Staphylinidae are exclusively attached to ants' nests, but most of them are either robbers, at warfare with the ants—as is the case with many species of _Myrmedonia_ that lurk about the outskirts of the nests—or are merely tolerated by the ants, not receiving any direct support from them. The most {227}remarkable Staphylinidae yet discovered are some viviparous species, forming the genera _Corotoca_ and _Spirachtha_, that have very swollen abdomens, and live in the nests of Termites in Brazil:[106] very little is, however, known about them. A very large and powerful Staphylinid, _Velleius dilatatus_, lives only in the nests of hornets and wasps. It has been supposed to be a defender of the Hymenoptera, but the recent observations of Janet and Wasmann make it clear that this is not the case: the _Velleius_ has the power of making itself disagreeable to the hornets by some odour, and they do not seriously attack it. The _Velleius_ finds its nutriment in larvae or pupae of the wasps that have fallen from their cells, or in other organic refuse.
The larvae of Staphylinidae are very similar to those of Carabidae, but their legs are less perfect, and are terminated only by a single claw; there is no distinct labrum. The pupae of some are obtected, _i.e._ covered by a secondary exudation that glues all the appendages together, and forms a hard coat, as in Lepidoptera. We have about 800 species of Staphylinidae in Britain, and it is probable that the family will prove one of the most extensive of the Order. It is probable that one hundred thousand species or even more are at present in existence.
FAM. 20. SPHAERIIDAE.—_Very minute. Antennae eleven-jointed, clubbed. Tarsi three-jointed. Abdomen with only three visible ventral segments_. This family includes only three or four species of Insects about 1/50 of an inch long. They are very convex, and be found walking on mud. _S. acaroides_ occurs in our fens. Mr. Matthews considers that they are most nearly allied to Hydrophilidae.[107]
[Illustration: Fig. 106—_Trichopteryx fascicularis_. Britain. A, Outline of perfect Insect; B, part of upper surface; C, larva from side; D, from above; E, pupa; F, wing; G, natural size of imago.]
FAM. 21. TRICHOPTERYGIDAE.—_Extremely minute: antennae {228}clavicorn (basal and apical joints thicker than middle joints); tarsi three-jointed; elytra sometimes covering abdomen, in other cases leaving a variable number of segments exposed; wings fringed._ This family comprises the smallest Insects; _Nanosella fungi_ being only 1/100 of an inch long, while the largest Trichopterygid is only 1/12 of an inch. The small size is not accompanied by any degeneration of structure, the minute, almost invisible forms, having as much anatomical complexity as the largest Insects. Very little is known as to the natural history. Probably these Insects exist in all parts of the world, for we have about eighty species in England, and Trichopterygidae are apparently numerous in the tropics.[108]
FAM. 22. HYDROSCAPHIDAE.—_Extremely minute aquatic Insects, with elongate abdomen. Antennae eight-jointed._ The other characters are much the same as those we have mentioned for Trichopterygidae. The family is not likely to come before the student, as only three or four species from Southern Europe and North America are known.[109]
[Illustration: Fig. 107—A, Larva of _Orthoperus brunnipes_ (after Perris); B, _O. atomarius_, perfect Insect. Britain.]
FAM. 23. CORYLOPHIDAE.—_Minute beetles. Tarsi four-jointed, but appearing only three-jointed, owing to the hind joint being concealed by the emarginate (or notched) second joint. Six free ventral segments. Maxillae with only one lobe. Antennae of peculiar form._ There are about 200 species of these little Insects, but the family is apparently represented all over the world, and will probably prove to be much more extensive. The peculiar larva of _Orthoperus brunnipes_ was found abundantly by Perris in thatch in France. Mr. Matthews proposes to separate the genus _Aphanocephalus_ as a distinct family, Pseudocorylophidae.[110] In Corylophidae the wings are fringed with long hairs, as is the case in so many small Insects: the species of _Aphanocephalus_ are rather larger Insects, and the wings are not fringed; the tarsi are only three-jointed.
{229}FAM. 24. SCAPHIDIIDAE.—_Front coxae small, conical; prothorax very closely applied to the after-body; hind coxae transverse, widely separated: abdomen with six or seven visible ventral plates; antennae at the extremity with about five joints that become gradually broader. Tarsi five-jointed._ This family consists of a few beetles that live in fungi, and run with extreme rapidity; they are all small, and usually rare in collections. Some of the exotic forms are remarkable for the extreme tenuity and fragility of the long antennae, which bear fine hairs. The number of described species does not at present reach 200, but the family is very widely distributed. We have three or four species in Britain. All we know of the larvae is a description of that of _Scaphisoma agaricinum_ by Perris;[111] it is like the larva of Staphylinidae, there are nine abdominal segments in addition to a very short, broad pseudopod, and very short cerci. This larva feeds on agarics; it goes through its development in about three weeks; unlike the adult it is not very active.
[Illustration: Fig. 108—_Scaphisoma agaricinum._ Britain. A Larva (after Perris); B perfect Insect.]
FAM. 25. SYNTELIIDAE.—_Antennae clavicorn, with very large club: labium, with hypoglottis and the parts beyond it, exposed. Front coxae transverse. Abdomen with five visible ventral segments, and eight or nine dorsal, the basal four of which are semi-corneous._ This family includes only five species; its classification has given rise to much difference of opinion. We have, after consideration of all its characters, established it as a distinct family[112] allied to Silphidae. The perfect Insects live on the sap running from trees: but nothing else is known of their natural history. Like so many others of the very small families of aberrant Coleoptera, it has a very wide distribution; _Syntelia_ being found in Eastern Asia and Mexico, while the sub-family Sphaeritides occurs, as a single species, in Europe and North America. The earlier instars are unknown.
[Illustration: Fig. 109—_Syntelia westwoodi._ Mexico. (From _Biol. Centr. Amer._)]
{230}[Illustration: Fig. 110—_Platysoma depressum._ Europe. A, Larva (after Schiödte); B, perfect Insect.]
FAM. 26. HISTERIDAE.—_Very compact beetles, with very hard integument, short, bent antennae, with a very compact club: no hypoglottis. Elytra closely applied to body, but straight behind, leaving two segments exposed. Abdomen with five visible ventral segments; with seven dorsal segments, all hard. Front coxae strongly transverse, hind coxae widely separated._ The extremely compact form, and hard integument, combined with the peculiar antennae—consisting of a long basal joint, six or seven small joints, and then a very solid club of three joints covered with minute pubescence—render these Insects unmistakable. The colour is usually shining black, but there are numerous departures from this. The way in which these Insects are put together so as to leave no chink in their hard exterior armour when in repose, is very remarkable. The mouth-parts are rather highly developed, and the family is entitled to a high rank; it consists at present of about 2000 species;[113] in Britain we have about 40. The larvae are without ocelli or labrum, but have well-developed mandibles, the second and third thoracic segments being short, the ninth segment of the abdomen terminal, with two distinctly jointed cerci.[114] Histeridae are common in dung, in carcases, decaying fungi, etc., and some live under bark—these being, in the case of the genus _Hololepta_, very flat. Some are small cylinders, elaborately constructed, for entering the burrows of Insects in wood (_Trypanaeus_); a certain number are peculiar to ants' nests. Formerly it was supposed that the Insects were nourished on the decaying substances, but it is now believed, with good reason, that they are eminently predaceous, in both larval and imaginal {231}instars, and devour the larvae of Diptera, etc. The relations of the ants'-nest forms to the ants is not made out, but it is highly probable that they eat the ants' larvae, and furnish the ants with some dainty relish. A few species live in company with Termites.
FAM. 27. PHALACRIDAE.—_Body very compact; elytra entirely covering it; apical joints of antennae rather broader, usually long; front coxae globular; posterior coxae contiguous; abdomen with five visible ventral segments; tarsi five-jointed, fourth joint usually small and obscure._ This family consists entirely of small Insects: the tarsal structure is very aberrant, and is also diverse, so that the student may without careful observation pass the Insects over as having only four-jointed tarsi; their structure, so far as the front two pairs are concerned, being very nearly that of many Phytophaga. The larvae live in the heads of flowers, especially of the flowers of Compositae. Having bored their way down the stems, they pupate in earthen cocoons. Heeger[115] says that he has observed in favourable seasons six generations; but the larvae die readily in unfavourable seasons, and are destroyed in vast numbers when the meadows are mowed. Seven years ago very little was known as to the family, and the list of their species scarcely amounted to 100, but now probably 300 are described. They occur in all parts of the world; we have fourteen in Britain.
[Illustration: Fig. 111—_Olibrus bicolor._ Europe. A, Larva (after Heeger); B, perfect Insect.]
FAM. 28. NITIDULIDAE.—_Antennae with a three-jointed club; all the coxae separated, and each with an external prolongation; tarsi five-jointed, the fourth joint smaller than any of the others; abdomen with five visible plates._ These Insects are numerous, about 1600 species being at present known; in many of them the elytra nearly or quite cover the hind body, but in many others they are more or less abbreviated; in this case the Insects may be distinguished from Staphylinidae by the form of their antennae, and the smaller number of visible ventral segments. The habits are very varied, a great many are found on flowers, others are attracted by the sap of trees; some live in carcases. We have about 90 species in Britain; several forms of {232}the genera _Meligethes_ and _Epuraea_ are among the most abundant of our beetles. Most of what is known as to the larvae is due to Perris; several have been found living in flowers; that of _Pria_ haunts the flower of _Solanum dulcamara_ at the junction of the stamens with the corolla; the larva of _Meligethes aeneus_ sometimes occasions much loss by preventing the formation of seed in cultivated Cruciferae, such as Rape. These floricolous larvae grow with great rapidity, and then leave the flowers to pupate in the ground. The larva of _Nitidula_ lives in carcases, though it is not very different from that of _Pria_. The larva of _Soronia_ lives in fermenting sap, and has four hooks curving upwards at the extremity of the body. The curious genus _Cybocephalus_ consists of some very small, extremely convex Insects that live in flowers in Southern Europe; they have only four joints to the tarsi. The perfect Insects of the group Ipides are remarkable from having a stridulating organ on the front of the head. The classification of the well-known genus _Rhizophagus_ has given rise to much discussion; although now usually placed in Nitidulidae, we think it undoubtedly belongs to Cucujidae.
[Illustration: Fig. 112—_Pria dulcamarae._ Britain. A, Larva (after Perris); B, perfect Insect.]
[Illustration: Fig. 113—_Temnochila coerulea._ Europe. A, Larva (after Perris); B, perfect Insect.]
FAM. 29. TROGOSITIDAE.—_Differs from Nitidulidae in the structure of the tarsi; these appear to be four-jointed, with the third joint similar in size and form to the preceding; they are, however, really five-jointed, an extremely short basal joint being present. Hind coxae contiguous. The club of each antenna is bilaterally asymmetric, and the sensitive surface is confined to certain parts of the joints._ There are some 400 or 500 species of Trogositidae, but nearly all of them are exotic. The larvae (Fig. 113, A), are predaceous, destroying other larvae in large numbers, and it is probable that the imagos do the same. The larva of _Tenebroides_ (better known as _Trogosita_) _mauritanica_ is found in corn and flour, and is said to have sometimes been very {233}injurious by eating the embryo of the corn, but it is ascertained that it also devours certain other larvae that live on the corn. This beetle has been carried about by commerce, and is now nearly cosmopolitan. Our three British species of Trogositidae represent the three chief divisions of the family, viz. Nemosomides, Temnochilides, Peltides; they are very dissimilar in form, the Peltides being oval, with retracted head. It is doubtful whether the members of the latter group are carnivorous in any of their stages; it is more probable that they live on the fungi they frequent. Peltidae stand as a distinct family in many works.[116]
[Illustration: Fig. 114—_Bitoma crenata._ Britain. A, Larva (after Perris); B, perfect Insect.]
FAM. 30. COLYDIIDAE.—_Antennae with a terminal club, tarsi four-jointed, none of the joints broad; front and middle coxae small, globose, embedded; hind coxae transverse, either contiguous or separated; five visible ventral segments, several of which have no movement._ This is a family of interest, owing to the great diversity of form, to the extraordinary sculpture and clothing exhibited by many of its members, and to the fact that most of its members are attached to the primitive forests, and disappear entirely when these are destroyed. We have fifteen species in Britain, but about half of them are of the greatest rarity. There are about 600 species known at present; New Zealand has produced the greatest variety of forms; the forests of Teneriffe are rich in the genus _Tarphius_. The sedentary lives of many of these beetles are very remarkable; the creatures concealing themselves in the crannies of fungus-covered wood, and scarcely ever leaving their retreats, so that it is the rarest circumstance to find them at any distance from their homes. _Langelandia anophthalma_ lives entirely underground and is quite blind, the optic lobes being absent. Some Colydiidae are more active, and enter the burrows of wood-boring Insects to destroy the larvae (_Colydium_). Few of the larvae are known; but all appear to have the body terminated by peculiar hard corneous processes, as is the case with a great variety of Coleopterous larvae that live in wood.[117]
{234}FAM. 31. RHYSODIDAE.—_Tarsi four-jointed; mouth-parts covered by the large mentum; front tibiae notched on the inner edge._ This family consists only of a few species, but is found nearly all over the world in the warm and temperate regions. In many of their characters they resemble the Adephaga, but are very different in appearance and in the mouth. The larvae are not known. Some authorities think these Insects should be placed in the series Adephaga,[118] but it is more probable that they will prove to be amongst the numerous aberrant forms of Coleoptera that approach the various large natural series, without really belonging to them. The three families, Colydiidae, Cucujidae, and Rhysodidae, exhibit relations not only with other families of the Coleoptera Polymorpha, but also with most of the great series; Adephaga, Rhynchophora, Phytophaga, and Heteromera, being each closely approached.
FAM. 32. CUCUJIDAE.—_Tarsi five- or four-jointed, the first joint often short: antennae sometimes clubbed, but more often quite thin at the tip; front and middle coxae deeply embedded, globular, but with an angular prolongation externally; abdomen with five visible ventral segments, all movable._ This family and the Cryptophagidae are amongst the most difficult families to define; indeed it is in this portion of the Clavicorns that an extended and thorough study is most urgently required. The Cucujidae include a great diversity of forms; they are mostly found under the bark of trees, and many of them are very flat. Many of the larvae are also very flat, but Ferris says there is great diversity in their structure: they are probably chiefly carnivorous. There are about 400 species described; we have nearly a score in Britain.
[Illustration: Fig. 115—_Brontes planatus._ Britain. A, Larva; B, pupa; C, perfect Insect. (A and B after Perris.)]
The family Cupesidae of certain taxonomists must be at present associated with Cucujidae, though the first joint of the tarsus is elongate.
{235}FAM. 33. CRYPTOPHAGIDAE.—_Front and middle coxae very small and deeply embedded; antennae with enlarged terminal joints; tarsi five-jointed, the posterior sometimes in the male only four-jointed; abdomen with five visible ventral segments, capable of movement, the first much longer than any of the others._ A small family composed of obscure forms of minute size, which apparently have mould-eating habits, though very little is known on this point and several of the genera (_Antherophagus_, _Telmatophilus_) are found chiefly on growing plants, especially in flowers. Although the imago of _Antherophagus_ lives in flowers, yet the larva has only been found in the nests of bumble-bees; there is reason for believing that the imago makes use of the bee to transport it from the flowers it haunts to the nests in which it is to breed;[119] this it does by catching hold of the bee with its mandibles when the bee visits the flower in which the beetle is concealed. It is strange the beetle should adopt such a mode of getting to its future home, for it has ample wings. We must presume that its senses and instinct permit it to recognise the bee, but do not suffice to enable it to find the bee's nest. Some of the larvae of the genus _Cryptophagus_ are found abundantly in the nests of various wasps, where they are probably useful as scavengers, others occur in the nests of social caterpillars, and they are sometimes common in loose straw; this being the habitat in which Perris found the one we figure.
[Illustration: Fig. 116—_Cryptophagus dentatus._ Britain. A, Larva (after Perris); B, perfect Insect.]
FAM. 34. HELOTIDAE.—_Front and middle coxal cavities round, with scarcely any angular prolongation externally; all the coxae widely separated; five visible ventral segments, all mobile._ The Insects of this family are closely allied to Trogositidae and Nitidulidae, and have the tarsal structure of the former family; but the Helotidae are different in appearance from any members of either of these two families, and are readily distinguished by the coxal character. They are frequently classified with the Erotylidae, from which they differ by the differently shaped feet, especially by the diminished basal joint. {236}There is but one genus, and for a long time only two or three species were known, and were great rarities in collections; in the last few years the number has been raised to nearly forty.[120] They are remarkable beetles with oblong form, and a somewhat metallic upper surface, which is much sculptured, and possesses four yellow, smooth spots on the elytra. According to Mr. George Lewis they are found feeding at the running sap of trees, but the larvae are not known. Helotidae are peculiar to the Indo-Malayan region (including Japan) with one species in Eastern Africa.
