CHAPTER II

HYMENOPTERA ACULEATA _CONTINUED_—DIVISION II. DIPLOPTERA OR WASPS— EUMENIDAE, SOLITARY TRUE WASPS—VESPIDAE, SOCIAL WASPS—MASARIDAE

DIVISION II. DIPLOPTERA—WASPS.

_Anterior wings longitudinally plicate in repose; the pronotum extending back, so as to form on each side an angle reposing on the tegula; the basal segments of the hind body not bearing nodes or scales; the hind tarsi formed for simple walking. The species either solitary or social in their habits; some existing in three forms, males, females, and workers._

[Illustration: Fig. 26—Upper aspect of pronotum and mesonotum of a wasp, _Eumenes coarctata_. _a_, Angle of pronotum; _b_, tegula; _c_, base of wing; _d_, mesonotum.]

This division of Hymenoptera includes the true wasps, but not the fossorial wasps. The name applied to it has been suggested by the fact that the front wings become doubled in the long direction when at rest, so as to make them appear narrower than in most other Aculeata (Fig. 27). This character is unimportant in function so far as we know,[40] and it is not quite constant in the division, since some of the Masaridae do not exhibit it. The character reappears outside the Diploptera in the genus _Leucospis_—a member of the Chalcididae in the parasitic series of Hymenoptera—the species of which greatly resemble wasps in coloration. A better character is that furnished by the well-marked angle, {72}formed by the pronotum on the dorsal part (Fig. 26). By a glance at this part a Diplopterous Insect can always be readily distinguished.

Three families are at present distinguished in the Diploptera, viz. Eumenidae, Vespidae and Masaridae. We anticipate that Eumenidae and Vespidae will ultimately be found to constitute but one family.

FAM. 1. EUMENIDAE—SOLITARY TRUE WASPS.

_Claws of the feet toothed or bifid; middle tibiae with only one spur at tip. Social assemblages are not formed, and there is no worker-caste, the duties of nest-construction, etc., being performed solely by the female._

The Eumenidae, or solitary wasps, are very little noticed by the ordinary observer, but they are nevertheless more numerous than the social Vespidae, about 800 species being known. In Britain we have sixteen species of the solitary, as against seven of the social wasps. The Eumenidae exhibit a considerable diversity in form and structure; some of them have the pedicel at the base of the abdomen very elongate, while in others this is so short as to be imperceptible in the ordinary position of the body. A repetition of similar differences of form occurs in the social wasps, so that notwithstanding the difference in habits there seems to be no satisfactory way of distinguishing the members of the two families except by the structure of the claws and tibial spurs.

[Illustration: Fig. 27.—_Eumenes flavopicta_ ♀. Burma. The wings on the left in the position of repose, to show folding.]

Fabre has sketched the habits of a species of _Eumenes_, probably _E. pomiformis_. This _Eumenes_ constructs with clay a small vase-like earthenware vessel, in the walls of which small stones are embedded (like Fig. 28, B). This it fills with food for the young. The food consists of caterpillars to the number of fourteen or sixteen for each nest. These caterpillars are believed to be stung by the parent-wasp (as is the case in the {73}fossorial Hymenoptera), but complete evidence of this does not seem to be extant, and if it be so, the stinging does not completely deprive the caterpillars of the capacity of movement, for they possess the power of using their mandibles and of making strokes, or kicking with the posterior part of the body. It is clear that if the delicate egg of the _Eumenes_ or the delicate larva that issues from it were placed in the midst of a mass of this kind, it would probably suffer destruction; therefore, to prevent this, the egg is not placed among the caterpillars, but is suspended from the dome covering the nest by a delicate thread rivalling in fineness the web of the spider, and being above the mass of food it is safe. When the young larva leaves the egg it still makes use of the shell as its habitation, and eats its first meals from the vantage-point of this suspension; although the mass of the food grows less by consumption, the little larva is still enabled to reach it by the fact that the egg-shell splits up to a sort of ribbon, and thus adds to the length of the suspensory thread, of which it is the terminal portion. Finally the heap of caterpillars shrinks so much that it cannot be reached by the larva even with the aid of the augmented length of the suspensory thread; by this time, however, the little creature has so much increased in size and strength that it is able to take its place amongst the food without danger of being crushed by the mass, and it afterwards completes its metamorphosis in the usual manner.

