HYMENOPTERA(the Piezata of Fabricius, Hautflüger or Aderflüger in German), an order of Insecta (so named from their wings being joined, as hereafter described) containing the insects commonly called bees, wasps,, ants, ichneumons, gall-flies, saw-flies, and others less known which have received no English names. The main characteristics of the order are these :—the possession of four wings, of which the anterior are always larger than the posterior, always of the same texture, and mostly with nervures arranged in regular patterns; a dense hard skin, smooth, shining, or very hairy; a mouth always provided with mandibles adapted for biting, though the other mouth parts may be so modified as to serve for mastication, or for the sucking, or rather lapping, of liquids. The female is provided with an anal instrument connected with oviposition, and sometimes serving for defence, in which case it is in communication with a poison gland. They undergo a regular transformation, and have larvae provided with legs on the thorax and abdomen, or on the former part only, or (as is more often the case) entirely footless.
The wings have few nervures, and may be even entirely devoid of them; when present they proceed from the base of the wing, or from the costa (the part which bounds the wing in front) towards the apex, which they may or may not reach. Connected with the lateral nervures are others (recurrent nervures) which unite them together, and form in this way regular cellules. The first two lateral nervures (those nearest the top) are the most important, and are called the “marginal” and “submarginal” respectively. The cellules which they form by means of the cross or recurrent nervures are called the “marginal” and “submarginal cellules.” Not unfrequently there is, towards the apical third of the costa, a thickened spot (considered by some to act as a counterpoise when the insect is flying) termed the “stigma” or “pterostigma.” It is not always present, however, and when present may be very small, or, as in Pachylosticα, Nexγ large and projecting. In a similar way the hind wing may contain lateral and cross nervures, but they are fewer in number and in importance, and may bè entirely absent, although present in the larger pair. The arrangement of the nervures in the Hymenoptera undergoes, in the various families, great diversity; and, what is of great importance in classification, their form, in the different families, and even genera, is, within certain limits, remarkably constant. On this account great attention has been paid to them; and each nervure and cellule has received a distinct name. The use of the nervures and cellules does not lead to the formation of artificial groups; for we find that the existence of a particular arrangement of the nervures in a hymenopterous insect denotes the presence of other characters. Each family indeed has its own form of wing, as will be seen from the accompanying figures. The relative value, however, of the neuration in classification is not always the same. It is of much greater importance, for instance, with saw-flies than with bees. The wings are usually shorter than the body, and may be so short as to be useless for flight; they may be even entirely absent. Apterous species are found in almost all the families. In most cases it is the females only which are thus deprived of the power of flight. But the opposite of this may exist; as, for instance, with a curious species of Chalcididoe which lives in'the nest of bees as a parasite. With ants, again, the neuters are always wingless; and the females lose their wings when they commence the formation of a colony. It is worthy of remark, too, that some Chαlci∙ didce and Oxyura, which are normally winged, occasionally appear in an apterous or semi-apterous condition. On the anterior margin of the hind wings are placed a number of very minute hooks, which fit into a thickened rim on the posterior margin of the front wings, so that the two become united, and strike the air as one whole. The wings are usually transparent, and, in certain arrangements of the light, are seen to be highly iridescent. Occasionally they are coloured in patches, or are entirely black or blue; in the latter case, they are not unfrequently of a thickish texture and have a metallic lustre, as, e.g., in Hylotoma. The smaller forms (Chalciclidoe and Oxyurd) have few or no nervures. Some of these have the wings deeply fringed; and Mymar anàFlabrinus have the wings as it were cleft and stalked; that is to say, there is a long, thin stalk projecting from the thorax for a certain distance; then it dilates into a number of deeply fringed branches (see fig. 5).
The head is seldom broader than the thorax. It is usually of a more or less globular shape, but may be much flattened and long. The compound eyes are placed along the sides, while the simple eyes, or ocelli, are arranged in a triangle on the vertex. Certain ants and Chalcididoe are blind. Others have eyes, but want the ocelli. The mouth organs are, except with bees, adapted solely for mastication or for prehension; while, in addition to performing these functions, wasps use them for building up or digging out their nests in the ground or wood. Some worker ants and other aculeates (especially males) have the mandibles enormously developed. Dlastophaga, an insect found in figs, has a curious mandible, remarkable, not in itself, but by having attached to it an appendage whose use is supposed to be to clean away the juice of the fig from the mouth. The maxilla and labium are provided with jointed palpi.