FAM. 35. THORICTIDAE.—_Tarsi five-jointed, none of the joints broad; front coxae small, rather prominent, but not at all transverse; five visible ventral plates, all mobile; metasternum very short; antennae short, with a solid club._ This little family, consisting of the genus _Thorictus_, appears to be a distinct one, though the structure has only been very imperfectly studied. It is peculiar to the Mediterranean region, where the species live in ants' nests. They appear to be on terms of great intimacy with the ants; a favourite position of the beetle is on the scape of the antenna of an ant; here it hooks itself on firmly, and is carried about by the ant. Like so many other ants'-nest beetles, Thorictidae possess tufts of golden hair, which secrete some substance, the flavour of which is appreciated by the ants; these tufts in Thorictidae are situated either at the hind angles of the pronotum, or on the under surface of the body on each side of the breast; Wasmann thinks that when the beetles are riding about, as above described, the ants have then an opportunity of getting at the patches on the under surface.
[Illustration: Fig. 117—_Tritoma bipustulata._ Erotylidae. Britain. A, Larva (after Perris); B, perfect Insect.]
FAM. 36. EROTYLIDAE.—_Tarsi five-jointed, but with the fourth usually very small, the first three more or less broad and pubescent beneath. Antennae strongly clubbed. Front and middle coxal acetabula round, without angular prolongation externally; five visible ventral segments._ This is now a large and important family of about 1800 species, but it is chiefly exotic and tropical, its members haunting the fungoid growths {237}in forests. We have only six species in Britain, and the whole of Europe has only about two dozen, most of them insignificant (and in the case of the Dacnides aberrant, approaching the Cryptophagidae very closely). The sub-family Languriides (quite wanting in Europe) consists of more elongate Insects, with front acetabula open behind; they have different habits from Erotylides proper; some are known to live as larvae in the stems of herbaceous plants. They possess a highly developed stridulating organ on the front of the head. The Clavicorn Polymorpha are very closely connected with the Phytophaga by Languriides.
FAM. 37. MYCETOPHAGIDAE.—_Tarsi four-jointed, slender, the front feet of the male only three-jointed; coxae oval, not deeply embedded; abdomen with five ventral segments, all movable._ A small family, of interest chiefly because of the anomaly in the feet of the two sexes, for which it is impossible to assign any reason. The species are small, uninteresting Insects that live chiefly on Cryptogams of various kinds, especially in connection with timber; the larvae being also found there. There are about a dozen species in Britain, and scarcely 100 are described from all the world. The Diphyllides, placed by Leconte and Horn in this family, seem to go better in Cryptophagidae.
[Illustration: Fig. 118—_Litargus bifasciatus._ Mycetophagidae. Britain. A, Larva (after Perris); B, perfect Insect.]
FAM. 38. COCCINELLIDAE (_Lady-birds_).—_Tarsi apparently three-jointed; the first two joints pubescent beneath; the third joint consisting really of two joints, the small true third joint being inserted near the base of the second joint, the upper surface of which is grooved to receive it. Head much concealed by the thorax. Antennae feebly clubbed._ The lady-birds number fully 2000 species. The structure of their feet distinguishes them from nearly all other Coleoptera except Endomychidae, which are much less rotund in form, and have larger antennae. One genus of Endomychids—_Panomoea_—bears, however, a singular resemblance to lady-birds, both in form and style of coloration. Several species of Coccinellidae are remarkable on account of the numerous variations in colour they present. Coccinellidae frequently multiply to an enormous extent, and are of great value, as they destroy wholesale the plant-lice, scale-Insects, {238}and Acari that are so injurious to cultivated plants. They also eat various other soft-bodied Insects that attack plants. As they are excessively voracious, and are themselves singularly free from enemies and multiply with great rapidity, all these features of their economy render them of inestimable value to the agriculturist and horticulturist. The species of the sub-family Epilachnides feed on plants, and one or two are occasionally injurious. The body-fluid of Coccinellidae has an unpleasant odour and taste. Many lady-birds have the power of exuding, when disturbed, small quantities of a yellow fluid. Lutz has shown that this is not a special secretion, but an exudation of the fluid of the body that takes place through a small orifice at the tip of the tibia, from pressure caused by contraction of the body and limb.[121]
The larvae are much more active than beetle-larvae usually are, and many of them are very conspicuous when running about on plants to hunt their prey. They usually cast their skins three times, and sometimes concomitantly change a good deal in colour and form; the larval life does not usually exceed four or five weeks; at the end of which time the larva suspends itself by the posterior extremity, which is glued by a secretion to some object; the larval skin is pushed back to the anal extremity, disclosing the pupa; this differs in several respects from the usual pupa of beetles; it is harder, and is coloured, frequently conspicuously spotted, and dehisces to allow the escape of the beetle, so that the metamorphosis is altogether more like that of Lepidoptera than that of Coleoptera. There is much variety in the larvae; some of them bear large, complexly-spined, projections; those of the group Scymnites have small depressions on the surface, from which it has been ascertained that waxy secretions exude; but in _Scymnus minimus_ no such excretions are formed. Certain species, when pupating, do not shuffle the skin to the extremity of the body, but retain it as a covering for the pupa. The larvae that feed on plants are much less
## active than the predaceous forms. We are well supplied with Coccinellidae
in Britain, forty species being known here.
The systematic position of Coccinellidae amongst the Coleoptera has been for long a moot point. Formerly they were associated with various other beetles having three-jointed, or apparently three-jointed, feet, as a series with the name Trimera, or {239}Pseudotrimera. But they are generally placed in the Clavicorn series, near Endomychidae. Verhoeff has recently made considerable morphological studies on the male genital organs of Coleoptera, and as the result, he concludes that Coccinellidae differ radically from all other Coleoptera as regards these structures, and he therefore treats them as a distinct series or sub-order, termed Siphonophora. The genus _Lithophilus_ has been considered doubtfully a member of Coccinellidae, as the tarsi possess only in a slight degree the shape characteristic of the family: Verhoeff finds that they are truly Coccinellidae, forming a distinct division, Lithophilini; and our little species of _Coccidula_, which have somewhat the same appearance as Lithophilini, he treats as another separate group, Coccidulini.
FAM. 39. ENDOMYCHIDAE.[122]—_Tarsi apparently three-jointed, the first two joints broad, the terminal joint elongate; at the base of the terminal joint there is, however, a very small joint, so that the tarsi are pseudotetramerous; antennae rather large, with a large club; labium not at all retracted behind the mentum; front and middle coxae globose; abdomen with five movable ventral segments, and a sixth more or less visible at the tip._ This family includes a considerable diversity of elegant Insects that frequent fungoid growths on wood. It comprises at present fully 500 species, but nearly the whole of them are exotic, and inhabit the tropical forests. We have only two British species, both of which are now rarities, but apparently were much commoner at the beginning of the century. The larvae are broader than is usual in Coleoptera; very few, however, are known.
[Illustration: Fig. 119—_Mycetaea hirta._ Britain. A, Larva (after Blisson); B, perfect Insect.]
FAM. 40. MYCETAEIDAE.—_Tarsi four-jointed, the first two joints not very different from the third, usually slender; abdomen with five visible ventral segments, which are movable; front and middle coxae globular._ The little Insects composing this family are by many placed as a division of Endomychidae, and Verhoeff is of opinion that the group is an altogether artificial one; but we think, with Duval, it makes matters simpler to separate them. There are only {240}some forty or fifty species, found chiefly in Europe and North America. We have three in Britain; one of these, _Mycetaca hirta_ is very common, and may be found in abundance in cellars in the heart of London, as well as elsewhere; it is said to have injured the corks of wine-bottles, and to have caused leakage of the wine, but we think that it perhaps only increases some previous deficiency in the corkage, for its natural food is fungoid matters. The larva is remarkable on account of the clubbed hairs at the sides of the body.
FAM. 41. LATRIDIIDAE.—_Tarsi three-jointed; anterior coxal cavities round, not prolonged externally; abdomen with five visible and mobile ventral segments._ Very small Insects, species of which are numerous in most parts of the world, the individuals being sometimes very abundant. The larvae (Fig. 120, A) are said by Perris to have the mandibles replaced by fleshy appendages. The pupa of _Latridius_ is remarkable, on account of the numerous long hairs with heads instead of points; the larva of _Corticaria_ is very like that of _Latridius_, but some of the hairs are replaced by obconical projections. The sub-family Monotomides is by many treated as a distinct family; they have the elytra truncate behind, exposing the pygidium, and the coxae are very small and very deeply embedded. Most of the Latridiidae are believed to live on fungoid matters; species of _Monotoma_ live in ants' nests, but probably have no relations with the ants. A few species of Latridiides proper also maintain a similar life; _Coluocera formicaria_ is said to be fond of the stores laid up by _Aphaenogaster structor_ in its nests. About 700 species are now known; scarcely any of the individuals are more than one-tenth of an inch long. We have about 40 species in Britain. The North American genus _Stephostethus_ has the prosternum constructed behind the coxae, somewhat in the same manner as it is in the Rhynchophorous series of Coleoptera.
[Illustration: Fig. 120—_Latridius minutus._ Britain. A, Larva (after Perris); B, perfect Insect.]
FAM. 42. ADIMERIDAE.—_Tarsi appearing only two-jointed, a broad basal joint and an elongate claw-bearing joint, but between the two there are two very small joints._ This family consists only of the American genus _Adimerus_; nothing is known of {241}the life-history of these small Insects. They are of some interest, as this structure of the foot is not found in any other beetles.
[Illustration: Fig. 121—_Adimerus setosus._ Adimeridae. A, the Insect; B, one foot more enlarged. Mexico. From _Biol. Centr. Amer. Col._ ii. pt. i.]
[Illustration: Fig. 122—_Tiresias serra._ Larva. New Forest.]
FAM. 43. DERMESTIDAE.—_Tarsi five-jointed; antennae usually short, with the club frequently very large in proportion, and with the under side of the thorax bearing a hollow for its reception. Front coxae rather long, oblique: hind coxa formed to receive the femur when in repose._ A family of 300 or 400 species of small or moderate-sized beetles; the surface, usually covered with fine hair, forming a pattern, or with scales. _Byturus_, the position of which has long been disputed, has now been placed in this family; it has a more imperfectly formed prosternum, and the third and fourth joints of the tarsi are prolonged as membranous lobes beneath; the hind coxae leave the femora quite free. Dermestidae in the larval state nearly all live on dried animal matter, and are sometimes very destructive; some of them totally destroy zoological collections. They are very remarkable on account of the complex clothing of hairs they bear; they have good powers of locomotion, and many of them have a peculiar gait, running for a short distance, then stopping and vibrating some of their hairs with extreme rapidity. They exhibit great variety of form. Many of them are capable of supporting life for long periods on little or no food, and in such cases moult an increased number of times: pupation takes place in the larval skin. _Anthrenus fasciatus_ has been reared in large numbers on a diet of dried horse-hair in furniture. The young larva of this species observed by the writer did not possess the remarkable, complex arrangement of hairs that appeared when it was further grown. The most curious of Dermestid larvae is that of _Tiresias serra_, which lives amongst cobwebs in {242}old wood, and probably feeds on the remains of Insects therein, perhaps not disdaining the cobwebs themselves. Attention has been frequently called to the hairs of the larvae of these Insects, but they have never been adequately discussed, and their function is quite unknown.
FAM. 44. BYRRHIDAE (_Pill-beetles_).—_Oval or round, convex beetles; tarsi five-jointed, front coxae not exserted, transverse; hind coxa shielding the retracted femur. The whole of the appendages capable of a complete apposition to the body._ Although a small family of only 200 or 300 species, Byrrhidae are so heterogeneous that no characteristic definition that will apply to all the sub-families can be framed. Very little is known as to their life-histories. _Byrrhus pilula_ is one of our commonest beetles, and may be found crawling on paths in early spring even in towns; it moves very slowly, and when disturbed, at once contracts the limbs so completely that it looks like an inanimate object. The larva is cylindrical, soft; the prothoracic and last two abdominal segments are larger than the others, the last bearing two pseudopods; its habits are unknown, and no good figure exists of it.
The chief groups of Byrrhidae are Nosodendrides, Byrrhides (including Amphicyrtides), Limnichides, and Chelonariides. The first consists of species frequenting the exuding sap of trees; they have an unusually large mentum, abruptly clubbed antennae, and the head cannot be retracted and concealed. The genus _Nosodendron_ seems to be distributed over a large part of the world. The Byrrhides have the antennae gradually thicker towards the tip, the mentum small, and the head and thorax so formed that the former can be perfectly retracted. The species are rather numerous, and are found in the northern and antipodeal regions, being nearly completely absent from the tropics. The Limnichides are minute Insects living in very moist places; they have small delicate antennae, which are imperfectly clubbed. The group is very widely distributed.
The Chelonariides are a very peculiar form of Coleoptera: oval Insects of small size with the prothorax so formed that the head can be withdrawn under (rather than into) it, and then abruptly inflexed, so that the face then forms part of the under surface: the antennae have the basal three joints thicker than the others; these being not in the least clubbed, but having the {243}joints so delicately connected that the organs are rarely unmutilated. The modifications of the head and prothorax are quite unlike those of other Byrrhidae, and if the Chelonariides do not form a distinct family, they should be associated with Dascillidae. Nothing is known as to the earlier stages. They are chiefly tropical Insects, though one species is found in North America.
FAM. 45. CYATHOCERIDAE.—_Minute Insects of broad form; parts of the mouth concealed; antennae four-jointed; tarsi not divided into joints; prosternum small._ The only species of this aberrant family, _Cyathocerus horni_, has been found in Central America. Nothing is known as to its life-history.
FAM. 46. GEORYSSIDAE.—_Antennae short, clubbed; tarsi four-jointed; prosternum very small; front coxae exserted, but not contiguous._ There are about two dozen species of these small beetles known. Our British _Georyssus pygmaeus_ lives in extremely wet places, and covers itself with a coating of mud or fine sand so that it can only be detected when in movement. Nothing further is known as to its life-history or habits. Members of the genus have been detected in widely-separated parts of the globe.
FAM. 47. HETEROCERIDAE.—_Labrum and mandibles projecting forwards; antennae short, the terminal seven joints broad and short, forming a sort of broad serrate club; legs armed with stout spines; tarsi four-jointed._ The Heteroceridae are small beetles covered with very dense but minute pubescence; they live in burrows among mud or sand in wet places, and are found in many parts of the world. They possess a stridulating organ in the form of a slightly elevated curved line on each side of the base of the abdomen, rubbed by the posterior femur. The larvae live in the same places as the beetles; they have well-developed thoracic legs, the mandibles are porrect, the three thoracic segments rather large, and the body behind these becomes gradually narrower; they are believed to eat the mud amongst which they burrow. We have seven British species of Heteroceridae.
FAM. 48. PARNIDAE.—_Prosternum distinct in front of the coxae, usually elongate, behind forming a process received into a definite cavity on the mesosternum; head retractile, the mouth protected by the prosternum. Tarsi five-jointed, terminal joint long._ {244}Although the characters of these Insects are not very different from those of Byrrhidae, of Dascillidae, and even of certain Elateridae, there is practically but little difficulty in distinguishing Parnidae. They are of aquatic habits, though many, in the perfect state, frequently desert the waters. There are about 300 or 400 species known, but the family is doubtless more extensive, as these small beetles attract but little notice. There are two groups:—1. Parnides, in which the front coxae have a considerable transverse extension, the antennae are frequently short and of peculiar structure, and the body is usually clothed with a peculiar, dense pubescence. 2. Elmides, with round front coxae, a bare, or feebly pubescent body, and simple antennae. _Parnus_ is a genus commonly met with in Europe, and is less aquatic in habits than its congeners; it is said to enter the water carrying with it a coating of air attached to its pubescence. Its larvae are not well known; they live in damp earth near streams, and are said to much resemble the larvae of Elateridae. _Potamophilus acuminatus_ has a very interesting larva, described by Dufour; it lives on decaying wood in the Adour. It is remarkable from the ocelli being arranged so as to form an almost true eye on each side of the head; there are eight pairs of abdominal spiracles, and also a pair on the mesothorax, though there are none on the pro- or meta-thorax; each of the stigmata has four elongate sacs between it and the main tracheal tube; the body is terminated by a process from which there can be protruded bunches of filamentous branchiae. The larvae of _Macronychus quadrituberculatus_ is somewhat similar, though the features of its external structure are less remarkable. The Elmides live attached to stones in streams; the larva is rather broad, fringed at the sides of the body, and bears behind three elegant sets of fine filamentous branchiae. The North American genus _Psephenus_ is placed in Parnidae, though instead of five, the male has seven, the female six, visible ventral segments; the larva is elliptical, with dilated margins to the body. Friederich, has given,[123] without mentioning any names, a detailed account of Brazilian Parnid larvae, that may perhaps be allied to _Psephenus_.
FAM. 49. DERODONTIDAE.—_Tarsi five-jointed, slender, fourth joint rather small; front coxae prominent and transversely {245}prolonged; middle coxae small; abdomen with five visible segments, all mobile, the first not elongated._ One of the smallest and least known of the families of Coleoptera; it consists of four or five species of small Insects of the genera _Derodontus_ and _Peltasticta_, found in North America, Europe, and Japan. The distinction of the family from Cleridae is by no means certain; our European _Laricobius_ apparently possessing characters but little different. Nothing is known as to the life-histories.
FAM. 50. CIOIDAE.—_Small or minute beetles; antennae short, terminal joints thicker; tarsi short, four-jointed; anterior and middle coxae small, oval, deeply embedded; abdomen with five ventral segments, all mobile._ The position of these obscure little Insects seems to be near Colydiidae and Cryptophagidae, though they are usually placed near Bostrichidae. So far as known, they all live in fungi, or in wood penetrated by fungoid growths. The cylindrical larvae live also in similar matter; they usually have the body terminated behind by one or two hooks curved upwards; that of _Cis melliei_ (Fig. 124) has, instead of these hooks, a curious chitinous tube. About 300 species of the family are now known; a score, or so, occurring in Britain. The Hawaiian Islands have a remarkably rich and varied fauna of Cioidae.