[Illustration: Fig. 28—Nidification of solitary wasps: section through nest, A, of _Odynerus reniformis_; B, of _Eumenes arbustorum_. _a_, The suspended egg of the wasp; _b_, the stored caterpillars. (After André.)]

It is known that other species of _Eumenes_ construct vase-like nests; _E. unguiculata_, however, according to an imperfect account given by Perris, makes with earth a closed nest of irregular shape, containing three cells in one mass. The saliva of these builders has the power of acting as a cement, and of forming with the clay a very impenetrable material. One species, _E. coarctata_, L. of this genus occurs in Britain. The clay {74}nests (Fig. 29) of this Insect are often attached to the twigs of shrubs, while those of the two species previously mentioned are usually placed on objects that offer a large surface for fixing the foundations to, such as walls. According to Goureau the larva of this species forms in one corner of its little abode, separated by a partition, a sort of dust-heap in which it accumulates the various débris resulting from the consumption of its stores.

_Eumenes conica_, according to Horne, constructs in Hindostan clay-nests with very delicate walls. This species provisions its nest with ten or twelve green caterpillars; on one occasion this observer took from one cell eight green caterpillars and one black. It is much attacked by parasites owing, it is thought, to the delicacy of the walls of the cells, which are easily pierced; from one group of five cells two specimens only of the _Eumenes_ were reared.

[Illustration: Fig. 29—Nest of _Eumenes coarctata_: A, the nest attached to wood; B, detached, showing the larva. _a_, the larva; _b_, the partition of the cell. (After André.)]

_Odynerus_, with numerous sub-genera, the names of which are often used as those of distinct genera, includes the larger part of the solitary wasps; it is very widely distributed over the earth, and is represented by many peculiar species even in the isolated Archipelago of Hawaii; in Britain we have about fifteen species of the genus. The _Odynerus_ are less accomplished architects than the species of _Eumenes_, and usually play the more humble parts of adapters and repairers; they live either in holes in walls, or in posts or other woodwork, or in burrows in the earth, or in stems of plants. Several species of the sub-genus _Hoplopus_ have the remarkable habit of constructing burrows in sandy ground, and forming at their entry a curvate, freely projecting tube placed at right angles to the main burrow, and formed of the grains of sand brought out by the Insect during excavation and cemented together. The habits of one such species were described by Réaumur, of another by Dufour; and recently Fabre has added to the accounts of these naturalists some important information drawn from his own observations on _O. reniformis_.

{75}[Illustration: Fig. 30.—_Odynerus antilope_ ♀. Britain.]

This Insect provisions its cell with small caterpillars to the number of twenty or upwards (Fig. 28, A.) The egg is deposited before the nest is stocked with food; it is suspended in such a manner that the suspensory thread allows the egg to reach well down towards the bottom of the cell. The caterpillars placed as food in the nest are all curled up, each forming a ring approximately adapted to the calibre of the cell. Fabre believes these caterpillars to be partly stupefied by stinging, but the act has not been observed either by himself, Réaumur, or Dufour. The first caterpillar is eaten by the wasp-larva from its point of suspension; after this first meal has been made the larva is supposed to undergo a change of skin; it then abandons the assistance of the suspensory thread, taking up a position in the vacant chamber at the end of the cell and drawing the caterpillars to itself one by one. This arrangement permits the caterpillars to be consumed in the order in which they were placed in the cell, so that the one that is weakest on account of its longer period of starvation is first devoured. Fabre thinks all the above points are essential to the successful development of this wasp-larva, the suspension protecting the egg and the young larva from destruction by pressure or movement of the caterpillars, while the position of the larva when it leaves the thread and takes its place on the floor of the cell ensures its consuming the food in the order of introduction; besides this the caterpillars used are of a proper size and of a species the {76}individuals of which have the habit of rolling themselves up in a ring; while, as the calibre of the tube is but small, they are unable to straighten themselves and move about, so that their consumption in proper order is assured. Some interesting points in the habits of an allied species, _O._ (_Pterocheilus_) _spinipes_ have been observed by Verhoeff; the facts as regards the construction and provisioning of the cell are almost the same as in _O. reniformis_. The species of _Odynerus_ are very subject to the attacks of parasites, and are, it is well known, destroyed to an enormous extent by Chrysididae. Verhoeff says that the wasp in question supplied food much infested by entoparasites; further, that a fly, _Argyromoeba sinuata_, takes advantage of the habit of the _Odynerus_ of leaving its nest open during the process of provisioning, and deposits also an egg in the nest; the _Odynerus_ seems, however, to have no power of discovering the fact, or more probably has no knowledge of its meaning, and so concludes the work of closing the cell in the usual way; the egg of the _Argyromoeba_ hatches, and the maggot produced feeds on the caterpillars the wasp intended for its own offspring. Verhoeff observed that the egg of the wasp-larva is destroyed, but he does not know whether this was done by the mother _Argyromoeba_ or by the larva hatched from her egg. Fabre's observations on allied species of Diptera render it, however, highly probable that the destruction is effected by the young fly-larva and not by the mother-fly.