The number of joints in the maxillary palpi is usually five, but may be more or less than that; the labial palpi are two-to four-jointed. It is with bees that the mouth parts (and especially the ligula) have their greatest development and specialization. With them the various parts (except the mandibles) are elongated to form a sucking tube, by means of which they lap up the nectar of flowers.
The form of the antennae is very variable. They may have three (Hylotoma) to sixty joints (ichneumons); may be very long and thin as in ichneumons, or scarcely projecting beyond the head as in Perga ; of uniform thickness, or distinctly clavate as in Cimbeχ∙, bare, or very hairy. Then they often differ very much in the males. Lophyrus (Tenthre- dinidoe)oxLd many Chalcididoe have them pectinated in various degrees; they are deeply forked in Schizoceτa ; and many others have them covered with long hair, although they are quite bare in the other sex. In some families the number of joints varies very much, but most Aculeata have the same number, namely, 13 in the male and 12 in the female. These appendages serve as sense organs, especially for the discovery of food, and, in the male, for finding the female. At any rate an ichneumon (for instance) when searching for a larva in which to lay its eggs (and this has especially been noticed with those which oviposit in concealed larvae) keeps them in a state of continuous trembling motion, and males have also been observed to do the same when searching for the females.
The three divisions of the thorax—pro-, meso-, and metathorax—have pretty much the same relative proportions in all the families. The prothorax is small. The upper part is strongly articulated to the mesothorax, while the lower is freer; and it is by means of this lower part that the head is united to the thorax. The metathorax is very large, as might be expected, from its having to take such an important part in flight. As for the scutellum it varies more than any other portion of the thorax. Mostly it is flat, or at least only slightly raised above the mesonotum; but in the smaller groups (Oxyura, Chalcididoe, Cynipidoe) its form is sometimes very curious. In Aegilips (Cynipidoe) and Agriotypes (Ichneumonidoe) it is produced into a sharp more or less curved spine; in Eucoela it is cup-shaped, that is to say, it is raised up, and has the centre hollow. It undergoes, however, its greatest development with some Chalcididoe. In Chirocerus, for example, it is lengthened so much that it reaches the middle of the abdomen. The metathorax is never very large, nor does it exhibit any marked peculiarities.
The legs show the same manifold diversity in form that we found to exist with the other appendages. The basal parts—thecoxae and trochanters—are not usually of any size, except in the lower tribes, e.g., Chalcididoe. In classification the trochanters are of value, for we find with the Aculeata they are joined to the femora by a single joint, whereas in all the other Hymenoptera there are two joints. Hence the bees, wasps, &c., form the division Moηotrocha; and the ichneumons, saw-flies, &c., are denominated Ditrocha. Some Chalcididoe have the femora greatly thickened, and toothed on the under side j but as a rule it does not show any striking peculiarity unless it be with some male insects. As might be expected from their more intimate connexion with the habits of the insects, the tibiae and tarsi vary according to the uses they are put to, apart from locomotion. With bees (at least with the non-parasitie species) they are employed to carry the pollen necessary for the nourishment of the young; for this purpose they are provided with hairs, or the apex of the tibiae and base of the tarsi are flattened out to form a plate on which the pollen is stored for its easier and more economical conveyance to the hive. They are richly spined in the sand-wasps, and are thus useful to the animals in digging out the nests which they form in the earth. At the base of the tibiae are placed two spurs (calcaria), which, however, may be absent. Finally the tarsi are provided with plate-like processes termed patellae, which may be very largely developed, especially with males; and the front pair may terminate in large jointed raptorial claws, as is the case with Chelogynus {f)xyura).
