Part 19

The _Silphidae_, or carrion beetles, form one of the best-known families of this group. They are rotund or elongate insects with conical front haunches, the elytra generally covering (fig. 10) the whole dorsal region of the abdomen, but sometimes leaving as many as four terga exposed (fig. 11). Some of these beetles are brightly coloured, while others are dull black. They are usually found in carrion, and the species of _Necrophorus_ (fig. 11) and _Necrophaga_ are valuable scavengers from their habit of burying small vertebrate carcases which may serve as food for their larvae. At this work a number of individuals are associated together. The larvae that live underground have spiny dorsal plates, while those of the _Silpha_ (fig. 10) and other genera that go openly about in search of food resemble wood-lice. About 1000 species of _Silphidae_ are known. Allied to the _Silphidae_ are a number of small and obscure families, for which reference must be made to monographs of the order. Of special interest among these are the _Histeridae_, compact beetles (fig. 12) with very hard cuticle and somewhat abbreviated elytra, with over 2000 species, most of which live on decaying matter, and the curious little _Pselaphidae_, with three-segmented tarsi, elongate palpi, and shortened abdomen; the latter are usually found in ants' nests, where they are tended by the ants, which take a sweet fluid secreted among little tufts of hair on the beetles' bodies; these beetles, which are carried about by the ants, sometimes devour their larvae. The _Trichopterygidae_, with their delicate narrow fringed wings, are the smallest of all beetles, while the _Platypsyllidae_ consist of only a single species of curious form found on the beaver.

[Illustration: FIG. 12. _Hister iv-maculatus_ (Mimic Beetle). Europe.]

[Illustration: FIG. 13. _Oxyporus rufus_. Europe.]

[Illustration: FIG. 14. _Stenus biguttatus_. Europe.]

The _Staphylinidae_, or rove-beetles--a large family of nearly 10,000 species--may be known by their very short elytra, which cover only two of the abdominal segments, leaving the elongate hind-body with seven or eight exposed, firm terga (figs. 13, 14). These segments are very mobile, and as the rove-beetles run along they often curl the abdomen upwards and forwards like the tail of a scorpion. The _Staphylinid_ larvae are typically campodeiform. Beetles and larvae are frequently carnivorous in habit, hunting for small insects under stones, or pursuing the soft-skinned grubs of beetles and flies that bore in woody stems or succulent roots. Many _Staphylinidae_ are constant inmates of ants' nests.

MALACODERMATA.--In this tribe may be included a number of families distinguished by the softness of the cuticle, the presence of seven or eight abdominal sterna and of four malpighian tubes, and the firm, well-armoured larva (fig. 15, c) which is often predaceous in habit. The mesothoracic epimera bound the coxal cavities of the intermediate legs. The _Lymexylonidae_, a small family of this group, characterized by its slender, undifferentiated feelers and feet, is believed by Lameere to comprise the most primitive of all living beetles, and Sharp lays stress on the undeveloped structure of the tribe generally.

[Illustration: FIG. 15.--Glow-worm. _Lampyris noctiluca_. a, Male; b, female; c, larva (ventral view). Europe.]

The _Lampyridae_ are a large family, of which the glow-worm (_Lampyris_) and the "soldier beetles" (_Telephorus_) are familiar examples. The female "glow-worm" (fig. 15, b), emitting the well-known light (see above), is wingless and like a larva; the luminosity seems to be an attraction to the male, whose eyes are often exceptionally well developed. Some male members of the family have remarkably complex feelers. In many genera of _Lampyridae_ the female can fly as well as the male; among these are the South European "fireflies."

TRICHODERMATA.--Several families of rather soft-skinned beetles, such as the _Melyridae_, _Cleridae_ (fig. 16), _Corynetidae_, _Dermestidae_ (fig. 17), and _Dascillidae_, are included in this tribe. They may be distinguished from the Malacodermata by the presence of only five or six abdominal sterna, while six malpighian tubes are present in some of the families. The beetles are hairy and their larvae well-armoured and often predaceous. Several species of _Dermestidae_ are commonly found in houses, feeding on cheeses, dried meat, skins and other such substances. The "bacon beetle" (_Dermestes lardarius_), and its hard hairy larva, are well known. According to Sharp, all Dermestid larvae probably feed on dried animal matters; he mentions one species that can find sufficient food in the horsehair of furniture, and another that eats the dried insect-skins hanging in old cobwebs.