Mr. R. C. L. Perkins once observed several individuals of our British _O. callosus_ forming their nests in a clay bank, and provisioning them with larvae, nearly all of which were parasitised, and that to such an extent as to be evident both to the eye and the touch. In a few days after the wasps' eggs were laid, swarms of the minute parasites emerged and left no food for the _Odynerus_. Curiously, as it would seem, certain of the parasitised and stored-up larvae attempted (as parasitised larvae not infrequently do), to pupate. From which, as Mr. Perkins remarks, we may infer that (owing to distortion) the act of paralysing by the wasp had been ineffectual. Mr. Perkins has also observed that some of the numerous species of Hawaiian _Odynerus_ make a single mud-cell, very like the pot of an _Eumenes_, but cylindrical instead of spherical. This little vessel is often placed in a leaf that a spider curls up; young molluscs of the genus _Achatinella_ also {77}avail themselves of this shelter, so that a curious colony is formed, consisting of the _Odynerus_ in its pot, of masses of the young spiders, and of the little molluscs.

Horne has recorded that the East Indian _O. punctum_ is fond of availing itself of holes in door-posts where large screws have been; after the hole has been filled with provisions, the orifice is covered over level with the surface of the wood so that it eludes human observation. It is nevertheless discovered by an Ichneumon-fly which pierces the covering with its ovipositor and deposits an egg within.

The genus _Abispa_ is peculiar to Australia and includes some very fine solitary wasps, having somewhat the appearance of very large _Odynerus_: these Insects construct a beautiful nest with a projecting funnel-shaped entrance, and of so large a size that it might pass for the habitation of a colony of social wasps; it appears, however, that this large nest is really formed by a single female.

The species of the genus _Rhygchium_ are also of insecticide habits, and appear to prefer the stems of pithy plants as the nidus for the development of the generation that is to follow them. Lichtenstein says that a female of the European _R. oculatum_ forms fifteen to twenty cells in such a situation, and destroys 150 to 200 caterpillars, and he suggests that, as it is easy to encourage these wasps to nest in a suitable spot, we should utilise them to free our gardens from caterpillars, as we do cats to clear the mice from our apartments.

The East Indian _R. carnaticum_ seems to have very similar habits to its European congener, adapting for its use the hollow stems of bamboos. Horne has recorded a case in which a female of this species took possession of a stem in which a bee, _Megachile lanata_, had already constructed two cells; it first formed a partition of mud over the spot occupied by the bee, this

## partition being similar to that which it makes use of for separating the

spaces intended for its own young. This species stores caterpillars for the benefit of its larvae, and this is also the case with another Eastern species, _R. nitidulum_. This latter Insect, however, does not nidificate in the stems of plants, but constructs clay cells similar to those of _Eumenes_, and fixes them firmly to wood. _Rhygchium brunneum_ is said by Sir Richard Owen to obliterate hieroglyphic inscriptions in Egypt by its habit of building mud {78}nests amongst them. An individual of this wasp was found by Dr. Birch when unrolling a mummy—"There being every reason to believe that the Insect had remained in the position in which it was found ever since the last rites were paid to the ancient Egyptian."

FAM. 2. VESPIDAE—SOCIAL WASPS.