The abdomen may be united to the metathorax in two ways: it may be joined to it by its entire width, or by a narrow pedicle only. In the former case the thorax and abdomen form as it were one whole, so that the body has the appearance of being composed of only two parts; whereas in the other section the three divisions, head, thorax, and abdomen, are clearly separated, or specialized. It is only the Siricidae and Tenthredinidae which have the abdomen united by the whole width. Thus the order becomes divided into two well-marked divisions, one represented by the Tenthredinidae (having the abdomen sessile) and the other by the Aculeata, Ichneumonidoe (having it appendiculated). The abdomen shows little variation in structure or form in the Tenthredinidae ; but does so to a large extent with the others. Usually more or less globular and rounded, and not of any great length compared to the head and thorax, it is often very much compressed and sabre-like, as in Ophion, or very long and thread-like as in Pelecinus∙, then it may be joined to the thorax in such a way as to be semi-sessile, or by a very long, thin, threadlike pedicle {Peloρosus, many Chalcididae, and Cynipidae). Between these two extremes there are all gradations, the form of the abdomen depending on the habits of the insect, upon its manner of self-defence or of oviposition. As regards the number of the segments, it varies. It is 8 with the Tenthredinidae and with the Siricidae, but in other groups it is less. Through one or other of the basal segments being greatly developed, and the terminal ones correspondingly reduced in size, some groups appear to have only 3 or 4 {Chrysididae). The Aculeata have always the same number, namely, 7 in the males and 6 in the females. Some bees {Coelioxys) and Chrysididae have the abdomen armed with spines or teeth at the apex.
The male and female organs are situated at the end of the abdomen. They are rarely conspicuous externally with the males; but in some females they are of great length, and may indeed exceed considerably the length of the body. However different in the various groups of Hymenoptera the organs connected with the laying of the eggs may be, they are fundamentally constructed on the same plan in all of them, no matter how different they may appear or how various the ways in which they may be used. A typical ovipositor in the Hymenoptera may be described as being composed of three bristle-like organs,—one placed above, and the others below. This upper bristle is channelled throughout, and has (when in use) the others pressed to it in such a way that the three together form a narrow tube, through which the egg passes. The two lower bristles are toothed at the lower end. These three parts are enclosed between a couple of two-jointed valves, situated at their base, which serve them as supports. Thus the ovipositor consists of five different parts. It exists under two forms. In the bees and wasps {Aculeata) it takes the form of a sting, or weapon of defence; and it is connected with a gland secreting a poison (the principal constituent being formic acid) which the insect injects by means of the sting into any thing that attacks it. Besides this defensive (or offensive) use to which it is put, it is employed by the sand-wasps to benumb the larvae and other insects or spiders with which they store their nests for the use of their young, in such a way that they remain to all intents and purposes lifeless, yet still keeping fresh, until such time as the wasp-larvae escape from the eggs and are ready to feed on them. In the rest of the order—with ichneumons, saw-flies, <kc.— it is not used as an instrument of defence (some ichneumons, indeed, will attempt to pierce the hand with it when caught, but they are never able to do any harm); it is simply an instrument for laying the eggs, and is not connected with a poison gland, or at any rate with a gland secreting a poison similar to that of a wasp. A poison gland exists, for instance, with saw-flies, but its purpose and also the manner of its use are different from what they are in the case of the aculeates. Its function is to act on the plant in which the eggs are laid,—either to raise galls in which the larvae will find food and shelter, or to prevent the hole made by the ovipositor for the reception of the egg from closing in on the egg, and thereby crushing it; for we find that eggs laid, for example, on leaves are not closely pressed by the substance of the leaf, but have a more or less open space surrounding them.
From the observations of Kraepelin on the development of the ovipositor, it seems clear that the grooved central bristle and the two basal sheaths arise in the larva from papillae situated on the under side of the ninth abdominal segment, while the two lateral (or rather lower) bristles have their origin in similar papillae on the eighth. It would appear also highly probable that the parts are true appendages of the abdominal segments, rather than modified portions of the body walls.
The ovipositor is either hidden (as is mostly the case) or may be exserted to a greater or less extent. Its length varies with the habits of the species; that is to say, the longer it is, the deeper, in wood, or in any other substance, does the larva, on which the ichneumon is a parasite, live. Species with long ovipositors occur in all the parasitic families, except the Oxyura and Chrysididae. With the last-mentioned family it is tubular. It is strangely modified with the saw-flies. With them it forms a veritable sawing apparatus (hence the name of these insects), being broad, plate-like, and toothed in various ways and degrees according to the habits of the insects; according as the eggs are laid in leaves or in bark it is slender and thin or broad and thick. In the pupa state Hymenoptera with long ovipositors have them curled up on, and closely pressed to, the back. It is a curious circumstance that this embryonic condition of the ovipositor is retained in the perfect state by a few forms, as, e.g., Leucaspis.