[Illustration: FIG. 16.--_Clerus apiarus_ (Hive Beetle). Europe.]

[Illustration: FIG. 17.--_Dermestes lardarius_ (Bacon Beetle).]

STERNOXIA.--This is an important tribe of beetles, including families with four malpighian tubes and only five or six abdominal sterna, while in the thorax there is a backwardly directed process of the prosternum that fits into a mesosternal cavity. The larvae are elongate and worm-like, with short legs but often with hard strong cuticle.

[Illustration: FIG. 18.--A, Wireworm; B, pupa of Click Beetle; C, adult Click Beetle (_Agriotes lineatum_).]

The _Elateridae_ or click beetles (fig. 18) have the prosternal process just mentioned, capable of movement in and out of the mesosternal cavity, the beetles being thus enabled to leap into the air, hence their popular name of "click-beetles" or "skip-jacks." The prothorax is convex in front, and is usually drawn out behind into a prominent process on either side, while the elytra are elongate and tapering. Many of the tropical American _Elateridae_ emit light from the spots on the prothorax and an area beneath the base of the abdomen; these are "fireflies" (see above). The larvae of _Elateridae_ are elongate, worm-like grubs, with narrow bodies, very firm cuticle, short legs, and a distinct anal proleg. They are admirably adapted for moving through the soil, where some of them live on decaying organic matter, while others are predaceous. Several of the elaterid larvae, however, gnaw roots and are highly destructive to farm crops. These are the well-known "wire-worms" (q.v.).

[Illustration: FIG. 19.--_Catoxantha bicolor_. Java.]

The _Buprestidae_ are distinguished from the _Elateridae_ by the immobility of the prosternal process in the mesosternal cavity and by the absence of the lateral processes at the hind corners of the prothorax. Many tropical _Buprestidae_ are of large size (fig. 19), and exhibit magnificent metallic colours; their elytra are used as ornaments in human dress. The larvae are remarkable for their small head, very broad thorax, with reduced legs, and narrow elongate abdomen. They feed by burrowing in the roots and stems of plants.

BOSTRYCHOIDEA.--This tribe is distinguished from the Malacoderma and allied groups by the mesothoracic epimera not bounding the coxal cavities of the intermediate legs. The downwardly directed head is covered by the pronotum, and the three terminal antennal segments form a distinct club. To this group belong the _Bostrychidae_ and _Ptinidae_, well known (especially the latter family) for their ravages in old timber. The larvae are stout and soft-skinned, with short legs in correlation with their burrowing habit. The noises made by some _Ptinidae_ (_Anobium_) tapping on the walls of their burrows with their mandibles give rise to the "death tick" that has for long alarmed the superstitious.

[Illustration: FIG. 20.--_Hydrophilus piceus_ (Black Water Beetle). Europe.]

CLAVICORNIA.--This is a somewhat heterogeneous group, most of whose members are characterized by clubbed feelers and simple, unbroadened tarsal segments--usually five on each foot--but in some families and genera the males have less than the normal number on the feet of one pair. There are either four or six malpighian tubes. A large number of families, distinguished from each other by more or less trivial characters, are included here, and there is considerable diversity in the form of the larvae. The best-known family is the _Hydrophilidae_, in which the feelers are short with less than eleven segments and the maxillary palpi very long. Some members of this family--the large black _Hydrophilus piceus_ (fig. 20), for example--are specialized for an aquatic life, the body being convex and smooth as in the _Dyticidae_, and the intermediate and hind-legs fringed for swimming. When _Hydrophilus_ dives it carries a supply of air between the elytra and the dorsal surface of the abdomen, while air is also entangled in the pubescence which extends beneath the abdomen on either side, being scooped in bubbles by the terminal segments of the feelers when the insect rises to the surface. Many of the _Hydrophilidae_ construct, for the protection of their eggs, a cocoon formed of a silky material derived from glands opening at the tip of the abdomen. That of _Hydrophilus_ is attached to a floating leaf, and is provided with a hollow, tapering process, which projects above the surface and presumably conveys air to the enclosed eggs. Other _Hydrophilidae_ carry their egg-cocoons about with them beneath the abdomen. Many _Hydrophilidae_, unmodified for aquatic life, inhabit marshes. The larvae in this family are well-armoured, active and predaceous. Of the numerous other families of the Clavicornia may be mentioned the _Cucujidae_ and _Cryptophagidae_, small beetles, examples of which may be found feeding on stored seeds or vegetable refuse, and the _Mycetophagidae_, which devour fungi. The _Nitidulidae_ are a large family with 1600 species, among which members of the genus _Meligethes_ are often found in numbers feeding on blossoms, while others live under the bark of trees and prey on the grubs of boring beetles.