_Claws of the feet simple, neither toothed nor bifid, middle tibiae with two spurs at the tip. Insects living in societies, forming a common dwelling of a papery or card-like material; each generation consists of males and females and of workers—imperfect females—that assist the reproductive female by carrying on the industrial occupations._

The anterior wing possesses four submarginal cells, as in the Eumenidae. The attention of entomologists has been more directed to the habits and architecture than to the taxonomy of these Insects, so that the external structure of the Insects themselves has not been so minutely or extensively scrutinised as is desirable; de Saussure, the most important authority, bases his classification of the Insects themselves on the nature of the nests they form. These habitations consist of an envelope, protecting cells similar in form to the comb of the honey-bee, but there is this important difference between the two, that while the bee forms its comb of wax that it secretes, the wasps make use of paper or card that they form from fragments of vegetable tissue,—more particularly woody fibre—amalgamated by means of cement secreted by glands; the vegetable fragments are obtained by means of the mandibles, the front legs playing a much less important part in the economy of the Vespidæ than they do in that of the bees and fossorial Hymenoptera.

In most of the nests of Vespidæ the comb is placed in stages or stories one above the other, and separated by an intervening space, but in many cases there is only one mass of comb. It is the rule that, when the cells of the comb are only partially formed, eggs are deposited in them, and that the larva resulting from the egg is fed and tended by the mother, or by her assistants, the workers; as the larvae grow, the cells are increased in correspondence with the size of the larva; the subsequent metamorphosis to pupa and imago taking place in the cells after they have been entirely {79}closed. The food supplied is of a varied nature according to the species, being either animal or vegetable, or both.

[Illustration: Fig. 31—Section of the subterranean nest of the common wasp, _Vespa germanica_, in position. (After Janet.) _a_, One of the chambers of an ant's nest, _Lasius flavus_, placed above the wasps' nest; _b_, root to which the first attachment of the nest was made; _c_, secondary attachments; _d_, the first-made attachment; _e_, a flint within the envelopes of the nest; _f_, the chief suspensory pillar of the second layer of comb; _g_, lateral galleries; _h_, one of the secondary pillars of suspension between two layers of comb; _i_, the layers of wasp-paper forming the envelope of nest; _j_, vacant space round the nest; _k_, flints that fell to the bottom during the work of excavation; _l_, numerous larvae of a fly, _Pegomyia inanis_ (?) placed vertically in ground beneath the nest; _m^1_ to _m^7_, the layers of comb, in _m^2_ the cells are indicated, in _m^8_ (above the main figure) the arrangement of the three cells forming the commencement of the new layer of comb, _m^7_, is shown; _n_, gallery of access from surface; _o_, burrow of a mole; _p_, interval of 90 mm. between top of nest and surface; _q_, height of the nest, 163 mm.]

Although the nests of the social wasps are very elaborate constructions, yet they serve the purposes of the Insects for only a single season. This is certainly the case in our own country. Here each nest is commenced by a single female or queen; she at first performs unaided all the duties for the inauguration of the colony; she lays the foundation of the cells, deposits the eggs in them, feeds the young, and thus rears a brood of workers that at once assist her, and for the future relieve her of a considerable portion of her former occupations; the nest is by them added to and increased, till the cold weather of the autumn is at hand; at this time many males and females are produced; the cold weather either destroys the inhabitants of the nest, or reduces their vitality so that it is impossible for them to pursue successfully the avocations necessary for their subsistence, and {80}they succumb to adversity. The young females, however, hibernate, and each one that lives through the winter is the potential founder of a new nest in the way we have already described. It might be supposed that in tropical countries where no cold season occurs the phenomena would be different, that the colonies would be permanent, and that the nests would be inhabited until they were worn out. De Saussure, however, informs us that this is not the case, but that in the tropics also the colonies die off annually. "The nests are abandoned," he says, "without it being possible to discover the reason, for apparently neither diminution of temperature nor scarcity of food cause them (the Insects) to suffer. One is tempted to suppose that the death of the Insects is the result of a physiological necessity."