[Illustration: Fig. 123—_Derodontus maculatus._ North America.]
[Illustration: Fig. 124—_Cis melliei._ Martinique. A, Perfect Insect; B, pupa; C, larva; D, terminal portion of body of larva. (After Coquerel.)]
FAM. 51. SPHINDIDAE.—This family of half a dozen species of rare and small Insects, differs from Cioidae by the tarsi being five-jointed at any rate on the front and middle feet, opinions differing as to whether the number of joints of the hind tarsi is four or five. These Insects live in fungi growing in wood, _e.g._ _Reticularia hortensis_, that are at first pulpy and {246}afterwards become powder. The larvae of both of our British genera, _Sphindus_ and _Aspidiphorus_, have been described by Perris, who considers them allied to the fungivorous Silphidae and Latridiidae. The systematic position of these Insects has been the subject of doubt since the days of Latreille.
FAM. 52. BOSTRICHIDAE (APATIDAE of some authors).—_Tarsi five-jointed, but the first joint very short and imperfectly separated from the second; front coxae prominent, contiguous, very little extended transversely; five visible ventral segments._ The Bostrichidae attack dry wood, and sometimes in such large numbers that timber is entirely destroyed by them; most of them make cylindrical burrows into the wood. The larvae have the posterior part of the body incurved, and resemble the wood-boring larvae of Anobiidae rather than the predaceous larvae of Cleridae. We follow Leconte and Horn in placing Lyctides as a division of Bostrichidae; although differing very much in appearance, they have similar habits and larvae. The typical Bostrichides are remarkable for their variety of sculpture and for the shapes of the posterior part of the body; this part is more or less conspicuously truncate, and furnished with small prominences. _Dinapate wrightii_, found in the stems of a species of _Yucca_ in the Mojave desert of California, attains a length of nearly two inches; its larva is extremely similar to that of _A. capucina_. Some of the forms (_Phonapate_) stridulate in a manner peculiar to themselves, by rubbing the front leg against some projections at the hind angle of the prothorax. Upwards of 200 species of the family are known. In Britain we have only four small and aberrant forms.
[Illustration: Fig. 125—_Apate capucina._ Europe. A, Larva (after Perris); B, perfect Insect.]
FAM. 53. PTINIDAE.—_Tarsi five-jointed, first joint not reduced in size, often longer than second; front and middle coxae small, not transversely extended, the former slightly prominent; five visible ventral segments; prosternum very short._ Here are included two sub-families, Ptinides and Anobiides; they are considered as distinct families by many authors, but in the present imperfect state of knowledge[124] it is not necessary to treat them separately.
{247}[Illustration: Fig. 126—"Biscuit-weevil." _Anobium paniceum._]
[Illustration: Fig. 127.—Early stages of _Anobium paniceum_. A, Eggs, variable in form; B, larva; C, pupa; D, asymmetrical processes terminating body of pupa. [This larva is probably the "book-worm" of librarians].]
Ptinidae are sometimes very destructive to dried animal matter, and attack specimens in museums; Anobiides bore into wood, and apparently emerge as perfect Insects only for a very brief period; _Anobium_ (_Sitodrepa_) _paniceum_ is, however, by no means restricted in its tastes; it must possess extraordinary powers of digestion, as we have known it to pass several consecutive generations on a diet of opium; it has also been reported to thrive on tablets of dried compressed meat; in India it is said to disintegrate books; a more usual food of the Insect is, however, hard biscuits; weevilly biscuits are known to every sailor, and the so-called "weevil" is usually the larva of _A. paniceum_ (Fig. 127, B). In the case of this Insect we have not detected more than one spiracle (situate on the first thoracic segment); the other known larvae of Anobiides are said to possess eight abdominal spiracles. The skeleton in some of this sub-family is extremely modified, so as to allow the Insects to pack themselves up in repose; the head is folded in over the chest, and a cavity existing on the breast is thus closed by the head; in this cavity the antennae and the prominent mouth-parts are received and protected; the legs shut together {248}in an equally perfect manner, so that no roughness or chink remains, and the creature looks like a little hard seed. _Anobium striatum_ is a common Insect in houses, and makes little round holes in furniture, which is then said to be "worm-eaten." _A._ (_Xestobium_) _tessellatum_, a much larger Insect, has proved very destructive to beams in churches, libraries, etc. These species are the "death-watches" or "greater death-watches" that have been associated with the most ridiculous superstitions (as we have mentioned in Volume V., when speaking of the lesser death-watches, or Psocidae). The ticking of these Insects is really connected with sex, and is made by striking the head rapidly against the wood on which the Insect is standing.
The very anomalous genus _Ectrephes_ (Fig. 128) is found in ants' nests in Australia. Westwood placed it in Ptinidae. Wasmann has recently treated it as a distinct family, Ectrephidae, associating it with _Polyplocotes_ and _Diplocotes_, and treating them as allied to Scydmaenidae.
[Illustration: Fig. 128—_Ectrephes kingi._ West Australia. (After Westwood.)]
FAM. 54. MALACODERMIDAE.—_Seven (or even eight) visible ventral segments, the basal one not co-adapted in form with the coxae; tarsi five-jointed. Integument softer than usual, the parts of the body not accurately co-adapted._ This important family includes a variety of forms: viz. Lycides, Drilides, Lampyrides, Telephorides; though they are very different in appearance, classifiers have not yet agreed on separating them as families. Of these the Lampyrides, or glow-worms, are of special interest, as most of their members give off a phosphorescent light when alive; in many of them the female is apterous and like a larva, and then the light it gives is usually conspicuous, frequently much more so than that of its mate; in other cases the males are the most brilliant. The exact importance of these characters in the creatures' lives is not yet clear, but it appears probable that in the first class of cases the light of the female serves as an attraction to the male, while in the second class the very brilliant lights of the male serve as an amusement, or as an incitement to rivalry amongst the individuals of this sex.
{249}[Illustration: Fig. 129—_Phengodes hieronymi._ Cordoba, South America. (After Haase.) A, Male; B, female. _l_, _l_, Positions of luminous spots; _ls_, spiracles. About × 3.]
The well-known fire-flies (_Luciola_) of Southern Europe are an example of the latter condition. They are gregarious, and on calm, warm nights crowds of them may be seen moving and sparkling in a charming manner. These individuals are all, or nearly all, males; so rare indeed is the female that few entomologists have even noticed it. The writer once assisted in a large gathering of _Luciola italica_ in the Val Anzasca, which consisted of many hundreds of specimens; all of those he caught, either on the wing or displaying their lights on the bushes, were males, but he found a solitary female on the ground. This sex possesses ordinary, small eyes instead of the large, convex organs of the male, and its antennae and legs are much more feeble, so that though provided with elytra and wings it is altogether a more imperfect creature. Emery has given an account of his observations and experiments on this Insect, but they do not give any clear idea as to the exact function of the light.[125] In our British glow-worm the female is entirely apterous—hence the name glow-worm—but the male has elytra and ample wings, and frequently flies at night into lighted apartments. Although so little has been ascertained as to the light of Lampyridae, there are two facts that justify us in supposing that it is in some way of importance to the species. These are: (1) that in a great many species the eyes have a magnificent and unusual development; (2) that the habits of the creatures are in nearly all cases nocturnal. It is true that the little _Phosphaenus hemipterus_ is said to be diurnal in habits, but it is altogether an exceptional form, being destitute of wings in both sexes, and possessed of only very feeble light-giving powers, and we have, moreover, very little real knowledge as to its natural history; it is said {250}that the female is of the utmost rarity, though the male is not uncommon.
The nature of the luminosity of _Lampyris_ has given rise to many contradictory statements; the light looks somewhat like that given off by phosphorus, and is frequently spoken of as phosphorescence; but luminescence is a better term. The egg, larva, pupa, and male are luminous as well as the female (at any rate in _L. noctiluca_); the luminescence is, however, most marked in the female imago, in which it is concentrated near the extremity of the abdomen; here there are two strata of cells, and many fine capillary tracheae are scattered through the luminous substance. Wielowiejski concludes that the light-producing power is inherent in the cells of the luminous organ, and is produced by the slow oxidation of a substance formed under the influence of the nervous system. The cells are considered to be essentially similar to those of the fat-body.[126] The luminescence of Lampyridae is very intermittent, that is to say, it is subject to rapid diminutions and increases of its brilliancy; various reasons have been assigned for this, but all are guesses, and all that can be said is that the changes are possibly due to diminution or increase of the air-supply in the luminous organ, but of the way in which this is controlled there seems to be no evidence. Considerable difference of opinion has existed as to the luminescence of the eggs of _Lampyris_. If it exist in the matter contained in the egg, it is evident that it is independent of the existence of tracheae or of a nervous system. Newport and others believed that the light given by the egg depended merely on matter on its exterior. The observations of Dubois[127] show, however, that it exists in the matter in the egg; he has even found it in the interior of eggs that had been deposited unfertilised.
From time to time, since the commencement of the nineteenth century, there have appeared imperfect accounts of extraordinary light-giving larvae found in South America, of various sizes, but attaining in some cases a length, it is said, of three inches; they are reported as giving a strong red light from the two extremities of the body, and a green light from numerous points along the {251}sides of the body, and hence are called, it is said, in Paraguay the railway-beetle. We may refer the reader to Haase's paper[128] on the subject of these "larvae," as we can here only say that it appears probable that most of these creatures may prove to be adult females of the extraordinary group Phengodini, in which it would appear that the imago of the female sex is in a more larva-like state than it is in any other Insects. The males, however, are well-developed beetles; unlike the males of Lampyrides, in general they have not peculiar eyes, but on the other hand they possess antennae which are amongst the most highly developed known, the joints being furnished on each side with a long appendage densely covered with pubescence of a remarkable character. There is no reason to doubt that Haase was correct in treating the Insect we figure (Fig. 129, B) as a perfect Insect; he is, indeed, corroborated by Riley.[129] The distinctions between the larva and female imago are that the latter has two claws on the feet instead of one, a greater number of joints in the antennae, and less imperfect eyes; the female is in fact a larva, making a slightly greater change at the last ecdysis, than at those previous. It is much to be regretted that we have so very small a knowledge of these most interesting Insects. Malacodermidae are probably the most imperfect or primitive of all beetles, and it is a point of some interest to find that in one of them the phenomena of metamorphosis are reduced in one sex to a minimum, while in the other they are—presumably at least—normal in character.
Numerous larvae of most extraordinary, though diverse, shapes, bearing long processes at the sides of the body, and having a head capable of complete withdrawal into a slender cavity of the thorax, have long been known in several parts of the world, and Dr. Willey recently found in New Britain a species having these body-processes articulated. Though they are doubtless larvae of Lampyrides, none of them have ever been reared or exactly identified.
A very remarkable Ceylonese Insect, _Dioptoma adamsi_ Pascoe, is placed in Lampyrides, but can scarcely belong there, as apparently it has but five or six visible ventral segments; this Insect has two pairs of eyes, a large pair, with coarse facets on {252}the under side of the head, and a moderate-sized pair with fine facets on the upper side. Nothing is known as to the habits of this curiosity, not even whether it is luminous in one or both sexes.
It is believed that the perfect instar of Lampyrides takes no food at all. The larvae were formerly supposed to be vegetarian, but it appears probable that nearly all are carnivorous, the chief food being Mollusca either living or dead. The larvae are active, and in many species look almost as much like perfect Insects as do the imagos.
The other divisions of Malacodermidae—Lycides, Drilides, Telephorides—also have predaceous, carnivorous larvae. All these groups are extensive. Though much neglected by collectors and naturalists, some 1500 species of the family Malacodermidae have been detected. We have about 50 in Britain, and many of them are amongst the most widely distributed and abundant of our native Insects. Thus, however near they may be to the primitive condition of Coleoptera, it is highly probable that they will continue to exist alongside of the primitive Cockroaches and Aptera, long after the more highly endowed forms of Insect-life have been extinguished wholesale by the operations of mankind on the face of the earth.
[Illustration: Fig. 130—_Malachius aeneus._ Britain. A, Larva (after Perris); B, female imago.]
FAM. 55. MELYRIDAE (or MALACHIIDAE).—_Six visible and moveable ventral abdominal segments; the basal part more or less distinctly co-adapted with the coxae._ These Insects are extremely numerous, but have been very little studied. In many works they are classified with Malacodermidae, but were correctly separated by Leconte and Horn, and this view is also taken by Dr. Verhoeff, the latest investigator. The smaller number of visible ventral segments appears to be due to a change at the base correlative with an adaptation between the base of the abdomen and the hind coxae. The characters are singularly parallel with those of Silphidae; but in Melyridae the antennae are filiform or serrate, {253}not clavate. The habits in the two families are different, as the Melyridae are frequenters of flowers. Many of the Melyridae have the integument soft, but in the forms placed at the end of the family—_e.g._ _Zygia_—they are much firmer. Thus these Insects establish a transition from the Malacodermidae to ordinary Coleoptera. Although the imagos are believed to consume some products of the flowers they frequent, yet very little is really known, and it is not improbable that they are to some extent carnivorous. This is the case with the larvae that are known (Fig. 130, larva of _Malachius aeneus_). These are said by Perris to bear a great resemblance to those of the genus _Telephorus_, belonging to the Malacodermidae.
FAM. 56. CLERIDAE.—_Tarsi five-jointed; but the basal joint of the posterior very indistinct, usually very small above, and closely united with the second by an oblique splice; the apices of joints two to four usually prolonged as membranous flaps; anterior coxae prominent, usually contiguous, rather large, but their cavities not prolonged externally; labial palpi usually with large hatchet-shaped terminal joint; ventral segments five or six, very mobile._ The Cleridae are very varied in form and colours; the antennae are usually more or less clubbed at the tip, and not at all serrate, but in _Cylidrus_ and a few others they are not clubbed, and in _Cylidrus_ have seven flattened joints. The student should be very cautious in deciding as to the number of joints in the feet in this family, as the small basal joint is often scarcely distinguishable, owing to the obliteration of its suture with the second joint. The little Alpine _Laricobius_ has the anterior coxal cavities prolonged externally, and the coxae receive the femora to some extent, so that it connects Cleridae and Derodontidae. The Cleridae are predaceous, and their larvae are very
## active; they are specially fond of wood-boring Insects; that of _Tillus
elongatus_ (Fig. 131) enters the burrows of _Ptilinus pectinicornis_ in search of the larva. The members of the group Corynetides frequent animal matter, carcases, bones, etc., and, it is said, feed thereon, but Perris's recent investigations[130] make it probable that the larvae really eat the innumerable Dipterous larvae found in such refuse; it is also said that the larvae of Cleridae spin cocoons for their metamorphosis; but Perris has also shown that the larvae of _Necrobia ruficollis_ really use the puparia formed {254}by Diptera. Some of the species of _Necrobia_ have been spread by commercial intercourse, and _N. rufipes_ appears to be now one of the most cosmopolitan of Insects. The beautifully coloured _Corynetes coeruleus_ is often found in our houses, and is useful, as it destroys the death-watches (_Anobium_) that are sometimes very injurious. _Trichodes apiarius_, a very lively-coloured red and blue beetle, destroys the larvae of the honey-bee, and Lampert has reared _Trichodes alvearius_ from the nests of _Chalicodoma muraria_, a mason-bee; he records that one of its larvae, after being full grown, remained twenty-two months quiescent and then transformed to a pupa. Still more remarkable is a case of fasting of the larva of _Trichodes ammios_ recorded by Mayet;[131] this Insect, in its immature form, destroys _Acridium maroccanum_; a larva sent from Algeria to M. Mayet refused such food as was offered to it for a period of two and a half years, and then accepted mutton and beef as food; after being fed for about a year and a half thereon, it died. Some Cleridae bear a great resemblance to Insects of other families, and it appears probable that they resemble in one or more points the Insects on which they feed. The species are now very numerous, about 1000 being known, but they are rare in collections; in Britain we have only nine species, and some of them are now scarcely ever met with.
[Illustration: Fig. 131—Larva of _Tillus elongatus_. (New Forest). A, Head; B, front leg; C, termination of the body, more magnified.]
FAM. 57. LYMEXYLONIDAE.—_Elongate beetles, with soft integuments, front and middle coxae exserted, longitudinal in position; tarsi slender, five-jointed; antennae short, serrate, but rather broad._ Although there are only twenty or thirty species of this family, they occur in most parts of the world, and are remarkable on account of their habit of drilling cylindrical holes in hard wood, after the manner of Anobiidae. The larva of _Lymexylon navale_ was formerly very injurious to timber used for constructing ships, but of late years its ravages appear to have been of little importance. The genus _Atractocerus_ consists of a few species of very abnormal {255}Coleoptera, the body being elongate and vermiform, the elytra reduced to small, functionless appendages, while the wings are ample, not folded, but traversed by strong longitudinal nervures, and with only one or two transverse nervures. Owing to the destruction of our forests the two British Lymexylonidae—_L. navale_ and _Hylecoetus dermestoides_—are now very rarely met with.
[Illustration: Fig. 132—_Hydrocyphon deflexicollis._ Britain. A, Larva (after Tournier); B, imago.]