HETEROMERA.--This tribe is distinguished by the presence of the normal five segments in the feet of the fore and intermediate legs, while only four segments are visible in the hind-foot. Considerable diversity is to be noticed in details of structure within this group, and for an enumeration of all the various families which have been proposed and their distinguishing characters the reader is referred to one of the monographs mentioned below. Some of the best-known members of the group belong to the _Tenebrionidae_, a large family containing over 10,000 species and distributed all over the world. The tenebrionid larva is elongate, with well-chitinized cuticle, short legs and two stumpy tail processes, the common mealworm (fig. 21) being a familiar example. Several species of this family are found habitually in stores of flour or grain. The beetles have feelers with eleven segments, whereof the terminal few are thickened so as to form a club. The true "black-beetles" or "churchyard beetles" (_Blaps_) (fig. 22) belong to this family; like members of several allied genera they are sooty in colour, and somewhat resemble ground beetles (_Carabi_) in general appearance.

[Illustration: FIG. 21.--(a) _Tenebrio molitor_ (Flour Beetle). Europe. (b) Larva, or mealworm.]

[Illustration: FIG. 22.--_Blaps mortisaga_ (Churchyard Beetle). Europe.]

[Illustration: FIG. 23.--_Meloe proscarabaeus_ (Oil Beetle). Europe.]

[Illustration: FIG. 24.--_Lytta vesicatoria_ (Blister Beetle). Europe.]

The most interesting of the Heteromera, and perhaps of all the Coleoptera, are some beetles which pass through two or more larval forms in the course of the life-history (hypermetamorphosis). These belong to the families _Rhipidophoridae_ and _Meloidae_. The latter are the oil beetles (fig. 23) or blister beetles (fig. 24), insects with rather soft cuticle, the elytra (often abbreviated) not fitting closely to the sides of the abdomen, the head constricted behind the eyes to form a neck, and the claws of the feet divided to the base. Several of the _Meloidae_ (such as the "Spanish fly," fig. 24) are of economic importance, as they contain a vesicant substance used for raising medicinal blisters on the human skin. The wonderful transformations of these insects were first investigated by G. Newport in 1851, and have recently been more fully studied by C. V. Riley (1878) and J. H. Fabre. The first larval stage is the "triungulin," a tiny, active, armoured larva with long legs (each foot with three claws) and cercopods. In the European species of _Sitaris_ and _Meloe_ these little larvae have the instinct of clinging to any hairy object. All that do not happen to attach themselves to a bee of the genus _Anthophora_ perish, but those that succeed in reaching the right host are carried to the nest, and as the bee lays an egg in the cell the triungulin slips off her body on to the egg, which floats on the surface of the honey. After eating the contents of the egg, the larva moults and becomes a fleshy grub with short legs and with paired spiracles close to the dorsal region, so that, as it floats in and devours the honey, it obtains a supply of air. After a resting (pseudo-pupal) stage and another larval stage, the pupa is developed. In the American EPICAUTA VITTATA the larva is parasitic on the eggs and egg-cases of a locust. The triungulin searches for the eggs, and, after a moult, becomes changed into a soft-skinned tapering larva. This is followed by a resting (pseudo-pupal) stage, and this by two successive larval stages like the grub of a chafer. The RHIPIDOPHORIDAE are beetles with, short elytra, the feelers pectinate in the males and serrate in the females. The life-history of _Metoecus_ has been studied by T. A. Chapman, who finds that the eggs are laid in old wood, and that the triungulin seeks to attach itself to a social wasp, who carries it to her nest. There it feeds first as an internal parasite of the wasp-grub, then bores its way out, moults and devours the wasp larva from outside. The wasps are said to leave the larval or pupal _Metoecus_ unmolested, but they are hostile to the developed beetles, which hasten to leave the nest as soon as possible.

STREPSIPTERA.--Much difference of opinion has prevailed with regard to the curious, tiny, parasitic insects included in this division, some authorities considering that they should be referred to a distinct order, while others would group them in the family _Meloidae_ just described. While from the nature of their life-history there is no doubt that they have a rather close relationship to the _Meloidae_, their structure is so remarkable that it seems advisable to regard them as at least a distinct tribe of Coleoptera.