NESTS OF SOCIAL WASPS.—In Europe wasps' nests disappear very soon after they are deserted. As it would appear from de Saussure's conclusions that in the tropics as well as in the temperate regions the rule is that the colonies endure only a portion of one year, and that a new nest is commenced by a single founder once in twelve months, it is a somewhat remarkable fact that some tropical wasp-nests are much more durable than the lives of the inhabitants require, so that solidly constructed nests are often found hanging to the trees long after they have been deserted, and are sometimes overgrown with moss. Cuming has recorded the fact that he found in South America an old wasp-nest that had been taken possession of by swallows. We do not assign, however, much importance to the views of de Saussure, because we may anticipate that enquiry will reveal much variety in the habits of tropical and sub-tropical wasps. It is known that species exist that store up honey, after the fashion of bees, and von Ihering has recently shown[41] that in Brazil, species of several genera form new colonies by swarming, after the manner of bees. So that it is possible that certain colonies may remain for a long period in the same nest.

Much more variety exists in wasps' nests than would be supposed probable; those formed by some of the tropical species of Vespidae are enveloped in so solid and beautifully constructed an envelope of papier-maché, that they resist with complete success the torrential rains of the tropics; while some of those found in our own country are made of extremely soft and delicate paper, {81}which is probably chiefly glandular products. Our British Vespidae number only eight species, all belonging to the one genus Vespa, and yet they exhibit three different modes of nidification. _Vespa vulgaris_, _V. germanica_ and _V. rufa_ form subterranean nests, while _V. arborea_, _V. sylvestris_ and _V. norvegica_ suspend their habitations from the branches of trees, bushes, or strong annual plants. _Vespa crabro_, the hornet, usually adopts an intermediate course, forming its nest above ground, but in a spot where it is protected and concealed. The favourite habitat of this formidable Insect is the interior of an old tree, but the hornet will sometimes avail itself of the protection of a thatched roof. Both it and other arboreal species are said, however, to occasionally make subterranean nests. It is ascertained that _V. austriaca_, the eighth species, is an inquiline.

[Illustration: Fig. 32—Nest of (?) _Polybia_ sp. The envelope partly cut open; _o_, entrance. (After de Saussure.)]

De Saussure,[42] the monographer of the social wasps, classifies them according to the architecture of their nests. He establishes three groups: (1) Stelocyttares, in which the layers of comb are not connected with the envelope, but are supported by pillars made by the wasps (Fig. 31); (2) Poecilocyttares, an unsatisfactory group of which the chief characteristics appear to be that the nest is always covered by an envelope, and the comb is supported by an object such as the branch of a tree, round, or on, which the envelope is placed (Fig. 32); (3) Phragmocyttares, in which the layers of comb are supported, in part or entirely, by the envelope of the nest, communication being effected by a hole in each layer of the comb (Fig. 33). de Saussure's classification is far from satisfactory. There are many social wasps that construct nests destitute of any proper envelope; as an example of this, we may mention the species of {82}the abundant genus _Polistes_; these Insects make hexagonal cells, of paper-like material, forming an irregular comb, or mass, attached to bushes by a stalk near its centre; these nests are placed so that the mouths of the open cells look downwards. The species of _Ischnogaster_ (Fig. 34) make layers of comb, connected by a pedicel, but without any envelope; these Insects form a section of Stelocyttares called Gymnodomes.

Most of the nests of the Poecilocyttares have only a single layer of comb. The wasps of the genera _Synoeca_ and _Polybia_ have the habit of spreading a layer of cells on a leaf, or on the bark of a tree, and of covering this with an envelope that is pierced by a single orifice only, but that does not rest on the cells, and so allows circulation of the Insects between the cells and the envelope. This appears to be the arrangement in a nest of _Synoeca cyanea_ preserved in the British Museum; in this construction a large layer of cells is moulded on the branch of a tree, whose contour, for a length of two or three feet, it consequently follows; while outside the mass there is placed a continuous envelope, leaving a considerable distance between it and the cells.

It would be impossible in the space at our disposal to give a satisfactory account of all the forms of wasp-nests, and we must therefore refer the student to de Saussure's work, confining ourselves to a brief notice of some specially interesting forms. The habitation of the Brazilian _Polybia_ (_Myrapetra_) _scutellaris_ is a very solid, closed structure, covered externally with rough knobs or angular projections. Although of very large size—it may be upwards of two feet in length—it is suspended from a branch, and has but one orifice; the arrangement of the combs in the interior is that of the Phragmocyttares, they being firmly attached to the outer envelope, and so placed as to form a curved surface, the convexity of which is downwards: the number of wasps in a well-developed nest of this kind must be very great. This species is said to be a honey-gathering wasp.