FAM. 58. DASCILLIDAE.—_Small or moderate-sized beetles, with rather flimsy integuments, antennae either serrate, filiform, or even made flabellate by long appendages; front coxae elongate, greatly exserted; abdomen with five mobile ventral segments; tarsi five-jointed._ This is one of the most neglected and least known of all the families of Coleoptera, and one of the most difficult to classify; though always placed amongst the Serricornia, it is more nearly allied to Parnidae and Byrrhidae, that are placed in Clavicornia, than it is to any of the ordinary families of Serricornia. It is probable that careful study will show that it is not natural as at present constituted, and that the old families, Dascillidae and Cyphonidae, now comprised in it, will have to be separated. Only about 400 species are at present known; but as nearly 100 of these have been detected in New Zealand, and 17 in Britain, doubtless the numbers in other parts of the world will prove very considerable, these Insects having been neglected on account of their unattractive exterior, and fragile structure. The few larvae known are of three or four kinds. That of _Dascillus cervinus_ is subterranean, and is believed to live on roots; in form it is somewhat like a Lamellicorn larva, but is straight, and has a large head. Those of the Cyphonides are aquatic, and are remarkable for possessing antennae consisting of a great many joints (Fig. 132, A). Tournier describes the larva of _Helodes_ as possessing abdominal but not thoracic spiracles, and as breathing by coming to the surface of the water and carrying down a bubble of air adhering to the posterior part of the body; the larva of _Hydrocyphon_ (Fig. 132, A) {256}possesses several finger-like pouches that can be exstulpated at the end of the body. It is probable that these larvae are carnivorous. The imago of this Insect abounds on the bushes along the banks of some of the rapid waters of Scotland; according to Tournier, when alarmed, it enters the water and goes beneath it for shelter. The third form of larva belongs to the genus _Eucinetus_, it lives on fungoid matter on wood, and has ordinary antennae of only four joints.[132] It is very doubtful whether _Eucinetus_ is related to other Dascillidae; some authorities indeed place it in Silphidae.
FAM. 59. RHIPICERIDAE.—_Tarsi five-jointed, furnished with a robust onychium (a straight chitinous process bearing hairs) between the claws; antennae of the male bearing long processes, and sometimes consisting of a large number of joints. Mandibles robust, strongly curved, and almost calliper-like in form._ This small family of less than 100 species is widely distributed, though confined to the warmer regions of the earth, a single species occurring in the extreme south of Eastern Europe. Very little is known as to the natural history. The larva of _Callirhipis dejeani_ (Fig. 133, A) is described by Schiödte as hard, cylindrical in form, and peculiarly truncate behind, so that there appear to be only eight abdominal segments, the ninth segment being so short as to look like an operculum at the extremity of the body. It lives in wood.
[Illustration: Fig. 133—A, Larva of _Callirhipis dejeani_ (after Schiödte); B, _Rhipicera mystacina_ male, Australia; C, under side of its hind foot.]
{257}[Illustration: Fig. 134—_Athous rhombeus._ New Forest. A, Larva; B, female imago.]
FAM. 60. ELATERIDAE (_Click-beetles_).—_Antennae more or less serrate along the inner margin, frequently pectinate, rarely filiform. Front coxae small, spherical. Thorax usually with hind angles more or less prolonged backwards; with a prosternal process that can be received in, and usually can move in, a mesosternal cavity. Hind coxa with a plate, above which the femur can be received. Visible ventral segments usually five, only the terminal one being mobile. Tarsi five-jointed._ This large family of Coleoptera comprises about 7000 species. Most of them are readily known by their peculiar shape, and by their faculty of resting on the back, stretching themselves out flat, and then suddenly going off with a click, and thus jerking themselves into the air. Some, however, do not possess this faculty, and certain of these are extremely difficult to recognise from a definition of the family. According to Bertkau[133] our British _Lacon murinus_ is provided near the tip of the upper side of the abdomen with a pair of eversible glands, comparable with those that are better known in Lepidopterous larvae. He states that this Insect does not try to escape by leaping, but shams death and "stinks away" its enemy. The glands, it would appear, become exhausted after the operation has been repeated many times. The extent of the leap executed by click-beetles differs greatly; in some species it is very slight, and only just sufficient to turn the Insect right side up when it has been placed on its back. In some cases the Insects go through the clicking movements with little or no appreciable result in the way of consequent propulsion. Although it is difficult to look on this clicking power as of very great value to the Elateridae, yet their organisation is profoundly modified so as to permit its accomplishment. The junction of the prothorax with the after-body involves a large number of pieces which are all more or less changed, so that the joint is endowed with greater mobility than usual; while in the position of repose, on the other hand, the two parts are firmly locked together. The thoracic stigma is of a highly remarkable nature, and the extensive {258}membrane in which it is placed appears to be elastic. Although the mechanics of the act of leaping are still obscure, yet certain points are clear; the prosternal process possesses a projection, or notch, on its upper surface near the tip; as a preliminary to leaping, this projection catches against the edge of the mesosternal cavity, and as long as this position is maintained the Insect is quiescent; suddenly, however, the projection slips over the catch, and the prosternal process is driven with force and rapidity into the mesosternal cavity pressing against the front wall thereof, and so giving rise to the leap.
Several larvae are well known; indeed the "wire-worms" that are sometimes so abundant in cultivated places are larvae of Elateridae. In this instar the form is usually elongate and nearly cylindrical; the thoracic segments differ but little from the others except that they bear rather short legs; the skin is rather hard, and usually bears punctuation or sculpture; the body frequently terminates in a very hard process, of irregular shape and bearing peculiar sculpture on its upper surface, while beneath it the prominent anal orifice is placed: this is sometimes furnished with hooks, the function of which has not yet been observed. The majority of these larvae live in decaying wood, but some are found in the earth; as a rule the growth is extremely slow, and the life of the larva may extend over two or more years. Some obscurity has prevailed as to their food; it is now considered to be chiefly flesh, though some species probably attack decaying roots; and it is understood that wire-worms destroy the living roots, or underground stems, of the crops they damage. Various kinds of Myriapods (see Vol. V. p. 29) are often called "wire-worm," but they may be recognised by possessing more than six legs. The larvae of the genus _Cardiophorus_ are very different, being remarkably elongate without the peculiar terminal structure, but apparently composed of twenty-three segments.
The genus _Pyrophorus_ includes some of the most remarkable of light-giving Insects. There are upwards of 100 species, exhibiting much diversity as to the luminous organs; some are not luminous at all; but all are peculiar to the New World, with the exception that there may possibly be luminous species, allied to the American forms, in the Fiji Islands and the New Hebrides. In the tropics of America the _Pyrophorus_, or Cucujos, form one of the most remarkable of the natural phenomena. {259}The earliest European travellers in the New World were so impressed by these Insects that descriptions of their wondrous display occupy a prominent position in the accounts of writers like Oviedo, whose works are nearly 400 years old. Only one of the species has, however, been investigated. _P. noctilucus_ is one of the most abundant and largest of the _Pyrophorus_, and possesses on each side of the thorax a round polished space from which light is given forth; these are the organs called eyes by the older writers. Besides these two eye-like lamps the Insect possesses a third source of light situate at the base of the ventral surface of the abdomen; there is no trace of this latter lamp when the Insect is in repose; but when on the wing the abdomen is bent away from the breast, and then this source of light is exposed; hence, when flying, this central luminous body can be alternately displayed and concealed by means of slight movements of the abdomen. The young larva of _P. noctilucus_ is luminous, having a light-giving centre at the junction of the head and thorax; the older larva has also numerous luminous points along the sides of the body near the spiracles. It is remarkable that there should be three successive seats of luminescence in the life of the same individual. The eggs too are said to be luminous. The light given off by these Insects is extremely pleasing, and is used by the natives on nocturnal excursions, and by the women for ornament. The structure of the light-organs is essentially similar to that of the Lampyridae. The light is said to be the most economical known; all the energy that is used being converted into light, without any waste by the formation of heat or chemical rays. The subject has been investigated by Dubois,[134] who comes, however, to conclusions as to the physiology of the luminous processes different from those that have been reached by Wielowiejski and others in their investigations on Glow-worms. He considers that the light is produced by the reactions of two special substances, luciferase and luciferine. Luciferase is of the nature of an enzyme, and exists only in the luminous organs, in the form, it is supposed, of extremely minute granules. Luciferine exists in the blood; and the light is actually evoked by the entry of blood into the luminous organ.
We have given to this family the extension assigned to it by {260}Schiödte. Leconte and Horn also adopt this view, except that they treat Throscides as a distinct family. By most authors Eucnemides, Throscides, and Cebrionides are all considered distinct families, but at present it is almost impossible to separate them on satisfactory lines. The following table from Leconte and Horn exhibits the characters of the divisions so far as the imago is concerned:—
Posterior coxae laminate; trochanters small.
Labrum concealed; antennae somewhat distant from the eyes, their insertion narrowing the front Eucnemides.
Labrum visible, free; antennae arising near the eyes under the frontal margin Elaterides.
Labrum transverse, connate with the front.
Ventral segments six; claws simple; tibial spurs well developed. Cebrionides.
Ventral segments five; claws serrate; tibial spurs moderate. Perothopides.
Posterior coxae not laminate; trochanters of middle and posterior legs very long Cerophytides.
[Illustration: Fig. 135—Larva of _Fornax_ n. sp. Hawaii. A, Upper side; B, under side: _s_ _s_, position of spiracles; C, head more enlarged; D, under side of terminal segment; _a_, anus.]
Throscides are considered to be distinguished by the mesosternum being impressed on each side in front for the accommodation of the posterior face of the front coxae. The genus _Throscus_ has the antennae clavate. The classification of the Elaterides and these forms is a matter of the greatest difficulty, and, if the larvae are also considered, becomes even more complex. Cebrionid larvae are different from those of any of the other divisions, and possess laminate, not calliper-like, mandibles. The larvae of Eucnemides (Fig. 135) are very little known, but are highly remarkable, inasmuch as it is very difficult to find any mouth-opening in some of them, and they have no legs. The other divisions possess very few species compared with Elaterides. In Britain we have about sixty species of Elaterides, four of Throscides and three of Eucnemides; _Cerophytum_ was probably a native many years ago. Neither Perothopides {261}nor Cebrionides are represented in our fauna; the former of these two groups consists only of four or five North American species, and the Cerophytides are scarcely more numerous.
FAM. 61. BUPRESTIDAE.—_Antennae serrate, never elongate; prothorax fitting closely to the after-body, with a process received into a cavity of the mesosternum so as to permit of no movements of nutation. Five visible ventral segments, the first usually elongate, closely united with the second, the others mobile. Tarsi five-jointed, the first four joints usually with membranous pads beneath._ This family is also of large extent, about 5000 species being known. Many of them are remarkable for the magnificence of their colour, which is usually metallic, and often of the greatest brilliancy; hence their wing-cases are used by our own species for adornment. The elytra of the eastern kinds of the genus _Sternocera_ are of a very brilliant green colour, and are used extensively as embroidery for the dresses of ladies; the bronze elytra of _Buprestis (Euchroma) gigantea_ were used by the native chieftains in South America as leg-ornaments, a large number being strung so as to form a circlet. The integument of the Buprestidae is very thick and hard, so as to increase the resemblance to metal. The dorsal plates of the abdomen are usually soft and colourless in beetles, but in Buprestidae they are often extremely brilliant. The metallic colour in these Insects is not due to pigment, but to the nature of the surface. Buprestidae appear to enjoy the hottest sunshine, and are found only where there is much summer heat. Australia and Madagascar are very rich in species and in remarkable forms of the family, while in Britain we possess only ten species, all of which are of small size, and nearly all are excessively rare. The family is remarkably rich in fossil forms; no less than 28 per cent of the Mesozoic beetles found by Heer in Switzerland are referred to Buprestidae.
[Illustration: Fig. 136—A, Larva of _Euchroma goliath_ (after Schiödte); B, imago of _Melanophila decostigma_. Europe.]
The larvae (Fig. 136, A) find nourishment in living vegetable matter, the rule being that they form galleries in or under the {262}bark of trees and bushes, or in roots thereof; some inhabit the stems of herbaceous plants and one or two of the smaller forms have been discovered to live in the parenchyma of leaves. A few are said to inhabit dead wood, and in Australia species of _Ethon_ dwell in galls on various plants. Buprestid larvae are of very remarkable shape, the small head being almost entirely withdrawn into the very broad thorax, while the abdomen is slender.[135] A few, however, depart from this shape, and have the thoracic region but little or not at all broader than the other parts. The larvae of _Julodis_—a genus that inhabits desert or arid regions—are covered with hair; they have a great development of the mandibles; it is believed that they are of subterranean habits, and that the mandibles are used for burrowing in the earth. Only the newly hatched larva is, however, known.
SERIES IV. HETEROMERA.
_Tarsi of the front and middle legs with five, those of the hind legs with four, joints._
This series consists of some 14,000 or 15,000 species. Twelve or more families are recognised in it, but the majority of the species are placed in the one great family, Tenebrionidae. The number of visible ventral segments is nearly always five. Several of the families of the series are of doubtful validity; indeed beyond that of Tenebrionidae the taxonomy of this series is scarcely more than a convention. The larvae may be considered as belonging to three classes; one in which the body is cylindrical and smooth and the integument harder than usual in larvae; a second in which it is softer, and frequently possesses more or less distinct pseudopods, in addition to the six thoracic legs; and a third group in which hypermetamorphosis prevails, the young larvae being the creatures long known as Triungulins, and living temporarily on the bodies of other Insects, so that they were formerly supposed to be parasites.
{263}FAM. 62. TENEBRIONIDAE.—_Front coxae short, not projecting from the cavities, enclosed behind. Feet destitute of lobed joints. Claws smooth._ This is one of the largest families of Coleoptera, about 10,000 species being already known. A very large portion of the Tenebrionidae are entirely terrestrial, wings suitable for flight being absent, and the elytra frequently more or less soldered. Such forms are described in systematic works as apterous. Unfortunately no comprehensive study has ever been made of the wings or their rudiments in these "apterous forms."[136] it is probable that the wings, or their rudiments or vestiges, always exist, but in various degrees of development according to the species, and that they are never used by the great majority of the terrestrial forms. Many of the wood-feeding Tenebrionidae, and the genera usually placed at the end of the family, possess wings well adapted for flight. The apterous forms are chiefly ground-beetles, living in dry places; they are very numerous in Africa, California, and North Mexico. Their colour is nearly always black, and this is probably of some physiological importance; the integuments are thick and hard, and if the wing-cases are taken off, it will be found that they are usually more or less yellow on the inner face, even when jet-black externally; the external skeleton is very closely fitted together, the parts that are covered consisting of very delicate membrane; the transition between the hard and the membranous portions of the external skeleton is remarkably abrupt. These ground-Tenebrionidae form a very interesting study, though, on account of their unattractive appearance, they have not received the attention they deserve.
[Illustration: Fig. 137—_Tenebrio molitor._ Europe, etc. A, Larva (meal-worm); B, pupa (after Schiödte); C, imago.]
Many of the Tenebrionidae, notwithstanding their dark {264}colours, are diurnal in habits, and some of them run with extreme velocity in places so bare and desert that the means of existence of the Insects is a mystery. Most of the Tenebrionidae, however, shun the light. The food is usually vegetable matter, and it is apparently preferred in a very dry state. Mr. Gahan has recently recorded that in _Praogena_ the under surface of the head has the gular region striate for stridulating purposes. This is the only instance known of a voice-organ in this situation, and moreover is the only case in all the Tenebrionidae in which any sound-producing organ has been discovered. The larvae exhibit but little variety, they are elongate and cylindrical, with harder integument than is usual in Coleopterous larvae; they have six thoracic legs, and at the under side of the posterior extremity the anus serves as a very short pseudopod. The resemblance of these larvae to those of Elateridae is considerable; but though the body is terminated by one or two small processes, these never attain the complexity of the terminal segment of Elateridae. The common meal-worm—_i.e._ the larva of _Tenebrio molitor_—is a very characteristic example of the group. The pupae are remarkable on account of peculiar projections, of varied and irregular form, that exist on the sides of the abdominal segments. Britain is very poor in these Insects; our list of them scarcely attains the number of thirty species.
FAM. 63. CISTELIDAE.—_Claws comb-like._ The very obscure beetles forming this family are only separated from Tenebrionidae on account of their pectinate claws. About 500 species of Cistelidae are recorded; the early instars, so far as known, do not differ from those of Tenebrionidae; the larvae are believed to live on dead wood.
FAM. 64. LAGRIIDAE.—_Anterior coxal cavities closed, tips of the front coxae free, claws smooth, penultimate joint of the tarsi broader, pubescent beneath._ This family has very little to distinguish it from Tenebrionidae, and the group Heterotarsini appears to connect the two. It is a small family of about 200 species, widely distributed, and represented in Britain by one species, _Lagria hirta_. The early instars are similar to those of the Tenebrionidae, except that the larva is less retiring in its habits and wanders about on foliage: it is of broader form than that of most of the Tenebrionidae. The pupa has long projections at the sides of the abdominal segments.