They may be comprised in a single family, the _Stylopidae_. The males are very small, free-flying insects with the prothorax, mesothorax and elytra greatly reduced, the latter appearing as little, twisted strips, while the metathorax is relatively large, with its wings broad and capable of longitudinal folding. The feelers are branched and the jaws vestigial. The female is a segmented, worm-like creature, spending her whole life within the body of the bee, wasp or bug on which she is parasitic. One end of her body protrudes from between two of the abdominal segments of the host; it has been a subject of dispute whether this protruded end is the head or the tail, but there can be little doubt that it is the latter. While thus carried about by the host-insect, the female is fertilized by the free-flying male, and gives birth to a number of tiny triungulin larvae. The chief points in the life-history of _Stylops_ and _Xenos_, which are parasitic on certain bees (_Andrena_) and wasps (_Polistes_), have been investigated by K. T. E. von Siebold (1843) and N. Nassonov (1892). The little triungulins escape on to the body of the bee or wasp; then those that are to survive must leave their host for a non-parasitized insect. Clinging to her hairs they are carried to the nest, where they bore into the body of a bee or wasp larva, and after a moult become soft-skinned legless maggots. The growth of the parasitic larva does not stop the development of the host-larva, and when the latter pupates and assumes the winged form, the stylopid, which has completed its transformation, is carried to the outer world. The presence of a _Stylops_ causes derangement in the body of its host, and can be recognized by various external signs. Other genera of the family are parasitic on Hemiptera--bugs and frog-hoppers--but nothing is known as to the details of their life-history.

LAMELLICORNIA.--This is a very well-marked tribe of beetles, characterized by the peculiar elongation and flattening of three or more of the terminal antennal segments, so that the feeler seems to end in a number of leaf-like plates, or small comb-teeth (fig. 26, b, c). The wings are well developed for flight, and there is a tendency in the group, especially among the males, towards an excessive development of the mandibles or the presence of enormous, horn-like processes on the head or pronotum. There are four malpighian tubes. The larvae are furnished with large heads, powerful mandibles and well-developed legs, but the body-segments are feebly chitinized, and the tail-end is swollen. They feed in wood or spend an underground life devouring roots or animal excrement.

The _Lucanidae_ or stag beetles (figs. 1 and 25) have the terminal antennal segments pectinate, and so arranged that the comb-like part of the feeler cannot be curled up, while the elytra completely cover the abdomen. There are about 600 species in the family, the males being usually larger than the females, and remarkable for the size of their mandibles. In the same species, however, great variation occurs in the development of the mandibles, and the breadth of the head varies correspondingly, the smallest type of male being but little different in appearance from the female. The larvae of _Lucanidae_ live within the wood of trees, and may take three or four years to attain their full growth. The _Passalidae_ are a tropical family of beetles generally considered to be intermediate between stag-beetles and chafers, the enlarged segments of the feeler being capable of close approximation.

The _Scarabaeidae_ or chafers are an enormous family of about 15,000 species. The plate-like segments of the feeler (fig. 26, b, c) can be brought close together so as to form a club-like termination; usually the hinder abdominal segments are not covered by the elytra. In this family there is often a marked divergence between the sexes; the terminal antennal segments are larger in the male than in the female, and the males may carry large spinous processes on the head or prothorax, or both. These structures were believed by C. Darwin to be explicable by sexual selection. The larvae have the three pairs of legs well developed, and the hinder abdominal segments swollen. Most of the _Scarabaeidae_ are vegetable-feeders, but one section of the family--represented in temperate countries by the dor-beetles (_Geotrupes_) (fig. 28) and _Aphodius_, and in warmer regions by the "sacred" beetles of the Egyptians (_Scarabaeus_) (fig. 27), and allied genera--feed both in the adult and larval stages, on dung or decaying animal matter. The heavy grubs of _Geotrupes_, their swollen tail-ends black with the contained food-material, are often dug up in numbers in well-manured fields. The habits of _Scarabaeus_ have been described in detail by J. H. Fabre. The female beetle in spring-time collects dung, which she forms into a ball by continuous rolling, sometimes assisted by a companion. This ball is buried in a suitable place, and serves the insect as a store of food. During summer the insects rest in their underground retreats, then in autumn they reappear to bury another supply of dung, which serves as food for the larvae. Fabre states that the mother-insect carefully arranges the food-supply so that the most nutritious and easily digested portion is nearest the egg, to form the first meal of the young larva. In some species of _Copris_ it is stated that the female lays only two or three eggs at a time, watching the offspring grow to maturity, and then rearing another brood.