One of the best known of the South American wasps' nests is the construction (Fig. 33) of _Chartergus chartarius_; these nests are so regularly shaped, and formed of papier-maché so compact and solid, as to look like stone: this edifice is attached in a very firm manner to the branch of a tree, and has a single portal of entry beneath; its interior arrangement is much like that of _Myrapetra scutellaris_.

{83}A very remarkable wasp's nest is preserved in the British Museum of Natural History; it is considered to be the work of _Montezumia dimidiata_ Sauss. an Eumenid wasp; it is a large mass of cells encircling the branch of a tree, which therefore projects somewhat after the manner of an axle through the middle: the cells are very numerous, and are quite as regular as those of the most perfect of the combs of bees: the mass is covered with a very thick layer of paper, the nest having somewhat the external appearance of half a cocoa-nut of twice the usual size.

[Illustration: Fig. 33—Section of nest of _Chartergus chartarius_. South America, _o_, Entrance. (After de Saussure.)]

_Apoica pallida_, a South American Insect, forms a nest in a somewhat similar manner to _Polistes_, but it is covered on its outer aspect by a beautiful paper skin, so that the nest looks somewhat like a toadstool of large size attached to the branch of a tree.

The nests of the Insects of the genus _Polybia_—which we have already mentioned as located by de Saussure in his unsatisfactory group Poecilocyttares—usually have somewhat the form and size of pears or apples suspended to twigs of trees or bushes; these little habitations consist of masses of cells, wrapped in wasp-paper, in which there are one or more orifices for ingress and egress. Smith says that the combs in the nest of _P. pygmaea_ are of the most exquisite construction, and that it is by no means an uncommon circumstance to find the outer envelope of the nest ornamented with patches of delicate hexagonal tracery. This nest is about the size of an orange.

We have already noticed the variety of nests formed by our British species of the genus _Vespa_; in other parts of the world the edifices formed by species of _Vespa_ attain a very large size. _V. crabroniformis_ in China, and _V. velutina_ in India, make nests several feet or even yards in length, inhabited by an enormous number of individuals; they are apparently constructed of a material like brittle paper, and are arranged much like the nests of our British hornet, _V. crabro_. _Vespa orientalis_ mixes a considerable quantity of earth with the paper it uses for its {84}constructive efforts. In the British Museum collection there is a nest said to be that of the Japanese hornet, _V. japonica_. This is completely covered by a paper envelope, and has apparently only a single small orifice for ingress and egress. In the same collection there is a nest from Bahia (believed to be that of a social wasp, though of what species is unknown), the outer wall of which is apparently formed entirely of earth, and is a quarter or half an inch thick: the comb inside appears also to be formed of clay, the whole forming an elaborate construction in pottery. One is tempted to believe it may prove to be the production of a social Eumenid.