As remarked at the beginning of this article, the Hymenoptera go throtigh a regular metamorphosis—appearing in four distinct forms. The egg is generally longer than it is broad, and rounded at both ends. The skin is always thin, never sculptured, and rarely coloured; the only instance of colour in any of their eggs known to the writer being in those of certain saw-flies which are more or less greenish, and this colour may have been imbibed from the leaf. Many parasitic species (Ophion, Cynips, Myrnar) have pedunculated eggs,—eggs provided with a long pedicle or stalk, by means of which they are attached to the plant or insect, as the case may be. A Τryphon, for example, attaches her stalked eggs to the larva’s skin; it hangs by the stalk; and when the young tryphon-larva’s development in the egg is matured it leaves it by the lower end, and then proceeds to bore its way into the inside of its victim. A curious phenomenon has been observed to take place in hymenopterous eggs shortly after being laid; it is that they swell up (perhaps by imbibing moisture, although this cannot be the sole cause of the swelling) to double or more than double the size they were when laid. Trie number of eggs laid by a female varies of course with the species. Colonial species lay the greatest number; but with them the eggs are not laid all at once, as is the case with solitary species. Some social forms lay comparatively few eggs, while, on the other hand, many saw-flies and ichneumons must lay some hundreds. Solitary bees and wasps do not lay many; but it must be remembered that the storing of food and the building and digging of the nest are workf of labour and time.
The larvae are of two sorts. Those of species with a petiolated. abdomen are white, footless grubs, incapable of any extended motion; nor is this necessary, for they have not to seek their food, Which is provided for them by their mothers,—either collected and stored up for them in nests made by the female, as with bees and wasps, or by the eggs being placed in the bodies of other insects on which they live as parasites, or in galls upheaved on plants. It is, however, of interest to note that, While the larva after leaving the egg shows no trace of legs, yet they were present when it was in the egg. This shows clearly that the legs were lost through disuse. And this view is confirmed by the fact that the larvae of the lowest division of the Hymenoptera, those with a sessile abdomen, have jointed thoracic legs, and often abdominal legs as well, while they, for the most part, lead a free existence. In the lowest group of this division, the Siriddae, as well as in those Tenthredinidae most nearly allied to them, the larvae have only the thoracic or true legs. They live either boring in wood, as Sirex, or in stems of plants, as Ceρhus, or in leaves rolled together by silken threads, as Lyda. Except Lyda, Cephus, and Xyela, all the saw-fly larvae have the usual thoracic and a variable number of false or abdominal legs, which are in fact merely prolongations of the ventral surface of the body, as with many phytophagous Coleoptera ; nor have they anything like the claspers of lepidopterous caterpillars. With their similar habits and the presence of these ventral legs, saw-fly larvae have a considerable resemblance to the caterpillars of Lepidoptera, but they may be known from them in two ways,—by always having more than five pairs of ventral legs (eight in Cimbex, seven in Nematus, and six in some Hylotomides), and never having more than two ocelli—one on each side of the head—instead of six on each side as in Leρidoptera. As with lepidopterous caterpillars, green is the prevailing colour of saw-fly larvae. They agree with them, too, in their general habits: they live on the leaves of various plants, devouring them in different ways, roll down leaves, raise galls, and mine leaves. It is interesting to note further that, as with lepidopterous caterpillars, larvae which are innoxious and eaten by birds are either entirely green, or green with black, pink, or white stripes along the sides and back, while noxious larvae—those with bad smells or secretions which render them unpalatable to birds—have bright contrasting colours with irregular markings, tubercles, &c., and they feed exposed, so that they may be readily seen and avoided. Some hymenopterous larvae before becoming pupae moult a certain number of times. According to Packard, a Bombus casts off its skin ten times; Tenthredinidae do it five times; but many (all parasitic, and most aculeates) do not moult until they become pupae; nor do they empty the* contents of the stomach till then. The period during which a hymenopteron remains in the larva state is seldom long; it may be eight or nine days, or a month or two, but this depends on the season of the year; for many larvae, which have not been able to reach maturity in the autumn, remain in the same condition until the following spring, when they pupate. In order that this period may be passed in quietness, a cocoon is usually spun by the larva. For this purpose it is provided with a spinning apparatus, and a gland for secreting the silk required for the construction of the cocoon. With the Aculeata it is thin and almost transparent; it is of a firmer consistency with ichneumons, and is often coloured black, brown, or grey. Microgaster and other Bra- conidoe spin their cocoons in company, and often around the dead body of the larva which they have devoured. They may be placed together without any regularity, or closely pressed in regularly arranged rows like the cells in a hive. Some ichneumons suspend their cocoons from twigs, &c., by means of a silken thread. Generally the cocoon is single, but certain saw-flies {e.g., Cimbex) spin double ones,—a thin inner one (which may be separated from the outer one by a considerable space) placed inside an outer, harder, and more tenacious covering. A cocoon, however, is not always spun. Cynipidoe never spin one, nor apparently do Ghalcididae nor some ants, e.g., Myrmica. The empty skin of the caterpillar which they have devoured is utilized by some ichneumons instead of a cocoon; galls serve the same purpose with others; while Ernphytus and other Tenthredinidae bore into pithy stems, where they pass into pupae without any other protection. Finally, others make a cell in the earth for the same purpose.