{265}FAM. 65. OTHNIIDAE.—Only about ten species are known of this dubious family. They are small Insects with weak integument, and are said by Leconte and Horn to be distinguished from "degraded Tenebrionidae" by the more mobile abdominal segments, the hind-margins of which are semi-membranous. The antennae are of the clubbed shape, characteristic of "Clavicornia," but this also occurs in numerous undoubted Tenebrionidae. Species of _Othnius_ have been found in Japan and Borneo, as well as in North America. Nothing is known as to their metamorphoses.
FAM. 66. ÆGIALITIDAE.—_All the coxae very widely separated; no co-adaptation between the sides of the abdomen and the edges of the wing-cases; five ventral segments and tip of a sixth visible._ Two minute and rare Insects from North-West America constitute this family. It is distinguished from Pythidae by the minute front coxae, widely separated, completely closed in, and deeply embedded in the prosternum.
FAM. 67. MONOMMIDAE.—This is a small family of less than 100 species, the members of which have the details of their external structure much modified, permitting the Insect to pack itself up in repose in a very perfect manner. They are of small size and oval form; and are absent from Europe and the Antipodes. Nothing appears to be known as to the metamorphosis.
FAM. 68. NILIONIDAE.—_Broad, circular Heteromera, of moderate size, with the front coxae but little separated, and the anterior acetabula closed, though having the appearance of being open in consequence of the tips of the epimera being free. The inflexed portion of the wing-cases remarkably broad._ A small family of less than fifty species, found on fungi, chiefly in South America. The metamorphoses are not known. It is of very doubtful validity.
FAM. 69. MELANDRYIDAE.—_Head not constricted behind the eyes; anterior acetabula not closed; claws smooth. Prothorax broad behind._ These are loosely-fitted-together Insects, of moderate or small size, frequenting dry wood or fungi. About 200 species are known, found chiefly in temperate regions. The few described larvae are rather varied in their details and cannot be generalised at present. The characters of the members of this family require fresh investigation.
FAM. 70. PYTHIDAE.—Distinguished from Melandryidae by the {266}prothorax being narrow behind. This is a small family of about 100 species, found in temperate regions in connection with timber. The species of _Rhinosimus_ have the head prolonged in front of the antennae so as to form a beak. The larva of _Pytho depressus_ is flat and has parallel sides; the body is terminated by two widely-separated sharp processes. It is found occasionally under the bark of firs in Scotland.
FAM. 71. PYROCHROIDAE.—Differs from Melandryidae by the head forming a very narrow neck behind, and by the penultimate tarsal joints being broad. They are feeble Insects, though active on the wing. They are destitute of any of the various remarkable structures found in Mordellidae. Only about forty species are known, and the family is confined to the north temperate region, being best represented in Japan. _Pyrochroa rubens_ is common in some parts of England; the larva is found under the bark of tree-stumps; it is remarkably flat, and has the eighth abdominal segment unusually long, while the ninth terminates the body in the form of two long sharp processes.
FAM. 72. ANTHICIDAE.—_Head with an abrupt narrow neck; prothorax narrower than the elytra. Middle and hind coxae placed in definite acetabula. Claws simple._ These little Insects are numerous in species; they have little resemblance to Pyrochroidae, though the characters of the two families cause us to place them in proximity. There are about 1000 species known; though we have only about 12 in Britain, they are very numerous in the Mediterranean region. The family Pedilidae of Lacordaire and some others is now merged in Anthicidae. Thomson and Champion, on the other hand, separate some very minute Insects to form the family Xylophilidae, on account of certain differences in the form of the abdomen and tarsi. The Xylophilidae live in dead wood; the Anthicidae, on the surface of the earth, after the manner of ground-beetles; very little is, however, known as to their natural history.
FAM. 73. OEDEMERIDAE.—_Prothorax not forming sharp edges at the sides, head without a narrow neck. Penultimate tarsal joint broad; claws smooth._ These Insects usually have a feeble integument, and bear a certain resemblance to Malacodermidae. Less than 500 species are known, but they are widely distributed, and occur in both temperate and tropical regions. The larvae live in old wood. _Nacerdes melanura_ is common on our {267}coasts, where its larva lives in timber cast up by the sea, or brought down by floods, and it is able to resist immersion by the tide. It is remarkable from the possession of five pairs of dorsal false feet on the anterior segments, and two pairs on the ventral aspect. In _Asclera caerulea_ there are six dorsal and three ventral pairs of these remarkable pseudopods. We have six species of Oedemeridae in Britain, including _Asclera_ as well as _Nacerdes_.
[Illustration: Fig. 138—_Asclera caerulea._ A, Larva; B, pupa (after Schiödte); C, imago. Cambridge.]
FAM. 74. MORDELLIDAE (incl. RHIPIPHORIDAE).—_Head peculiarly formed, vertex lobed or ridged behind, so that in extension it reposes on the front edge of the pronotum; capable of great inflection and then covering the prosternum; hind coxae with laminae forming a sharp edge behind, frequently very large._ This family is a very distinct one, though it exhibits great variety. Lacordaire has pointed out that Rhipiphoridae cannot at present be satisfactorily distinguished from Mordellidae. Leconte and Horn separate the two by the fact that the sides of the prothorax form a sharp edge in Mordellidae, but not in Rhipiphoridae. A better character would perhaps be found by a study of the head, but as this would clearly result in a radical change in the composition of the two families it is preferable to treat them at present as only sub-families: if placed on a similar basis to the preceding families, the group would however form, not two, but several families. Besides the unusual shape of the head (Fig. 139, D) the ventral region of the body is remarkably formed, being very convex, and in many Mordellides terminating in a strong spinous process (Fig. 139, C). The elytra are, in several Rhipiphorids, of the groups Myoditini and Rhipidiini, reduced to a very small size, and the wings are not folded. The Mordellidae are remarkable for their activity; in the perfect state they usually frequent flowers, and fly and run with extreme rapidity. Mordellides are amongst the most numerous and abundant of the European Coleoptera, and in Britain the Anaspini swarm on the flowers of bushes and Umbelliferae. The {268}life-histories appear to be singularly varied; but unfortunately they are incompletely known. The larvae of some of the Mordellids have been found in the stems of plants, and derive their nutriment therefrom. This is said by Schwarz to be undoubtedly the case with _Mordellistena floridensis_. Coquillett has found the larvae of _M. pustulata_ in plant-stems under circumstances that render it highly probable that they were feeding on a Lepidopterous larva contained in the stems; and Osborn found a similar larva that was pretty certainly a _Mordellistena_, and fed voraciously on Dipterous larvae in the stems of a plant. The little that is known as to the metamorphoses of _Mordella_ and _Anaspis_ shows that they live in old wood, but does not make clear the nature of their food.
[Illustration: Fig. 139—_Mordellistena floridensis._ America. (After Riley.) A, Larva; B, pupa; C, imago; D, outline of detached head of imago of _M. pumila_, to show the neck.]
Although it has been ascertained that the Rhipiphorides exhibit instances of remarkable metamorphosis, their life-histories are still very imperfectly known. Dr. Chapman has ascertained some particulars as to _Metoecus paradoxus_, which has long been known to prey in the larval state on the larvae of the common social wasps.[137] The eggs are apparently not deposited in the nests of the wasps, but in old wood. The young larva is a triungulin, similar to that of the Cantharidae, we shall subsequently describe. It is not known how it makes its way to the wasps' nests, but it is possible that when a wasp visits some old wood haunted by these larvae, some of them may attach themselves to it and be carried to the wasps' nests. When {269}access is gained to the cells the little _Metoecus_ pierces the skin of one of the wasp-grubs, and entering in it feeds on the interior; after it has increased in size it emerges, changes its skin, and assumes a different form and habits; subsequently, as an external parasite, entirely devouring the wasp-larva, and then becoming a pupa, and finally a perfect _Metoecus_, in the cell of the wasp. The wasps, though they investigate the cells, do not apparently entertain any objection to the _Metoecus_, though there may be sometimes as many as twenty or thirty of the destroyers in a single nest. A few hours after the _Metoecus_ has become a winged Insect and has escaped from the cells, it appears however, from the observations of Erné[138] on nests of wasps in captivity, that the wasps become hostile to the foreigners, and it is probable that in a state of nature these leave the nest as quickly as possible. _Emenadia flabellata_, a genus allied to _Metoecus_, has been discovered by Chobaut to have a similar life-history, except that it attacks a solitary wasp of the genus _Odynerus_.[139] An old record to the effect that a second species of _Emenadia_, _E. bimaculata_, lives in the stalks of _Eryngium campestre_, on the pith, is now thought to be erroneous. Fabre has found the larvae and pupae of another Rhipiphorid in the cells of a bee, _Halictus sexcinctus_.
The most remarkable of the Rhipiphorids, from the point of view of its habits, is certainly _Symbius blattarum_, which is now treated as the same as an Insect previously described by Thunberg from specimens found in amber and called _Ripidius pectinicornis_. This species is parasitic in cockroaches; the male and female are very different, the former being an
## active winged Insect, while the female is worm-like, differing but little
from the larva, and never leaving the body of the cockroach. It is to be regretted that the life-history is not better known. The species has been found on board ship in vessels coming from India; the male has been met with in several European countries, but the female is excessively rare.
FAM. 75. CANTHARIDAE OR MELOIDAE (_Blister-beetles_, _Oil-beetles_).-_-Head with an abrupt neck; elytra and sides of the abdomen without any coadaptation; each claw of the feet with a long appendage closely applied beneath it._ This distinct family consists of Heteromera with soft integument, and is remarkable for the fact that many of its members contain a substance that when extracted {270}and applied to the human skin, possesses the power of raising blisters. The life-history is highly remarkable, the most complex forms of hyper-metamorphosis being exhibited. The species now known amount to about 1500; there can be no difficulty in recognising a member of the family by the above characters, except that in a very few cases each claw bears a projecting tooth, instead of an elongate appendage parallel with itself. The penultimate tarsal joint scarcely ever broader than the preceding; the colour and style of markings are extremely varied. There are two very distinct sub-families, Cantharides and Meloides; the former are winged Insects, and are frequently found on flowers or foliage. The Meloides are wingless, and consequently terrestrial; they have a very short metasternum, so that the middle coxae touch the hind; and they also have very peculiar wing-cases, one of the two overlapping the other at the base; in a few Meloids the wing-cases are merely rudiments.
The post-embryonic development of these Insects is amongst the most remarkable of modern entomological discoveries. The first steps were made by Newport in 1851,[140] and the subject has since been greatly advanced by Fabre, Riley, and others. As an example of these peculiar histories, we may cite Riley's account[141] of _Epicauta vittata_ (Fig. 140), a blister-beetle living at the expense of North American locusts of the genus _Caloptenus_. The locust lays its eggs underground, in masses surrounded by an irregular capsule, and the _Epicauta_ deposits its eggs in spots frequented by the locust, but not in special proximity to the eggs thereof. In a few days the eggs of the blister-beetle hatch, giving rise to little larvae of the kind called triungulin (Fig. 140, A), because each leg is terminated by three tarsal spines or claws. In warm, sunny weather these triungulins become very active; they run about on the surface of the ground exploring all its cracks, penetrating various spots and burrowing, till an egg-pod of the locust is met with; into this the triungulin at once eats its way, and commences to devour an egg. Should two or more triungulins enter the same egg-pod, battles occur till only one is left.
{271}[Illustration: FIG. 140.—Hypermetamorphosis of _Epicauta vittata_. North America. (After Riley.) A, Young larva or triungulin; B, Caraboid instar or second larva; C, coarctate larva, or instar between the Scarabaeoid and Scolytoid larva; D, Scarabaeoid larva, from which the Scolytoid, or sixth, instar differs but little; E, pupa; F, imago.]
After a few days passed in devouring a couple of eggs, the triungulin sheds its skin and appears as a different larva (Fig. 140, B), with soft skin, short legs, small eyes, and different form and proportions; a second moult takes place after about a week, but is not accompanied by any very great change of form, though the larva is now curved, less active, and in form like a larva of Scarabaeidae; when another moult occurs the fourth instar appears as a still more helpless form of larva (Fig. 140, D), which increases rapidly in size, and when full grown leaves the remains of the egg-pod it has been living on, and forms a small cavity near by; here it lies on one side motionless, but gradually contracting, till the skin separates and is pushed down to the end of the body, disclosing a completely helpless creature that has been variously called a semi-pupa, pseudo-pupa, or coarctate larva (Fig. 140, C); in this state the winter is passed. In spring the skin of the coarctate larva bursts, and there crawls out of it a sixth instar which resembles the fourth (Fig. 140, D), except in the somewhat reduced size and greater whiteness. It is worthy of remark that the skin it has deserted retains its original form almost intact. In this sixth instar the larva is rather active and burrows about, {272}but does not take food, and in the course of a few days again moults and discloses the true pupa (Fig. 140, E). As usual in Coleoptera this instar lasts but a short time, and in five or six days the perfect beetle appears (Fig. 140, F). It is extremely difficult to frame any explanation of this complex development; there are, it will be noticed, no less than five stages interposed between the first larval instar and the pupal instar, and the creature assumes in the penultimate one a quasi-pupal state, to again quit it for a return to a previous state. It is possible to look on the triungulin and the pupal instars as special adaptations to external conditions; but it is not possible to account for the intermediate instars in this way, and we must look on them as necessitated by the physiological processes going on internally. Nothing, however, is known as to these. It may be well to mention that, after describing and figuring (_loc. cit._) this series of instars, Riley changed his views as to their nomenclature.[142] The following summary of the metamorphosis, to which we have added the two nomenclatures of Riley—the original one, when different from the amended one, being given in square brackets—may therefore be useful, viz.—Egg; 1, triungulin-larva—moult; 2, Caraboid larva [second larva, Caraboid stage]—moult; 3, Scarabaeoid larva [second larva, Scarabaeoid stage]—moult; 4, Scarabaeoid larva [second larva, ultimate stage] (large amount of food and much growth)—moult; 5, coarctate larva [pseudo-pupa, or semipupa]; 6, Scolytoid larva [third larva] (active, but little or no food taken)—moult; 7, pupa—moult; 8, perfect Insect.
M. Fabre has succeeded in elucidating the history of _Sitaris humeralis_, a Cantharid that lives at the expense of bees of the genus _Anthophora_.[143] The eggs of the _Sitaris_ are deposited in the earth in close proximity to the entrances to the bees' nests, about August. They are very numerous, a single female producing, it is believed, upwards of 2000 eggs. In about a month—towards the end of September—they hatch, producing a tiny triungulin of black colour; the larvae do not, however, move away, but, without taking any food, hibernate in a heap, remaining in this state till the following April or May, when they become active. Although they are close to the abodes of the bees they do not enter them, but seek to attach themselves {273}to any hairy object that may come near them, and thus a certain number of them get on to the bodies of the _Anthophora_ and are carried to its nest. They attach themselves with equal readiness to any other hairy Insect, and it is probable that very large numbers perish in consequence of attaching themselves to the wrong Insects. The bee in question is a species that nests in the ground and forms cells, in each of which it places honey and lays an egg, finally closing the receptacle. It is worthy of remark that in the case of the _Anthophora_ observed by M. Fabre, the male appears about a month before the female, and it is probable that the vast majority of the predatory larvae attach themselves to the male, but afterwards seize a favourable opportunity, transfer themselves to the female, and so get carried to the cells of the bee. When she deposits an egg on the honey, the triungulin glides from the body of the bee on to the egg, and remains perched thereon as on a raft, floating on the honey, and is then shut in by the bee closing the cell. This remarkable act of slipping on to the egg cannot be actually witnessed, but the experiments and observations of the French naturalist leave little room for doubt as to the matter really happening in the way described. The egg of the bee forms the first nutriment of the tiny triungulin, which spends about eight days in consuming its contents; never quitting it, because contact with the surrounding honey is death to the little creature, which is entirely unfitted for living thereon. After this the triungulin undergoes a moult and appears as a very different creature, being now a sort of vesicle with the spiracles placed near the upper part; so that it is admirably fitted for floating on the honey (Vol. V. Fig. 86, 10). In about forty days, that is, towards the middle of July, the honey is consumed, and the vesicular larva after a few days of repose changes to a pseudo-pupa (11 of the fig. cited) within the larval skin. After remaining in this state for about a month, some of the specimens go through the subsequent changes, and appear as perfect Insects in August or September. The majority delay this subsequent metamorphosis till the following spring, wintering as pseudo-pupae and continuing the series of changes in June of the following year; at that time the pseudo-pupa returns to a larval form (12 of the fig. cited), differing comparatively little from the second instar. The skin, though detached, is again not shed, so that this ultimate larva is enclosed in two {274}dead skins; in this curious envelope it turns round, and in a couple of days, having thus reversed its position, becomes lethargic and changes to the true pupa, and in about a month subsequent to this appears as a perfect Insect, at about the same time of the year as it would have done had only one year, instead of two, been occupied by its metamorphosis. M. Fabre employs the term, third larva, for the instar designated by Riley Scolytoid larva, but this is clearly an inconvenient mode of naming the instar. _Sitaris humeralis_ is now very rare in Britain, but it seems formerly to have been more common, and it is not improbable that its triungulin may have been the "_Pediculus melittae_," that was believed by Kirby to be a sort of bee-louse. Some species of the genus _Meloe_ are still common in Britain, and the Insects may be seen with heavy distended abdomen grazing on herbage in the spring. The females are enormously prolific, a single one producing, it is believed, about 10,000 eggs. _Meloe_ is also dependent on _Anthophora_, and its life-history seems on the whole to be similar to that of _Sitaris_; the eggs are, however, not necessarily deposited in the neighbourhood of the bees' nests, and the triungulins distribute themselves on all sorts of unsuitable Insects, so that it is possible that not more than one in a thousand succeeds in getting access to the _Anthophora_ nest. It would be supposed that it would be a much better course for these bee-frequenting triungulins to act like those of _Epicauta_, and hunt for the prey they are to live on; but it must be remembered that they cannot live on honey; the one tiny egg is their object, and this apparently can only be reached by the method indicated by Fabre. The history of these Insects certainly forms a most remarkably instructive chapter in the department of animal instinct, and it is a matter for surprise that it should not yet have attracted the attention of comparative psychologists. The series of actions, to be performed once and once only in a lifetime by an uninstructed, inexperienced atom, is such that we should _a priori_ have denounced it as an impossible means of existence, were it not shown that it is constantly successful. It is no wonder that the female _Meloe_ produces 5000 times more eggs than are necessary to continue the species without diminution in the number of its individuals, for the first and most important act in the complex series of this life-history is accomplished by an extremely indiscriminating instinct; the {275}newly hatched _Meloe_ has to get on to the body of the female of one species of bee; but it has no discrimination whatever of the kind of object it requires, and as a matter of fact, passes with surprising rapidity on to any hairy object that touches it; hence an enormous majority of the young are wasted by getting on to all sorts of other Insects; these larvae have been found in numbers on hairy Coleoptera as well as on flies and bees of wrong kinds; the writer has ascertained by experiment that a camel's-hair brush is as eagerly seized, and passed on to, by the young _Meloe_ as a living Insect is.