HABITS OF SOCIAL WASPS.—We have already briefly noticed the way in which a colony of wasps is founded, but some further particulars as to the mode in which the society is increased and developed may be mentioned. The queen-wasp makes at first only a very small group of three or four incomplete cells; each cell is at first circular, or nearly so, and moreover is of smaller diameter than it will afterwards be. In each of the first three or four incomplete cells an egg is laid, and more cells are commenced; but as the eggs soon hatch and produce larvae that grow rapidly, the labours of the queen-wasp are chiefly directed to feeding the young. At first she supplies them with saccharine matter, which she procures from flowers or fruits, but soon gives them a stronger diet of insect meat. This is procured by chasing living Insects of various kinds. Some species of wasps prefer particular kinds of Insects, and the hornet is said to be very fond of the honey-bee, but as a rule Diptera are the prey selected. When an Insect has been secured, the hard and innutritious parts are bitten off, and the succulent parts, more especially the thorax which contains chiefly muscular tissue, are reduced to a pulp by means of the mandibles; this is offered to the larvae, which are said to stretch out their heads to the mother to receive the food, after the manner of nestling birds. When a larva is full grown it spins a cocoon in the cell and changes to a pupa. It is said by some entomologists that the queen-wasp closes the cell for the purpose of the larval metamorphosis; but this is contradicted by others, and is probably erroneous. In about a month, or a little less, from the time of deposition of the egg, the perfect Insect is ready for issue, and almost immediately after leaving its cell it assists in the work that is going on for the development of the society. The {85}Insects produced at this early period of the colony are exclusively workers, _i.e._ imperfect females. They relieve the queen of the task of supplying the larvae with food, and she henceforth remains within the nest, being, it is said, herself fed by her workers; the society now rapidly increases in numbers, and fresh combs are formed, the upper layer being always the oldest. About the month of August, cells of larger size than those that have previously been constructed are formed, and in these males and perfect females are produced; in a few weeks after this the colony languishes and becomes extinct. When it is no longer possible for the enfeebled wasps to carry out their tasks of feeding the brood, they drag the larvae out of the cells and destroy them. An uncertain number of queen-wasps seek protected nooks in which to pass the winter, and each of these queens may be the founder of a nest in the ensuing spring. It should be remarked that de Saussure states that all the intermediate grades between perfect and imperfect females exist, and Marchal's recent observations confirm this. There is in fact no line of demarcation between worker and queen in the wasps as there is in the honey-bee. Von Siebold long since drew attention to the existence of parthenogenesis in certain species of wasps, and it appears probable that it is of common occurrence.

Our knowledge of the social life of European wasps has recently been much increased by the observations of two French naturalists, P. Marchal and C. Janet. The latter has given an elaborate history of a nest of the hornet, showing the rate and variations of increase in numbers. His observations on this and other species indicate that warmth is of the utmost importance to wasps; the Insects themselves create a considerable amount of heat, so that the temperature of their abodes is much greater than that of the air. He considers that in Europe an elevated temperature is essential for the development of the individual,[43] and that the chief object of the various wrappers of paper with which the Insects surround their nests is to keep up this high temperature. These envelopes give a great deal of trouble to the Insects, for they have to be repeatedly {86}destroyed and reformed, as the combs they contain increase in size. Marchal's observations[44] relate chiefly to the production of the sexes and worker-forms, in the subterranean species, _Vespa germanica_ and _V. vulgaris_. The layers of comb include cells of two sizes. The upper layers, which are the first formed, consist of small cells only: the lower combs are constructed (at Paris) early in August, and consist of larger cells from which males and large females are reared. The males are, however, reared also in large numbers in the small cells. If the queen be removed, the workers become fertile, and produce parthenogenetically many eggs, but all of the male sex. He entertains no doubt that even when the queen is in full vigour the workers produce males if there is an abundant food supply.

The social wasps at present known number 500 or 600 species. _Polistes_ is a very extensive genus, and it has also a very wide geographical distribution; some of the species—and those found in widely-distant parts of the world—are remarkable on account of their excessive variation in colour, and it is worthy of note that the extreme forms have been more than once taken from the same nest.

Next to _Polistes_, _Vespa_ is the most numerous in species, about 150 being known, and it is to this genus that all our British social wasps belong. No Insects are better known in our islands than these wasps, owing to the great numbers of individuals that occur in certain seasons, as well as to their frequently entering our habitations and partaking of our food, and to the terror that is occasioned by their supposed ferocity and desire to sting. This last feature is a complete mistake; wasps never sting unless they are roused to do so by attacks, or by considerable interference with their work. The only real danger arises from the fact that a wasp may be occasionally taken into the mouth with fruit, or may be handled unawares. When they are flying about they are perfectly harmless unless attacked or irritated, and even if they settle on the person no danger of their stinging exists unless movement is made. Sichel correctly states that a person may station himself close to a wasp's nest and remain there without any risk at all, provided that he makes no movement; indeed, it is more than probable that if no movement, or if only gentle {87}movement, be made, the wasps are unaware of the presence of an intruder. It is, however, well ascertained that if they are molested at their work, more especially when they are actually engaged in the duties of the nest, they are then extremely vindictive, and follow for a considerable distance those who have irritated them. The East Indian _V. velutina_ is specially fierce when aroused, and is said by Horne to have followed a party through dense jungle for miles, and on some occasions to have stung animals, and even human beings, to death.