[Illustration: FIG. 25.--_Cladognathus cinnamomeus_. Java.]

[Illustration: FIG. 26.--_Melolontha fullo_ (Cockchafer). S. Europe, b, Antenna of male; c, antenna of female.]

[Illustration: FIG. 27.--_Scarabaeus Aegyptiorum_. Africa.]

[Illustration: FIG. 28.--_Geotrupes Blackburnei_. N. America.]

[Illustration: FIG. 29.--_Phaneus Imperator_. S. America.]

[Illustration: FIG. 30.--_Cetonia Baxii_. W. Africa.]

Among the vegetable-feeding chafers we usually find that while the perfect insect devours leaves, the larva lives underground and feeds on roots. Such are the habits of the cockchafer (_Melolontha vulgaris_) and other species that often cause great injury to farm and garden crops (see CHAFER). Many of these insects, such as the species of _Phanaeus_ (fig. 29) and _Cetonia_ (fig. 30), are adorned with metallic or other brilliant colours. The African "goliath-beetles" (fig. 31) and the American "elephant-beetles" (_Dynastes_) are the largest of all insects.

ANCHISTOPODA.--The families of beetles included by Kolbe in this group are distinguished by the possession of six malpighian tubes, and a great reduction in one or two of the tarsal segments, so that there seem to be only four or three segments in each foot; hence the names _Tetramera_ and _Trimera_ formerly applied to them. The larvae have soft-skinned bodies sometimes protected by rows of spiny tubercles, the legs being fairly developed in some families and greatly reduced or absent in others. As might be expected, degeneration in larval structure is correlated with a concealed habit of life.

The _Coccinellidae_, or ladybirds (fig. 32), are a large family of beetles, well known by their rounded convex bodies, usually shining and hairless. They have eleven segments to the feeler, which is clubbed at the tip, and apparently three segments only in each foot. Ladybirds are often brightly marked with spots and dashes, their coloration being commonly regarded as an advertisement of inedibility. The larvae have a somewhat swollen abdomen, which is protected by bristle-bearing tubercles. Like the perfect insects, they are predaceous, feeding on plant-lice (_Aphidae_) and scale insects (_Coccidae_). Their role in nature is therefore beneficial to the cultivator. The _Endomychidae_ (fig. 33), an allied family, are mostly fungus-eaters. In the _Erotylidae_ and a few other small related families the feet are evidently four-segmented.

[Illustration: FIG. 31.--_Goliathus giganteus_ (Goliath Beetle).]

[Illustration: FIG. 32.--_Anatio ocellata_ (Eyed Ladybird). Europe.]

[Illustration: FIG. 33.--_Endomychus coccineus_. Europe.]

[Illustration: FIG. 34.--_Sagra cyanea_. W. Africa.]

[Illustration: FIG. 35.--_Eumorphus ivguttatus_. Sumatra.]

[Illustration: FIG. 36.--_Lophonocerus barbicornis_. S. America.]

The _Chrysomelidae_, or leaf-beetles (figs. 34, 35), are a very large family, with "tetramerous" tarsi; there seem to be only four segments to the foot, but there are really five, the fourth being greatly reduced. The mandibles are strong, adapted for biting the vegetable substances on which these beetles feed, and the palps of the second maxillae have three segments. Most of the _Chrysomelidae_ are metallic in colour and convex in form; in some the head is concealed beneath the prothorax, and the so-called "tortoise" beetles (_Cassidinae_) have the elytra raised into a prominent median ridge. The most active form of larva found in this family resembles in shape that of a ladybird, tapering towards the tail end, and having the trunk segments protected by small firm sclerites. Such larvae, and also many with soft cuticle and swollen abdomen--those of the notorious "Colorado beetle," for example--feed openly on foliage. Others, with soft, white, cylindrical bodies, which recall the caterpillars of moths, burrow in the leaves or stems of plants. The larvae of the tortoise-beetles have the curious habit of forming an umbrella-like shield out of their own excrement, held in position by the upturned tail-process. The larvae of the beautiful, elongate, metallic _Donaciae_ live in the roots and stems of aquatic plants, obtaining thence both food and air. The larva pierces the vessels of the plant with sharp processes at the hinder end of its body. In this way it is believed that the sub-aqueous cocoon in which the pupal stage is passed becomes filled with air.