The histories of several other Cantharids have been more or less completely discovered. Fabre has found the larva of _Cerocoma schaefferi_ attacking the stores of provisions laid up by a fossorial wasp of the genus _Tachytes_, and consisting of Orthoptera of the family Mantidae. The student who wishes for further information may refer to M. Beauregard's work on this family.[144]
Some half-dozen species of the genus _Cephaloon_ found in Siberia, Japan, and North America, have, by some authorities, been separated as the family Cephaloidae. Nothing is known as to the metamorphosis of these rare beetles; and at present it is not necessary to distinguish them from Cantharidæ.
FAM. 76. TRICTENOTOMIDAE.—_Large Heteromera, with powerful free projecting mandibles; the antennae long, but with the terminal three joints short, with angular projections on one side._ This family includes only two genera and seven or eight species. They are very remarkable Insects; _Autocrates aenea_ being three inches long. The family is of considerable interest, as it seems to have no affinity with any other Coleoptera. The appearance of the species somewhat reminds one of Lucanidae, or Prionides; but Trictenotomidae have even less relation to those beetles than they have to the members of the Heteromerous series. The Trictenotomidae appear to be found only in the primitive forests of the Indian and Indo-Malayan regions. Nothing is known as to their life-histories.
{276}SERIES V. PHYTOPHAGA.
_Tarsi apparently four-jointed, the three basal joints usually densely set with cushion-like pubescence beneath; the third joint different in form, being divided into two lobes, or grooved on its upper surface so as to allow of the fourth joint being inserted near its base instead of at its extremity. Head not forming a definite prolonged beak; its labrum visible, the palpi rarely (and even then not completely) occluded in the mouth._
This great series of beetles includes something like 35,000 species. It approaches, like all the other series, the Polymorpha, especially the family Erotylidae placed therein, but in the great majority of cases there is no difficulty in recognising its members. The tarsi have never the Heteromerous formula, the head is not constructed like that of Rhynchophora, nor the mouth and feet like those of Adephaga; the antennae are different from those of the Lamellicorns. The tarsi are really five-jointed, for careful inspection shows that the long claw-joint has at its extreme base a small nodule, which is undoubtedly the fourth joint (Fig. 142, B). In speaking of the joints it is, however, customary not to refer to this small and functionally useless joint at all, and to call the claw-joint the fourth; when the little joint is referred to it may be called the true fourth joint.
Nearly the whole of the enormous number of species of this series are directly dependent on the vegetable kingdom for their nutriment; they are therefore well styled Phytophaga. This term is, however, restricted by some systematists to the family we have called Chrysomelidae. Although there is enormous variety in this series, three families only can be at all naturally distinguished, and this with difficulty. Of these the Bruchidae are seed-feeders, the Chrysomelidae, as a rule, leaf-feeders, the Cerambycidae wood and stem-feeders. The number of exceptions to this rule is but small, though certain Cerambycidae and certain Chrysomelidae live on roots.
FAM. 77. BRUCHIDAE.—_Prosternum extremely short; in front perpendicular; behind the coxae, forming merely a transverse lamina with pointed extremity. Hind femora more or less {277}thickened._ This comparatively small family includes about 700 species of small, unattractive beetles. The larvae live in seeds; hence some of the species are liable to be transported by means of commerce; some of them do considerable injury; peas and beans being specially subject to their attacks. They are able to complete their growth with a very small amount of nutriment, some of them consuming only a portion a little larger than themselves of a bean or pea. The larvae are fat maggots without legs, but Riley has discovered that the young larvae of _Bruchus pisi_ and _B. fabae_ have, when first hatched, three pairs of legs which are subsequently lost. They also have peculiar spinous processes on the pronotum. Both of these characteristics may be correlative with the transient differences in the activities of the larva, for the little creature is not at first located in the pea, but mines a gallery in the pod, in which it moves about, subsequently entering the pea and losing its legs. There is a good deal of difference in these respects between the two species—_B. pisi_ and _B. fabae_—examined by Riley, and as but little is known of the life-histories of other Bruchidae it is probable that still greater variety prevails. Heeger has found that _Bruchus lentis_ sometimes requires two seeds to enable it to complete its growth; it is, notwithstanding its legless state when half-grown, able to migrate by dropping to the earth, and dragging itself along by its mandibles till it comes to another pod into which it bites its way.
[Illustration: Fig. 141—_Bruchus pisi_ or pea-weevil. A, Young larva; B, prothoracic spinous process; C, post-embryonic leg, greatly magnified; D, pea-pod, with tracks of entry; E, portion of pod, with egg, and the subsequently formed track, magnified; F, imago. (After Riley.)]
The family has, until recently, been placed in the {278}Rhynchophorous series, with which it has, however, no direct connection. On the other hand, it is so closely connected with Chrysomelidae that it is not possible to indicate good characters to distinguish the two at present. The Australian genus _Carpophagus_, and the large South American species of _Caryoborus_ appear to be quite indistinguishable as families, though Lacordaire and Chapuis placed one in Bruchidae, the other in Chrysomelidae. The definition we have given applies, therefore, to the majority of the family, but not to the aberrant forms just mentioned. The European genus _Urodon_ appears to belong to Anthribidae, not to Bruchidae. The family Bruchidae is called Mylabridae by some.
FAM. 78. CHRYSOMELIDAE.—_Antennae moderately long; eyes moderately large, usually not at all surrounding the insertion of the antennae; upper surface usually bare, frequently brightly coloured and shining._ This enormous family comprises about 18,000 species of beetles, in which the form and details of structure are very varied. No satisfactory character for distinguishing Chrysomelidae from Cerambycidae has yet been discovered, although the two families are certainly distinct and natural. Most of the Chrysomelidae live on foliage; few of them are more than half an inch long, whereas the Cerambycidae are wood-feeders and usually of more elongate form and larger size. The potato beetle, or Colorado beetle, that occasioned so much destruction in North America some thirty years ago, and the introduction of which into Europe was anticipated with much dread, is a good example of the Chrysomelidae. The turnip flea, a tiny hopping beetle, is among the smallest forms of the family, and is a member of another very extensive subdivision of Chrysomelidae, viz. Halticides. The term Phytophaga is by many naturalists limited to Chrysomelidae, the Cerambycidae being excluded. The classification of the family is but little advanced, but the enormous number of species of Chrysomelidae are placed in four divisions, viz.:—
[Illustration: Fig. 142—_Doryphora decemlineata_, the potato beetle. North America. A, Imago; B, hind-tarsus. 3, third joint; 4, true fourth joint; 5, so-called fourth joint.]
{279}Prothorax much narrower at the base than the elytra, and usually without side-margins (raised edges). Sub-fam. 1. Eupoda; with three divisions, Sagrides, Donaciides, Criocerides.
The basal ventral plates of the abdominal segments are somewhat shorter in the middle than at the sides, the fourth one being often invisible in the middle, while the fifth is very large. Sub-fam. 2. Camptosomes; with six divisions, Megascelides, Megalopides, Clythrides, Cryptocephalides, Chlamydes, Sphaerocarides.
In the other two groups there is no great disparity between the fourth and fifth ventral plates.
Prothorax not greatly narrower at the base than the elytra, and usually with distinct edges at the outsides. Sub-fam. 3. Cyclica; with four divisions, Lamprosomides, Eumolpides, Chrysomelides, Galerucides.
Front of the head bent downwards or inflexed, so that the mouth is on the lower aspect. Antennae inserted close together on the most anterior part of the head, so that they are more forward than the mouth. Sub-fam. 4. Cryptostomes; with two divisions Hispides, Cassidides.
In the other three divisions the mouth is placed as usual, but the insertion of the antennae varies a good deal.
The larvae of about 100 species of the family are known; they are arranged in accordance with their habits, by Chapuis,[145] in six groups, viz.:
1. Elongate larvae, living under water, and there undergoing their metamorphosis. (Donaciides.)
2. Larvae mining in leaves, and undergoing their metamorphosis in the leaf. (Hispides and some Halticides.)
3. Short convex larvae, frequently with leathery and pigmented integuments, living exposed on plants. (Most of the Cyclica.)
4. Larvae of short form; covering the body with excrementitious matter. (Some Criocerides.)
5. Peculiar larvae of short form, spiny, and protecting their bodies by excrementitious matter attached by a special apparatus, the excrement itself being modified so as to be suitable for retention. (Cassidides.)
6. Elongate, pallid, larvae with curved abdomen; living in shell-like cases, and undergoing metamorphosis therein. (Most of the Camptosomes, the habits of which are known.)
Though our knowledge of these larvae extends to only about 100 out of 18,000 species, the above category by no means includes all the kinds of larvae; Captain Xambeu having recently discovered that the larva of _Chrysochus pretiosus_ lives in the earth feeding on roots after the manner of a _Rhizotrogus_ larva, which it resembles. The larva of _Sagra splendida_ lives {280}inside the stems of _Dioscorea batatas_, in swellings; the group Sagrides, to which it belongs, is a very anomalous one.
i. Eupoda. The beetles of the genus _Donacia_ are of special interest. They form, with the genus _Haemonia_, a peculiar group, well represented in Europe, and also in our own country. They are all connected with aquatic plants, the species of _Haemonia_ living entirely under water, while the _Donacia_ live in the imago-state an aërial life, though many of them enter the water with great readiness, and, it is said, are able to take wing from the surface. The larvae live on the roots of aquatic plants, and derive not only nutriment but air therefrom; they pass several months as pupae (or as resting larvae waiting for pupation), under water in cocoons which they construct, and which, incredible as it may seem, are filled with air, not water. Exact details as to the construction of these cocoons are wanting. It was formerly absurdly supposed that the larva swelled itself out to the size of the cocoon it was about to make, and so served as a mould, subsequently contracting. The observations of Schmidt-Schwedt[146] make it, however, more probable that the plant itself furnishes the air which, under pressure of the water (so he supposes), fills the cocoon; the larva wounds the root, piercing to an air-vessel and then constructs the cocoon on this spot, leaving to the last moment an orifice, according to Schmidt, as an exit for the water. The larva uses a similar artifice for obtaining air; it has no gills, but is provided near the extremity of the body with two sharp chitinous processes which it drives into the root of the plant till it penetrates an air-vessel. Schmidt thinks the processes serve as conduits to conduct the air to the tracheae, but Dewitz thinks the air enters the larva in a more normal manner, by means of a stigma placed at the base of the piercing process. A similar larva exists in _Haemonia_; which genus is additionally interesting from the fact that the imago lives entirely submerged. It is not known how it breathes. This genus is the only member of the Chrysomelidae that does not possess the structure of the feet that is characteristic of the Phytophaga. The late Professor Babington about sixty years ago found _H. curtisi_ at Cley on the Norfolk coast on submerged _Potamogeton pectinatus_, but it has not been met with there for a great many years.
The larvae of Criocerides are of two kinds, in one of which the {281}body is peculiarly shaped in conformity with the curious habit of using the excrement as a covering. The larva is less elongate than usual, and has the anus placed on the upper surface, and formed so that the excrement when voided is pushed forward on to the Insect; here it is retained by means of a slimy matter, and a thick coat entirely covering the creature, is ultimately formed. The larva of _Lema melanopa_ is not uncommon about Cambridge, where it feeds on the leaves of growing corn. It is a remarkable fact that even in one genus the species have some of them this habit, but others not. The species of _Crioceris_ living on lilies—_C. merdigera_, _e.g._—are noted for possessing it; while _C. asparagi_ does not protect itself in this way, but emits fluid from its mouth when disturbed. This larva is a serious nuisance in some localities to the cultivators of asparagus. The eggs are deposited on the stems of the plant—as shown in our figure—sometimes in great numbers.
The perfect Insects of many of the Criocerides possess a stridulating organ. Two contiguous areas at the base of the last dorsal segment, where they can be rubbed by the tips of the elytra, are slightly elevated and bear very close and fine straight lines.
[Illustration: Fig. 143—_Crioceris asparagi._ A, Eggs in position on stem of asparagus; B, one egg much enlarged; C, young larva. Cambridge.]
ii. The Camptosomes, as we have already noticed, are distinguished by a peculiar structure of the abdomen. This character appears to be connected with a very remarkable habit, viz. the formation of a case to envelop the egg. The tip of the abdomen is somewhat curved downwards, and, in the female, bears a hollow near the extremity; when an egg is extruded the female holds it in this hollow by means of the hind legs, and envelops it with a covering said to be excrementitious. When the larva hatches, it remains within this case, and {282}subsequently enlarges it by additions from its own body. The beautiful Insects of the genus _Cryptocephalus_, which is fairly well represented in Britain, belong to this division. The exotic group Megalopodes is incorrectly placed in Camptosomes; the side pieces of the prothorax meet in it behind the middle coxae, as they do in Rhynchophora. The species of Megalopodes stridulate by means of an area on the base of the meso-scutellum rubbed by a ridge inside the pronotum, as in the Cerambycidæ.
iii. The division Cyclica includes the great majority of Chryomelidae; we have not less than 170 species in Britain. The larvae live, like those of Lepidoptera, at the expense of foliage, and the species frequently multiply to such an extent as to be injurious. Some of them are destroyed in great numbers by Hymenopterous parasites, the Braconid genus _Perilitus_ being one of the best known of these; in some cases the parasite deposits its eggs in either the larva or perfect Insect of the beetle, and the metamorphoses of the parasites in the latter case are sometimes, if not usually, completed, the larvae emerging from the living beetles for pupation.
iv. The Cryptostomes, though comparatively few in number of species, include some very remarkable beetles. There are two groups, Hispides and Cassidides. The former are almost peculiar to the tropics and are not represented by any species in the British fauna. The head in this group is not concealed; but in the Cassidides the margins of the upper surface are more or less expanded, so that the head is usually completely hidden by the expansion of the pronotum. Both the groups are characterised by the antennae being inserted very near together, and by the short claw-joint of the feet. _Hispa_ is one of the most extensive of the numerous genera of Hispides, and is remarkable from the imago being covered on the surface with long, sharp spines. But little is known as to the metamorphosis, beyond the fact already alluded to, that the larvae of several species mine the interior of leaves. The larva of _Hispa testacea_, according to Perris,[147] makes use of the leaves of _Cistus salvifolius_ in Southern Europe; it is broad and flat, and possessed of six short legs. The eggs are not deposited by the parents inside the leaves, but are probably attached to various parts of the plant. After hatching, the young larva enters a leaf, and feeds on the parenchyma without rupturing {283}the epidermis; but when it has consumed about three-fourths of the soft interior of the leaf it ruptures the epidermis of the upper surface, and seeks another leaf; this found, it places itself on the midrib, tears the upper epidermis, and lodges itself in the leaf. In the case of this second leaf it attacks the parenchyma in the neighbourhood of the petiole, and so forms an irregular tube which has an open mouth, the point of entry. In this tube it undergoes its metamorphosis. Each larva, it is said, always makes use of two leaves, and of two opposed leaves. A knowledge of the habits of some of the larger of the exotic Hispides would be of much interest.
[Illustration: Fig. 144—Pupa of Cassidid beetle (? _Aspidomorpha_ sp.). A, With appendage extended; B, with the appendage reposing on the back. New Britain.]