The pupa resembles very closely the perfect insect, save that the wings are not developed, although visible as pad-like structures along the sides. The legs and antennae are laid along the front of the body, enclosed in thin pellicles. In certain Ghalcididae (Eulo-ρhus) the pupa is of that form called “coarceate”; that is to say, the entire body is enveloped in a case which conceals its form, and this case is hard and of some thickness, instead of being a mere thin transparent skin. When the insect leaves this pupal covering the latter retains its form intact. Most pupae are white. Manysaw-fly pupae are green, with orange spots on the abdomen. A few Braconidoe (Apanteles) have orange-coloured pupae.
In the pupa state Hymenoptera remain but a short time,—as a rule, not more than seven to ten days. They are not entirely quiescent in this condition, but have considerable power of motion, especially if exposed to the light, or disturbed in any way. As the insect gradually reaches maturity, the pupa becomes more or less black,—at first on the back of the thorax, then on the abdomen and limbs. When maturity is gained, the insect splits the pellicles which so closely envelop its body; the limbs are freed; the wings spread out and lose their flabby consistency; the nervures become hard and firm; the insect moves about, ejects from the anus a coloured liquid, and enters on its new mode of existence.
Hymenopterous insects procreate by the union of the two sexes. This takes place usually in the sunshine. Sometimes the connexion does not last more than a few seconds, and is not preceded by any preliminary courting. On the other hand many bees remain united for hours, and the genital parts of the male get torn and ruptured, so that it dies immediately after. Some species of Ghalcididae have been observed coquetting together for more than an hour before uniting. Generally copulation takes place on the ground; but a few forms pair on the wing. The male Anthophora, for instance, carries the female with him into the air for the marriage flight. This is the reason why the male Anthophora is larger than the female, instead of being smaller, as is usually the case.
While, as has been said, Hymenoptera reproduce by the union of the two sexes, yet parthenogenesis or virgin reproduction is of not uncommon occurrence, and has been observed in all the families whose development for more than one generation can be traced with sufficient facility and accuracy. We meet with this phenomenon under (broadly speaking) two or three phases. Many females, if they cannot get access to males, will readily lay eggs, which are fertile and give issue to larvae; but these larvae, when they reach maturity, yield invariably males. Any one can test this for himself with the too common gooseberry grub, Nematus ribesii. The same thing occurs with wasps, ants, and bees. With saw-flies, again, there are some species whose males are quite unknown, although the species have been caught and bred from the larvae in hundreds, e.g., Hriocampa ovata. Others have males, but they are extremely rare, e.g., Nematus gaUicola. It has been shown, too, that the species just mentioned and some others (Phyl-lotoma ηemorata, Poecilosoma pulveratum, <fcc.) with males unknown readily lay fertile eggs. The queen bee can lay eggs which will produce males or females, by opening or closing the spermatic sac, and letting the eggs come in contact or not with the spermatic fluid. In the former case females will be the result, in the latter males. Worker bees, wasps, and ants deposit eggs which produce, however, only males. A still more curious phenomenon in connexion with the reproduction of some gall-insects (Cynipidoe) requires to be mentioned. In early spring will be found on oak leaves and flowers soft, juicy, greenish, globular pea-shaped galls. Out of these come in summer the gallflies represented by both sexes. In the autumn (also on oak leaves) are found those curious flat brownish galls commonly called “oak spangles,” which by many are taken for fungi, and have indeed been described as such. These “spangle galls” retain very much the same form during the autumn and winter; then in March they swell up and become juicy, and a larva makes its appearance; this soon becomes a pupa and finally a fly, but only in one sex, the female. It was long supposed that these two insects had no relationship with each other, that they belonged in fact to two distinct genera, for not only did the galls differ, but the insects themselves differed in the form of the body, the wings, àc. But it has recently been shown by Dr Adler that the two are forms of the same species, that there is an alternation of a spring bisexual form, with an autumnal unisexual one.