[Illustration: Fig. 34—_Ischnogaster mellyi_. Java. A, Female imago (the line at the side shows its length); B, nest, C, maxilla; D, labium; E, mandible (tip downwards). The nest is probably upside down, although shown here as by de Saussure.]

This vindictiveness is, however, only an exceptional mood due to some interference with the colony. Even the hornet, notwithstanding its threatening appearance, is harmless unless unduly provoked; its nests and their inhabitants can be kept in domesticity, exhibited to strangers, even moved from place to place, yet the hornets will not take offence if due gentleness be observed. It is said that wasps will rear the progeny of a neighbour in circumstances where this assistance is necessary. Hess has related a case in which a queen-hornet had commenced a nest, and was killed by an accident, leaving young brood in the comb {88}unprovided for: as a result many of the helpless grubs died, and others were in a state of starvation, when a strange queen-hornet appeared, associated itself with the comb, and, adopting the orphan brood, nourished them and brought them to their full size.

We have already alluded to the fact that, so far as external structure is concerned, there is no great difference between the social and the solitary wasps. Both, too, run through analogous series of forms and colours, and the genus _Ischnogaster_ (Fig. 34) seems to connect the two groups by both its structure and mode of life. The social habits are in many species only inferred, and with greater knowledge will probably prove fallacious as a guide to classification; indeed we have already said that in the genus _Vespa_—perhaps the most perfectly social of all the wasps—there is one species that has no worker, and that lives, it is supposed, as a parasite, in the nests of its congeners. For this species, _V. austriaca_, it has been proposed to create a separate genus, _Pseudovespa_, on account of this peculiarity of habit, although no structural character has been detected that could distinguish it. De Saussure has stated his conviction that workers do not exist in some of the exotic genera, so that it appears highly probable that with the progress of knowledge the present division between social and solitary wasps will prove untenable.

Remains of Insects referred to the genera _Polistes_ and _Vespa_ have been found in tertiary strata in various parts of Europe and in North America.

[Illustration: Fig. 35—_Masaris vespiformis_. A, male; B, female. Egypt. (After Schaum.)]

FAM. 3. MASARIDAE.

_Anterior wing with two complete sub-marginal cells. Antennae usually incrassate or clubbed at the extremity. Claws distinctly or obsoletely dentate._

This is a group of fifty or sixty species with but few genera, {89}and most of its components appear to be Insects of the greatest rarity. In their appearance the Insects of this Family differ considerably from the other Diploptera, and as the wings are only imperfectly, or not at all, plicate, it must be admitted that the systematic affinities of the group require reconsideration. The pronotal structure is, however, completely that of Diploptera. The typical form of the Family, _Masaris vespiformis_, though described a hundred years since, is a species of such extreme rarity, and its sexes are so different, that entomologists have only recently been able to agree about it. It has been found in Egypt and Algeria. The genera _Ceramius_, _Jugurthia_, _Quartenia_ and _Coelonites_ are also members of the Mediterranean fauna, while _Paragia_ is Australian, and _Trimeria_ South American. Several species of the genus _Masaris_ inhabit North America, and Cresson has recently described another Masarid genus from the same country, under the name of _Euparagia_.

The little that is known of their natural history is almost limited to an account given by Giraud of the habits of _Ceramius lusitanicus_, of which species he found a colony near Briançon. The Insect makes nests in the earth; they are entered by means of a chimney-like passage analogous to what is formed by certain _Odynerus_; the gallery when completed is about six centimetres long, and at its extremity is an earthen cell in which the larva lives; this is fed by the mother, who brings to it from time to time a supply of a paste, described as being somewhat like dried honey. The growth of the larva is believed to be rapid.

[Illustration: Fig. 36—Cells constructed by _Coelonites abbreviatus_. (After André.)]

Some fragmentary observations made by Lichtenstein on _Coelonites abbreviatus_ have also been recorded. This species, near Montpellier, constructs earthen cells; they are not, however, subterranean, but are placed side by side on the dry stems of plants (Fig. 36); these cells are stored with a material similar to that supplied by _Ceramius lusitanicus_ to its young.

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