The Cassidides, in addition to the curious marginal expansion of their upper surface, have the power of withdrawing the head into the thorax, and hence they are often called shield or tortoise-beetles. They exhibit considerable variety in form and colour, and some of them display a peculiar metallic reflection of great delicacy and beauty; this disappears entirely after death, but it may be restored by thoroughly moistening the dead Insect. The colour, therefore, probably depends on the presence of water in the integument. The larvae of Cassidides are notorious on account of their habit of covering their bodies with dried excrement, for which purpose they are provided with a forked {284}process at the posterior extremity; this serves to place the protecting matter in a proper position and to retain it there. The excrement assumes in various species forms so peculiar that they cannot be considered merely incidental. In several species this covering-matter is like lichen. This is the case with _Dolichotoma palmarum_, the larva of which has, in place of the usual fork, a more complex appendage on the back for the purpose of preparing and retaining its peculiar costume. The pupae, too, sometimes retain the larval skin. An extremely remarkable pupa of a Cassidid—possibly of the genus _Aspidomorpha_—was recently found by Dr. Arthur Willey in New Britain (Fig. 144). The back of the pupa is covered with a complex appendage, so that the creature has no resemblance to an Insect; this appendage is perhaps capable of being moved, or even extended (Fig. 144, A), during life. Whether it may be formed by the retention of portions of the moulted skins of the larva we cannot say with certainty.
[Illustration: Fig. 145—Nest of intestinally-made filaments under which the larva of _Porphyraspis tristis_ lives.]
The most remarkable of the Cassidid coverings yet discovered are those formed by certain small beetles of the tropical American genus _Porphyraspis_. _P. tristis_ is apparently a common Insect at Bahia, where it lives on a cocoa-palm. The larva is short and broad, and completely covers itself with a very dense coat of fibres, each many times the length of the body, and elaborately curved so as to form a round nest under which the larva lives. On examination it is found that these long threads are all attached to the anal extremity of the Insect, and there seems no alternative to believing that each thread is formed by small pieces of fibre that have passed through the alimentary canal, and are subsequently stuck together, end to end. The process of forming these long fibres, each one from scores of pieces of excrement, and giving them the appropriate curve, is truly remarkable. The fibres nearest to the body of the larva are abruptly curled so as to fit exactly, and make an even surface; but the outside fibres stand out in a somewhat bushy fashion. The construction is much like that of a tiny bird's nest. Señor Lacerda informed the writer that the larva makes a nest as soon as it is hatched. Another _Porphyraspis_—_P. palmarum_—has been recorded as {285}forming similar nests on a species of _Thrinax_ in St. Domingo. Candèze says[148] that when it has completed its growth the larva ejects on to the leaf a quantity of semi-liquid matter, and this, on drying, sticks the nest to the leaf, so that the metamorphosis is effected under shelter.
FAM. 79. CERAMBYCIDAE (_Longicorns_).—_Form usually oblong, not much curved in outline at the sides; surface very frequently rendered dull by a very minute hairiness, which often forms a pattern; antennae usually long, and their insertion much embraced by the eyes._ This great family of beetles includes some 12,000 or 13,000 known species. The elegance and variety of their forms and the charm of their colours have caused them to attract much attention, so that it is probable that a larger proportion of the existing species have been obtained than is the case in any other of the great families of Coleoptera. Still it is not likely that one-half of the living forms are known. It is not possible at present to point out any one character of importance to distinguish Cerambycidae from Chrysomelidae, though the members of the two families have, as a rule, but little resemblance in external appearance. Most of them live on, or in, wood, though many are nourished in the stems of herbaceous plants. The larvae live a life of concealment, and are soft, whitish grubs with powerful mandibles, and usually with a comparatively small head, which is not much exserted from the thorax. Most of them are without legs, but a good many have three pairs of small legs, and there are numerous cases in which the surface of the body is furnished above or below with swellings believed to act as pseudopods (Fig. 84), and help the larvae to move about in their galleries; but this is probably not the sole function of these organs, as their surface is varied in character, and often not of a kind that appears specially adapted to assist in locomotion. There is a slight general resemblance between the larvae of Cerambycidae and those of Buprestidae, and when the thorax of a Longicorn larva is unusually broad, _e.g._ _Astynomus_, this similarity is very pronounced.
[Illustration: Fig. 146—_Saperda populnea._ Britain.]
{286}The modes of life of Cerambycid larvae exhibit considerable variety, and much perfection of instinct is displayed by the larvae, as well as by the mother beetles. The larvae of _Saperda populnea_, are common in certain woods in the South of England in the stems of aspen; they consume only a small quantity of the interior of the stem, and are probably nourished by an afflux of sap to the spot where they are situated. _Elaphidion villosum_ is called the oak-pruner in North America. The parent beetle lays an egg near the axilla of a leaf-stalk or small stem, and the young larva enters this and feeds on the tender material; as it grows it enters a larger limb, and makes an incision within this in such a manner that the wood falls to the ground with the larva within it, the dead wood serving subsequently as pabulum and as a shelter, within which the metamorphosis is completed. The species of the American genus _Oncideres_ are called girdlers, because the parent beetle, after laying an egg in a small branch, girdles this round with a deep incision, so that the portion containing the larva sooner or later falls to the ground. The growth of a Longicorn larva frequently takes more than a year, and under certain circumstances it may be enormously prolonged. _Monohammus confusus_ has been known to issue from wooden furniture in a dwelling-house when the furniture was fifteen years old. Individuals of another Longicorn have issued from the wood of a table, twenty and even twenty-eight years after the felling of the tree from which the furniture was made. Sereno Watson has related a case from which it appears probable that the life of a Longicorn beetle extended over at least forty-five years.[149] It is generally assumed that the prolongation of life in these cases is due to the beetle resting quiescent for long after it has completed the metamorphosis. Recent knowledge, however, renders it more probable that it is the larval life that is prolonged; the larva continuing to feed, but gaining little or no nutriment from the dry wood in these unnatural conditions. Mr. C. O. Waterhouse had for some years a Longicorn larva under observation, feeding in this way in the wood of a boot-tree;[150] the burrows in the wood contained a great deal of minute dust indicating that the larva passed much matter through the alimentary canal, probably with little result in the way of nutriment.
{287}There are numerous Longicorns that bear a great resemblance in form and colour to Insects to which they are not related. Haensch[151] has noticed that species of the genus _Odontocera_ resemble various Hymenoptera, one species being called _O. braconoides_; he also observed that these Hymenoptera-like Longicorns, instead of withdrawing their underwings under the elytra as beetles generally do, vibrate them rapidly like Hymenoptera. A large number of Longicorns stridulate loudly by rubbing a ridge inside the pronotum on a highly specialised, striate surface at the base of the scutellum, and therefore covered up when the Insect is contracted in repose. A few produce noise by rubbing the hind femora against the edges of the elytra, somewhat after the fashion of grasshoppers. In this case there appears to be comparatively little speciality of structure, the femora bearing, however, more or less distinct small granules. The species of the Hawaiian genus _Plagithmysus_ produce sound in both these manners, the thoracic stridulating organ being beautifully developed, while in some species the margin of the elytra and base of the femora are also well adapted for the purpose of sound-production, and in a few species of the genus there are also highly-developed stridulating surfaces on the hind and middle coxae. This is the only case in which a beetle is known to possess more than one set of sound-organs in the imago state.
Three divisions of this family are distinguished, viz.—
1. Front coxae large and transverse; prothorax with distinct side margins. Sub-fam. 1. Prionides.
2. Front coxae not greatly extended transversely, thorax not margined; last joint of maxillary palpus not pointed, usually broader (more or less) than the preceding joint. Sub-fam. 2. Cerambycides.
3. Front coxae usually round and deeply embedded; last joint of maxillary palpus pointed; front tibiae with a more or less distinct, slanting groove on the inner side. Sub-fam. 3. Lamiides.
The Prionides are on the average considerably larger in size than the members of the other divisions, and they include some of the largest of Insects. The Amazonian _Titanus giganteus_ and the Fijian _Macrotoma heros_ are amongst the most gigantic. Some of the Prionides have a great development of the mandibles in the male sex analogous to that we have already noticed in Lucanidae. The larvae of the large Prionides appear in various parts of the world to have been a favourite food with native {288}tribes, and Lumholz states that they are really good eating. In consequence of the destruction of forests that has progressed so largely of late years these gigantic Prionides have become much rarer.
Several aberrant forms are included in Prionides. The genus _Parandra_ has five-jointed tarsi; the third joint being much smaller than usual, so that the fourth joint is not concealed by it. The Brazilian _Hypocephalus armatus_ was for long a subject of dispute as to its natural position, and was placed by different authorities in widely-separated families of Coleoptera. The structure of this aberrant Longicorn seems to be only explicable on the hypothesis of warfare amongst the males.[152] Nothing is, however, known as to the habits and history of the Insect, and only one or two specimens of the female have yet been obtained.
The family Spondylidae has been proposed for some of these aberrant Longicorns, but as it includes but very few, and highly discrepant, species, it is neither natural nor of much use for systematic purposes.
The Lamiides are the most highly specialised division of the Longicorns, and includes the larger number of the species. The front of the head is usually placed at right angles to the vertex, and in some cases (groups Hippopsini, Spalacopsini) it is strongly inflexed, so that the mouth is placed on the under side of the head. The extension of the eyes round the antennae is accompanied by very curious shapes of those organs, and not infrequently each eye is divided into two more or less widely-separated parts, so that the Insect has, on the external surface, four eyes.
SERIES VI. RHYNCHOPHORA.
_Head more or less prolonged in front to form a snout or beak, called rostrum. Tarsi four-jointed, usually at least the third joint broad and densely pubescent beneath._
This enormous series includes about 25,000 species, and as may well be imagined shows a great variety of structure amongst its forms. The vast majority may, however, be readily recognised by the two characters mentioned above. There are some cases in which the beak is indistinct, and others in which the tarsi are {289}five-jointed (_Dryophthorus_), and even slender (Platypides). In these cases a close examination shows that the gular region on the middle of the back of the under surface of the head cannot be detected, and that the back of the prosternum is very strongly consolidated by the side-pieces of the thorax meeting together and being very firmly joined behind the coxae. The beak is in the great majority perfectly distinct, though it varies so extremely in form that it can only be briefly described by saying that it is a prolongation of the head in front of the eyes, or that the antennae are inserted on its sides near to, or far from, the tip. It has been ascertained in many cases that the rostrum is used by the female to assist in placing the eggs in suitable places, a hole being bored with it; in some cases it is also used to push the egg far into the hole in which it has previously been placed by the ovipositor; but there are many forms in which it is fairly certain that it is not so used. What purpose it serves in the male is totally unknown. In many members of the series, the rostrum differs in form in the two sexes, and in most, if not in all, these cases it is clear that the distinctions tend in the direction of making the beak of the female more efficient for the mechanical purpose we have mentioned.
[Illustration: Fig. 147.—_Eugnoristus monachus_ ♀. Madagascar. A, The imago; B, front of pronotum, head, and rostrum.]
It was proposed by Leconte and Horn to separate this series from all the other Coleoptera as a primary division, and they looked on it as of lower or more imperfect structure. Packard has very properly protested against this interpretation; and there seems to be no reason whatever for considering the Rhynchophora as "lower" than other beetles; indeed we should be inclined to place such forms as Calandrides {290}amongst the most perfect of Insects; their external structure (as shown by _Eugnoristus monachus_, Fig. 147) being truly admirable.
Only four families of Rhynchophora can be at present accepted as satisfactory; one of these—Curculionidae—includes an enormous majority of the whole series. Though it is probable that it will ultimately be divided into several families, the attempts to that end that have already been made are not satisfactory.
FAM. 80. ANTHRIBIDAE.—_Palpi usually not covered, but distinct and flexible. Antennae often long, not elbowed, the first joint not very long. Third joint of tarsus small, usually much concealed by being embraced by the second joint. Pygidium exposed; propygidium deeply grooved in the middle._ This family includes 800 or more species, which are mostly tropical; it is very sparsely represented in the faunas of Europe and North America. It is quite distinct from Curculionidae with which it was formerly associated. It contains many graceful Insects having a certain resemblance with Longicorns on account of the large development of the antennae. The habits and metamorphoses are but little known. It seems probable that many species find their nutriment in old wood or boleti The larvae of some genera (_Cratoparis_ and _Araeocerus_) have legs, but in others the legs are wanting, and the larvae are said to completely resemble those of Curculionidae. In the larva of our tiny British species, _Choragus sheppardi_, the legs are replaced by three pairs of thoracic, sac-like pseudopods. This Insect makes burrows in dead branches of hawthorn. The larvae of the genus _Brachytarsus_ have been ascertained to prey on Coccidae.
[Illustration: Fig. 148—_Platyrhinus latirostris_, Anthribidae. Britain. A, the perfect Insect; B, tarsus and tip of tibia.]
FAM. 81. CURCULIONIDAE (Weevils).—_The beak of very variable length and thickness; the palpi small, nearly always concealed within the mouth, short, and rigid. Labrum absent. Antennae of the majority elbowed,_ i.e. _with the basal joint longer, and so formed that when it is laterally extended the other joints can be placed in a forward direction._ This enormous family includes {291}about 20,000 known species, and yet a large portion of the species yearly brought from the tropics still prove to be new. The rostrum or beak exhibits excessive variety in form, and is in many cases different in the sexes; in this case it is usually longer and thinner in the female. As the rostrum is one of the chief characters by which a member of the family may be recognised, it is necessary to inform the student that in certain forms (the Australian Amycterides, _e.g._) the organ in question may be so short and thick that it is almost absent. In these cases the Insect may be identified as a Curculionid by the gular area being absent on the under side of the head, and by the concealment of the palpi. The tarsi are usually of the same nature as those of Phytophaga, already described, but the true fourth joint is less visible. In the Brachycerides this joint is not present, and the third joint is not lobed. The palpi are flexible and more or less exserted in a very few species (Rhynchitides); in Rhinomacerides there is also present a minute labrum. The front coxae are deeply embedded, and in many forms the prosternum is peculiar in structure; the side-pieces (epimera) meeting at the back of the prosternum in the middle line. This, however, is not universal in the family, and it occurs in some other beetles (_e.g._, Megalopodides of the Phytophaga). The larvae are without legs. They are vegetarian, the eggs being deposited by the mother-beetle in the midst of the food. These larvae may be distinguished from those of Longicorns by the general form, which is sub-cylindric or rather convex, not flattened, and more particularly by the free, exserted head, the mouth being directed downwards; the attitude is generally a curve, and the anterior part of the body is a little the thicker. No part of plants is exempt from the attacks of the larvae of Curculionidae; buds, twigs, leaves, flowers, fruits, bark, pith, roots and galls may each be the special food of some Curculionid. Certain species of the sub-families Rhynchitides and Attelabides prepare leaves in an elaborate manner to serve as food and dwelling for their young. If young birches, or birch bushes from 5 to 10 feet in height, be looked at in the summer, one may often notice that some of the leaves are rolled so as to form, each one, a little funnel. This is the work of _Rhynchites_ (or _Deporaus_) _betulae_, a little Curculionid beetle (Fig. 149). An inspection of one of these funnels will show that it is very skilfully constructed.
{292}[Illustration: Fig. 149.—The leaf-rolling of _Rhynchites betulae_. Britain. A, Female beetle, magnified; B, the beetle forming the first incision on a leaf; C, the completed roll. (B and C after Debey.)]
The whole of a leaf is not used in the formation of a funnel, cuts being made across the leaf in suitable directions. The beetle standing on a leaf, as shown in the figure, proceeds to cut with its mandibles an incision shaped like an erect S, commencing at a certain part of the circumference, and ending at the midrib of the leaf; the beetle then goes to the other side of the midrib, and continues its incision so as to form another S-like curve considerably different from the first; being prostrate and less abrupt. Thus the blade of the leaf is divided into two halves by certain curved incisions, the midrib remaining intact. The little funnel-twister now commences to roll up the leaf to form the funnel; and this part of the work is greatly facilitated by the shape of the incisions. Going back to the spot where it commenced work, by the aid of its legs it rolls one side of the leaf round an ideal axis, somewhat on the same plan as that adopted by a grocer in forming a paper-funnel for sugar. The incisions are found to be just of the right shape to make the overlaps in the rolling, and to retain them rolled-up with the least tendency to spring back. After some other operations destined to facilitate subsequent parts of its task, the beetle enters the rolled-up part of the leaf and brings it more perfectly together; it again comes out and, pursuing a different system, holds on with the legs of one side of the body {293}to the roll, and with the other legs drags to it the portion of the leaf on the other side of the midrib so as to wrap this part (_i.e._ the result of its second incision) round the part of the funnel already constructed. This being done the Insect again enters the funnel, bites three or four small cavities on the inside of the leafy wall and deposits an egg in each. Afterwards it emerges and fits the overlaps together in a more perfect manner so as to somewhat contract the funnel and make it firmer; then proceeding to the tip, this is operated on by another series of engineering processes and made to close the orifice; this part of the operation being analogous to the closing by the grocer of his paper-funnel after the sugar has been put in. The operation of the beetle is, however, much more complex, for it actually makes a sort of second small funnel of the tip of the leaf, bends this in, and retains it by tucking in some little projections. The work, which has probably lasted about an hour, being now completed, the creature takes a longer or shorter rest before commencing another funnel. We have given only a sketch of the chief points of the work, omitting reference to smaller artifices of the craft master; but we may remark that the curved incisions made by the beetle have been examined by mathematicians and duly extolled as being conducted on highly satisfactory mathematical principles. It is impossible at present for us to form any conception as to the beetle's conceptions in carrying out this complex set of operations. Our perplexity is increased if we recollect its life-history, for we then see that neither precept or example can have initiated its proceedings, and that imitation is out of the question. The eggs hatch in their dark place, giving rise to an eyeless maggot, which ultimately leaves the funnel for the earth. The parts of this maggot subsequently undergo complete change to produce the motionless pupa of entirely different form, from which emerges the perfect Insect. Hence the beetle cannot be considered to have ever seen a funnel, and certainly has never witnessed the construction of one, though, when disclosed, it almost immediately sets to work to make funnels on the complex and perfect system we have so imperfectly described. More general considerations only add to the perplexity we must feel when reflecting on this subject. Why does the Insect construct the funnel at all? As a matter of protection it appears to be of little use, for the larvae are known to suffer from the attacks {294}of parasites as other Insects do. We have not the least reason for supposing that this mode of life for a larva is, so far as utility is concerned, better than a more simple and usual one. Indeed, extraordinary as this may appear, it is well known that other species of the same genus adopt a simple mode of life, laying their eggs in young fruits or buds. We think it possible, however, that a knowledge of the mode of feeding of this larva may show that a more perfect nutrition is obtained from a well-constructed cylinder, and if so this would to a slight extent satisfy our longing for explanation, though throwing no light whatever on the physiology or psychology of the artificer, and leaving us hopelessly perplexed as to why a beetle in ages long gone by should or could adopt a mode of life that by long processes of evolution should, after enormous difficulties have been overcome, attain the perfection we admire.[153]
FAM. 82. SCOLYTIDAE.—_Rostrum extremely short, broad; tibiae frequently denticulate externally; antennae short, with a broad club._ This family is not at all sharply distinguished from certain groups of Curculionidae (from Cossonides _e.g._), but as the species have somewhat different habits, and in the majority of cases can be readily distinguished, it is an advantage to separate the two families. About 1400 species are at present known. Most of them are wood- and bark-feeders; some bore into hard wood; a few mine in twigs or small branches of trees, but the majority live in the inner layers of the bark; and this also serves as the nidus of the larvae. A small number of species have been found to inhabit the stems of herbaceous plants, or to live in dry fruits. Owing to their retiring habits they are rarely seen except by those who seek them in their abodes, when they may often be found in great profusion. The mother-beetle bores into the suitable layer of the bark, forming a sort of tunnel and depositing eggs therein. The young larvae start each one a tunnel of its own, diverging from the parent tunnel; hence each batch of larvae produces a system of tunnels, starting from the parents' burrow, and in many species these burrows are {295}characteristic in form and direction, so that the work of