A dimorphism of another kind exists among the social bees, wasps, and ants. An ordinary colony of these insects consists of three sorts of individuals. There is the large female which founded the colony; then there are the workers or neuters, undeveloped females on whom the work of the colony depends; and, lastly, there are the males. It is with ants that the workers are most profoundly modified. They are wingless, and there may be in a colony several sorts, each kind performing different duties, and having the body modified in accordance with the work it has to do. Those which act as soldiers (when a special kind is set apart for this work), for instance, have the mandibles enormously developed; another set may secrete honey for the benefit of the others, &c.
The Hymenoptera must be regarded as one of the most beneficial and useful to man of the insect orders. The produce of the hive bee—wax and honey—has been employed by man since the earliest ages, and forms an extensive article of commerce. The curious structures raised by Cynipidoe on the oaks of eastern Europe—galls—have long been used in the manufacture of ink. But, whatever the bee may have done in contributing to our luxuries, and the gall-fly in rendering easier the advance of knowledge, these are small benefits compared to the indirect advantages we derive from the labours of the parasitic species through the hιvoc they make among the insects which devour the produce of our fields and gardens, and too often destroy the labours of the farmer and gardener. When we remember that there are vast numbers of insects which destroy plants; that many of these are so minute and obscure in their mode of life as to escape ordinary observation, save when the injury is done; and that others appear in enormous numbers, —it becomes evident that an insect which causes the death of a single caterpillar does good service, since that caterpillar would have (if left undisturbed) given, in all probability, origin to an imago which might give birth to hundreds of others. It is this which the ichneumons do,— they destroy the larvae of plant-devouring insects. Another division of Hymenoptera does equally good service. It has been shown by modern researches that without the aid of bees many flowers would never yield seed. Many plants cannot fertilize themselves, so that if bees did not carry the pollen from one plant to another, and thus effect fertilization, no seed would be produced. The red clover, for instance, would never produce seed if it were not for the humble bees fertilizing it in their visits in search of honey. It must, however, be confessed that some Hymenσptera do very considerable damage to vegetation, especially saw-flies and ants. Of injurious saw-flies the most destructive are Eriocampa adumbrata, on fruit trees ; JVematus ribesii, which is so destructive to the gooseberry and red currant; Athalia spinarum, at one time so destructive to the turnip (probably when it first took to feeding on it); and Cephus, in the stems of corn. The damage done by ants in Europe is small; but in the tropics the leaf-cutting ants do enormous damage by cutting down the leaves of trees (especially cultivated ones), which they convey into their nests, where they are used (according to Belt) to rear fungi upon which the ants feed.
The Hymenoptera are almost exclusively dwellers on land, and are essentially sun-loving insects. Two or three only live an aquatic or quasi-aquatic mode of life. Sir John Lubbock discovered two minute species of Oxyura (JPoly-ηema) which descend into the water for the purpose of depositing their eggs in the eggs of aquatic insects. They use the wings as oars to swim in the water, and can remain in it for two hours. An ichneumon (Agriotypes) has long been known to live as a parasite in the bodies of caddisworms; and it has been observed to go down into the water to find the worms, which are said, when infested by the ichneumons, to anchor themselves by means of a silken thread.
Many Hymenoptera give origin to sounds. The humming of bees is one of the most familiar and delightful of country sounds. It is not yet quite clearly understood how it is caused, but there is evidence enough to show that the buzzing originates by the air impinging against the lips of the metathoracic and abdominal stigmas; although it is possible, too, that the rapid vibration of the wings (224 per second with the Bombus muscorum and 440 with the honey bee) may also have something to do with the production of sound, for a bee can give out differently pitched notes according to its mood, as it is pleased or angry. Besides the buzzing sounds, a few other species chirp by means of the abdominal segments. Mutilla stridulates by drawing in and out the raised striated surface of the third under the edge of the elongated second segment. The workers of Myrmica stridulate in pretty much the same way.
The internal anatomy of the Hymenoptera presents some interesting features. Their organs of secretion are numerous. The poison is secreted in two long ramose tubes; and from them it goes into a sac situated near the base of the sting. Wax is made in some of the abdominal segments. The salivary glands in the hive bee (worker) are very large and complicated. They are three in number, two (an upper and a lower) placed in the head, and the other in the front region of the thorax. Each gland is different, and has excretory ducts of its own. In the queen bee these are not nearly so much developed as in the worker, and they are even less in the drones. Many saw-fly larvae secrete fluids for purposes of defence. Some species of Tenthredo secrete a blackish liquid, which they eject from the mouth; Perga throws out a gummy matter from the same orifice, and Cimbex an acid liquid from lateral pores. Then there are the silk-secreting glands which most larvae possess. The urinary vessels are always present, and may be as many as 150. According to Von Siebold, the aculeates have a long intestine and a stomach with many convolutions, while they are short in the terebrant forms. The tracheae are well developed. Many dilatations are given off from the main stems, a pair at the base of the abdomen being exceptionally large. In connexion with the female organs of generation, it is worthy of remark that sebaceous glands and a copulatory pouch are absent in the Aculeata, although present in the other section. The ovaries are two in number, and consist of a number (it may be as many as a hundred) of distinct many-chambered tubes. Each tube in Athalia, for instance, contains 7 eggs, and, as there are 18 of such tubes in each ovary, there will be thus 250 eggs in all. In Platygaster the ovary is of a very exceptional nature, inasmuch as the egg tube is a close sac, so that it is burst when the egg is laid.
The most noteworthy and exceptional features in the developmental history of the Hymenoptera are those shown by some very minute species of Oxyura, which live in the bodies of Diρtera (Cecidomyia), and in the eggs of beetles and dragon-flies. After the eggs of Platygaster have undergone segmentation, and the embryo has been formed, there leaves the egg a larva of a very unusual form. It is broad and rounded at the head, but contracted towards the tail, which terminates in four spined, bristle-like appendages, so that the larva has a considerable resemblance to a copepod. It is provided with a mouth and hook-like mandibles, by the aid of which it anchors itself inside the body of its host (the larva of a Cecidomyia); there are a rudimentary stomach and antennae, but no trace of nerves, tracheae, or organs of circulation. Soon it changes its form: the tail with its bristles is thrown off; it becomes shaped somewhat like a hen’s egg; the nervous, circulatory, and reproductive organs become visible, while the alimentary organs show an advance in structure. This second larva is succeeded by a third, which differs from it in being longer and thinner, while the various organs have reached a further stage of advancement in complexity of structure. The after course of its development does not differ from that of other Hymenoptera. Polynema and Hymar (eggparasites) go through somewhat similar changes in their early embryonic life.
Classification.— As regards the classification of the Hymenoptera, the order divides itself naturally into two great divisions, as has been already indicated. The Aculeata form a division distinguished alike by the form of the sting, with its connected poison-bag, and by the trochanter being joined to the femur by a single joint. The other division (that usually called Terebrantia or Ditrocha) has a double joint to the trochanter, and the ovipositor is never used as a weapon of offence.
The Ditrocha are again divided into two sections, well distinguished by the form of the abdomen, by the larva, and by habits: the one (the Securifera) has the abdomen sessile, the larvae have legs, and they are phytophagous; while the other (the Sρiculifera) has the abdomen petiolated, the larvae are apodal, and they are (except part of the Cynipidae) animal feeders. The Securifera are further distinguished from all others by the form of the ovipositor, which forms either a short “saw,” as in the Tenthredinidoe, or a stout exserted “borer,” as in the Siricidae ; and they have another peculiarity in having at the bottom of the anterior wing a cellule, termed the “lanceolate cellule” (see fig. 1, above), which is found in no other family, and is of great use in classification. The Securifera embraces the families Tenthredinidoe and Siricidae (by some Cephus is made into a third family, while by others it is placed among the Tenthredinidoe, owing to its agreeing with the saw-flies in the form of the thorax and ovipositor, and by others with the Siricidae, because it has only one spine in the anterior leg, while the saw-flies have two). The species of Siricidae are few in number, and have a very wide distribution. They are larger than any Tenthredinidoe, and are indeed among the giants of the order. All live in wood, especially in Coniferoe, and have occasionally done great damage to the forests in Germany. As they are easily imported along with timber, they very often make their appearance in out-of-the-way places and frighten ignorant people, although, of course, they are perfectly harmless.