## particular Scolytids can be recognised by the initiated.
The Platypides bore into the wood of trees and stumps; they are chiefly exotic, and little is known about them. They are the most aberrant of all Rhynchophora, the head being remarkably short, flat in front, with the mouth placed on the under surface of the head, there being no trace of a rostrum: the tarsi are elongate and slender, the third joint not being at all lobed, while the true fourth joint is visible. Hence they have not the appearance of Rhynchophora. Some authorities treat the Platypides as a distinct family.
Some of the members of the group Tomicides also bore into the wood. Recent observations have shown that there is an important feature in the economy of certain of these wood-borers, inasmuch as they live gregariously in the burrow, and feed on peculiar fungi that develop there, and are called ambrosia. According to Hubbard[154], some species cultivate these fungi, making elaborate preparations to start their growth. The fungi, however, sometimes increase to such an extent as to seal up the burrows, and kill the Insects by suffocation.
Scolytidae sometimes multiply to an enormous extent, attacking and destroying the trees in wooded regions. Much discussion has taken place as to whether or not they are really injurious. It is contended by one set of
## partisans that they attack only timber that is in an unhealthy, dying, or
dead condition. It may be admitted that this is usually the case; yet when they occur in enormous numbers they may attack timber that is in a sort of neutral state of health, and so diminish its vigour, and finally cause its destruction. Hence it is of great importance that they should be watched by competent foresters.
The larvae of Scolytidae are said to completely resemble those of Curculionidae: except in the group Platypides, where the body is straight and almost cylindrical, and terminates in an oblique truncation bearing a short hard spine.[155]
FAM. 83. BRENTHIDAE.—_Form elongate; rostrum straight, directly continuing the long axis of the body, often so thick as to form an elongate head; antennae not elbowed._ The Brenthidae form a family of about 800 species, remarkable for the excessive {296}length and slenderness of some of its forms, and for the extreme difference in the sexes that frequently exists. It is well represented in the tropics only, and very little is known as to the natural history and development. These beetles are stated to be wood-feeders, and no doubt this is correct in the case of the majority of the species; but Mr. Lewis observed in Japan that _Zemioses celtis_ and _Cyphagogus segnipes_ are predaceous, and enter the burrows of wood-boring Insects to search for larvae as prey: they are very much modified in structure to permit this; and as the other members of the group Taphroderides are similar in structure, it is probable that they are all predaceous. Nothing whatever is known as to the larval history of these carnivorous forms. Indeed an uncertainty, almost complete, prevails as to the early stages of this family. Riley has given a sketch of a larva which he had no doubt was that of _Eupsalis minuta_, the North American representative of the family; if he is correct the larva differs from those of Curculionidae by its elongate form, and by the possession of thoracic legs: these, though small, are three-jointed. Descriptions, supposed to be those of Brenthid larvae, were formerly published by Harris and Motschoulsky; but it is now clear that both were mistaken.
[Illustration: Fig. 150—_Eupsalis minuta_. North America. A, Larva; B, pupa; C, female imago; D, head of male. (After Riley.)]
In the higher forms of Brenthidae the rostrum of the female is perfectly cylindrical and polished, and the mandibles are minute, hard, pointed processes placed at its tip. This organ is admirably adapted to its purpose; it being used for boring a hole in wood or bark, in which an egg is subsequently deposited. The males in these cases are extremely different, so that considerable curiosity is felt as to why this should be so. In some cases their head is thick, and there may be no rostrum, while large powerful mandibles are present.
In other cases the rostrum is slender, but of enormous length, so that it may surpass in this respect the rest of {297}the body, although this itself is so drawn out as to be quite exceptional in the Insect world:[156] the antennae are inserted near the tip of the rostrum instead of near its base, as they are in the female. The size of the males is in these cases usually much larger than that of the female.[157] The males of some species fight; they do not, however, wound their opponent, but merely frighten him away. In _Eupsalis_ it appears that the rostrum of the female is apt to become fixed in the wood during her boring operations; and the male then extricates her by pressing his heavy prosternum against the tip of her abdomen; the stout forelegs of the female serve as a fulcrum and her long body as a lever, so that the effort of the male, exerted at one extremity of the body of the female, produces the required result at the other end of her body. The New Zealand Brenthid, _Lasiorhynchus barbicornis_, exhibits sexual disparity in an extreme degree: the length of the male is usually nearly twice that of the female, and his rostrum is enormous. It is at present impossible to assign any reason for this; observations made at the request of the writer by Mr. Helms some years ago, elicited the information that the female is indefatigable in her boring efforts, and that the huge male stands near by as a witness, apparently of the most apathetic kind.
COLEOPTERA OF UNCERTAIN POSITION.
There are three small groups that it is impossible at present to place in any of the great series of beetles.
FAM. 84. AGLYCYDERIDAE.—_Tarsi three-jointed, the second joint lobed; head not prolonged to form a beak._ The two most important features of Rhynchophora are absent in these Insects, while the other structural characters are very imperfectly known, many parts of the external skeleton being so completely fused that the details of structure are difficult of appreciation. Westwood considered the tarsi to be really four-jointed, but it is not {298}at all clear that the minute knot he considered the third joint is more than the articulation of the elongate terminal joint. The family consists only of two or three species of _Aglycyderes_, one of which occurs in the Canary Islands, and one or two in New Zealand and New Caledonia. The former is believed to live in the stems of _Euphorbia canariensis_; a New Zealand species has been found in connection with the tree-ferna. _Cyathea dealbata_
[Illustration: Fig. 151—_Aglycyderes setifer_. Canary Islands. A, Imago; B, tarsus according to Westwood; C, according to nature; D, maxilla; E, labium.]
FAM. 85. PROTERHINIDAE.—_Tarsi three-jointed, the second joint lobed; head of the male scarcely prolonged, but that of the female forming a definite rostrum; maxillae and ligula entirely covered by the mentum._ As in the preceding family the sutures on the under side of the head and prosternum cannot be detected. The minute palpi are entirely enclosed in the buccal cavity. There is a very minute true third joint of the tarsus, at the base of the terminal joint, concealed between the lobes of the second joint. The family consists of the genus _Proterhinus_; it is confined to the Hawaiian Islands, where these Insects live on dead wood in the native forests. The genus is numerous in species and individuals.
[Illustration: Fig. 152—_Proterhinus lecontei_. Hawaiian Islands. A, Male; B, female; C, front foot, more magnified.]
STREPSIPTERA (or RHIPIPTERA, Stylopidae).—_Male small or minute; prothorax extremely small; mesothorax moderate, the elytra reduced to small, free slips; metathorax and wings very large; nervuration of the latter radiating, without cross nervules. Female a mere sac, with one extremity smaller and forming a sort of neck or head._
{299}[Illustration: Fig. 153.—Sexes of Strepsiptera. A, Male of _Stylops dalii_ (after Curtis); B, female of _Xenos rossii_ (after von Siebold).]
These curious Insects are parasitic in the interior of other Insects, of the Orders Hymenoptera and Hemiptera. Their structure and their life-histories entitle them to be ranked as the most abnormal of all Insects, and entomologists are not agreed as to whether they are aberrant Coleoptera or a distinct Order. The newly-hatched larva is a minute triungulin (Fig. 154), somewhat like that of _Meloe_; it fixes itself to the skin of the larva of a Hymenopterous Insect, penetrates into the interior, and there undergoes its metamorphoses, the male emerging to enjoy a brief period of an abnormally active, indeed agitated, existence, while the female never moves. It is important to note that these Strepsiptera do not, like most other internal parasites, produce the death of their hosts; these complete their metamorphosis, and the development of the parasite goes on simultaneously with that of the host, so that the imago of the Strepsipteron is found only in the imago of the host.[158] After the young _Stylops_ has entered its host it feeds for a week or so on the fat-body (apparently by a process of suction), then moults and assumes the condition of a footless maggot, in which state it remains till growth is completed. At the latter part of this period the history diverges according to sex; the female undergoes only a slight metamorphic development of certain parts, accompanied apparently by actual degradation of other parts; while the male goes on to pupation, as is normal in Insects. (We may remark that the great features of the development of the sexes are parallel with those of Coccidae in Hemiptera.) When the Hymenopterous larva changes to a pupa, the larva of the Strepsipteron pushes one extremity of its body between two of the abdominal rings of its host, so that this extremity becomes external, and in this position it completes its metamorphosis, the {300}male emerging very soon after the host has become an active winged Insect, while the female undergoes no further change of position, but becomes a sac, in the interior of which young develop in enormous numbers, finally emerging from the mother-sac in the form of the little triungulins we have already mentioned. This is all that can be given at present as a general account; many points of the natural history are still obscure, others have been merely guessed; while some appear to differ greatly in the different forms. A few brief remarks as to these points must suffice.
Bees carrying, or that have carried, Strepsiptera, are said to be stylopised (it being a species of the genus _Stylops_ that chiefly infests bees); the term is also used with a wider application, all Insects that carry a Strepsipterous parasite being termed stylopised, though it may be a Strepsipteron of a genus very different from _Stylops_ that attacks them. The development of one or more Strepsiptera in an Insect usually causes some deformity in the abdomen of its host, and effects considerable changes in the condition of its internal organs, and also in some of the external characters. Great difference of opinion prevails as to what these changes are; it is clear, however, that they vary much according to the species, and also according to the extent of the stylopisation. Usually only one _Stylops_ is developed in a bee; but two, three, and even four have been observed:[159] and in the case of the wasp, _Polistes_, Hubbard has observed that a single individual may bear eight or ten individuals of its Strepsipteron (_Xenos_, n. sp.?).
[Illustration: Fig. 154—Young larva of _Stylops_ on a bee's-hair. Greatly magnified. (After Newport.)]
There is no exact information as to how the young triungulins find their way to the bee-larvae they live in. Here again the discrepancy of opinion that prevails is probably due to great {301}difference really existing as to the method. When a _Stylops_ carried by an Insect (a Hymenopteron, be it noted, for we have no information whatever as to Hemiptera) produces young, they cover the body of the host as if it were powdered, being excessively minute and their numbers very great; many hundreds, if not thousands, of young being produced by a single _Stylops_. The species of the wasp genus _Polistes_ are specially subject to the attacks of _Stylops_; they are social Insects, and a stylopised specimen being sickly does not as a rule leave the nest; in this case the _Stylops_ larva may therefore have but little difficulty in finding its way to a Hymenopterous larva, for even though it may have to live for months before it has the chance of attaching itself to a nest-building female, yet it is clearly in the right neighbourhood. The bee genus _Andrena_ has, however, quite different habits; normally a single female makes her nest underground; but in the case of a stylopised female it is certain that no nest is built, and no larvae produced by a stylopised example, so that the young triungulins must leave the body of the bee in order to come near their prey. They can be
## active, and have great powers of leaping, so that it is perhaps in this way
possible for them to attach themselves to a healthy female bee.
[Illustration: Fig. 155.—Portion of early stages of _Xenos rossii_. (After von Siebold.) A, Small male larva; B, small female larva; C, full-grown male larva; D, full-grown female larva; E, the so-called "cephalothorax" and adjacent segment of adult female. (The newly-hatched larva is very much like that of _Stylops_ shown in Fig. 154.)]
We have still only very imperfect knowledge as to the structure and development of Strepsiptera. Indeed but little information has been obtained since 1843.[160] Before that time the mature female was supposed to be a larva, and the triungulins found in it to be parasites. Although the erroneous character of these views has been made clear, the problems that have been suggested present great difficulties. Apparently the change from the triungulin condition (Fig. 154) to the parasitic larvae (Fig. 155, A, B) is extremely great and abrupt, and it appears also that during {302}the larval growth considerable sexual differentiation occurs (Fig. 155, C, D); details are, however, wanting, and there exists but little information as to the later stages. Hence it is scarcely a matter for surprise that authorities differ as to which is the head and which the anal extremity of the adult female. Von Siebold apparently entertained no doubt as to the part of the female that is extruded being the anterior extremity; indeed he called it a cephalothorax. Supposing this view to be correct, we are met by the extraordinary facts that the female extrudes the head for copulatory purposes, that the genital orifice is placed thereon, and that the young escape by it. Meinert[161] contends that the so-called cephalothorax of the adult is the anal extremity, and that fertilisation and the escape of the young are effected by the natural passages, the anterior parts of the body being affected by a complete degeneration. Nassonoff, in controversion of Meinert, has recently pointed out that the "cephalothorax" of the young is shown by the nervous system to be the anterior extremity. It still remains, however, to be shewn that the "cephalothorax" of the adult female corresponds with that of the young, and we shall not be surprised if Meinert prove to be correct. The internal anatomy and the processes of oogenesis appear to be of a very unusual character, but their details are far from clear. Brandt has given some
## particulars as to the nervous system; though he does not say whether taken
from the male or female, we may presume it to be from the former; there is a supra-oesophageal ganglion, and near it a large mass which consists of two parts, the anterior representing the sub-oesophageal and the first thoracic ganglia, while the posterior represents two of the thoracic and most of the abdominal ganglia of other Insects; at the posterior extremity, connected with the other ganglia by a very long and slender commissure, there is another abdominal ganglion.[162]
It is a matter of great difficulty to procure material for the prosecution of this study; the fact that the instars to be observed exist only in the interior of a few Hymenopterous larvae, which in the case of the bee, _Andrena_, are concealed under ground; and in the case of the wasps, _Polistes_, placed in cells in a nest of wasps, adds greatly to the difficulty. It is therefore of interest to know that Strepsiptera occur in Insects with incomplete {303}metamorphosis. They have been observed in several species of Homoptera; and the writer has a large Pentatomid bug of the genus _Callidea_, which bears a female Strepsipteron apparently of large size. This bug[163] is abundant and widely distributed in Eastern Asia, and it may prove comparatively easy to keep stylopised examples under observation. Both v. Siebold and Nassonoff think parthenogenesis occurs in Strepsiptera, but there appear to be no facts to warrant this supposition. Von Siebold speaks of the phenomena of Strepsipterous reproduction as paedogenesis, or pseudo-paedogenesis, but we must agree with Meinert that they cannot be so classed.
The males of Strepsiptera live for only a very short time, and are very difficult of observation. According to Hubbard the males of _Xenos_ dash about so rapidly that the eye cannot see them, and they create great agitation amongst the wasps in the colonies of which they are bred. Apparently they are produced in great numbers, and their life consists of only fifteen or twenty minutes of fiery energy. The males of _Stylops_ are not exposed to such dangers as those of _Xenos_, and apparently live somewhat longer—a day or two, and even three days are on record. The individuals of _Andrena_ parasitised by _Stylops_ are apparently greatly affected in their economy and appear earlier in the season than other individuals; this perhaps may be a reason, coupled with their short lives, for their being comparatively rarely met with by entomologists.
[Illustration: Fig. 156.—Abdomen of a wasp (_Polistes hebraeus_) with a Strepsipteron (_Xenos_ ♀) in position, one of the dorsal plates of the wasp's abdomen being removed. _a_, Projection of part of the parasite; _b_, line indicating the position of the removed dorsal plate.]
It is not possible at present to form a valid opinion as to whether Stylopidae are a division of Coleoptera or a separate Order. Von Siebold considered them a distinct Order, and Nassonoff, who has recently discussed the question, is also of that opinion.
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