The Spiculifera contain the families Cynipidae, Chalcididoe, Broc- totrypidae, Evanidoe, Braconidae, and Ichneumonidae.
The Cynipidae, or gall-flies, are small insects, rarely exceeding two lines in length. The antennae are straight, inserted in the middle of the face; the joints are variously shaped, and do not exceed 16 in number. The thorax is large; the scutellum always forms a conspicuous object, and its form is very varied. The abdomen is much compressed, especially with the males; curled up over the apical segments is the long thin bristle-like ovipositor. A few species are apterous. There is always a radial cellule in the anterior wing, but few nervures and there is never a stigma. What distinguishes the Cynipidae more especially is their habit of raising galls on plants to serve as food and lodgings for their young. These galls have the most diversified shapes, and are raised on all parts of a plant—the buds, leaves, roots, flowers, and fruit all being used by the gall insects. A gall may serve to shelter a solitary larva, or it may be so large as to contain many hundreds. The oak is the principal tree used by the Cynipidae ; next is the rose, upon which is found the well-known “bedeguar gall” of Rhodites rosae, once used medicinally; the maple, poppy, bramble, hawkweed, and some other plants have likewise their galls. All Cynipidae, however, are not gall-makers. One group deposit their eggs in the galls raised by the true gall-makers, when they are soft and young, and the larva of the cuckoo-fly lives on the gall at the expense of the legitimate owner, which is killed by the more energetic intruder. Another group contains pure animal feeders, parasites which live at the expense of other insects (especially plant lice).
Closely allied to the Cynipidae is the family Chalcididoe, an immense tribe of very minute insects with brilliant metallic green bodies. Their wings have few nervures, and they never form closed cellules, but a stigma is always present. The antennae are always elbowed; they have never more than 13 joints, and may have as few as 6. With the males they are sometimes flabellate, or covered with tufts of hair. Generally the ovipositor is short and concealed, but it may be exserted and much longer than the entire body. In either case it issues from the lower side of the belly. Apterous and semi-apterous species are not uncommon. In habits the Chalcididoe are very diversified. They are parasites on insects of all orders and in all stages. While no definite line can be drawn, yet particular groups in the mass confine their attacks to certain families of insects. Thus Leucaspis and Chalcis are attached to bees and other nestbuilding aculeates, the long-tailed Torymides to oak and other galls, the Encrytides to Homoptera (Coccus especially). Species of Isosoma appear to be herbivorous, and one in America is destructive to corn, by raising gall-like structures at the joints and thus causing the plant to wither. Giraud has likewise described Isosoma to be a vegetable feeder, at any rate during a considerable portion of its life, as well as another species (Aulogymnus aceris) which lives in galls on the maple. Those curious forms, Sycophaga and Blastophaga, which live in figs, appear undoubtedly to feed on their seeds.
The species of Proctotrypidae (called also Oxyura), unlike those of the Chalcididoe, are dull-coloured insects, usually entirely black, or at best relieved by brown or red. They are distinguished from the last family by the non-elbowed antennae, which are 8- to 13- jointed. The wings in the smaller forms may be without nervures, while in the higher they are much more developed than in the Chalcididae. The edges of the wings are deeply fringed with some species; and other species have dense patches of hair on the thorax and abdomen. One group bears raptorial claws on the front tarsi; and, in connexion with this structure, it is worthy of notice that the late A. H. Haliday observed one species to kill and deposit in an empty straw a caterpillar, apparently for the purpose of laying its eggs in it; so that in habits it approximates to the fossorial Hymenoptera, which some of them undoubtedly do in structure. The Oxyura are parasites. Some are attached to gall insects, others to aphides, while Diptera and eggs of insects of all orders afford nourishment to many.
The insects usually called “ichneumons” belong to two families — the Ichneumonidae and Braconidae. Both are readily distinguished from the families already mentioned by the wings being well provided with nervures, which form regular cellules, by the greater number of joints in the antennae, and generally by their much greater size. The only radical distinctions between the groups are that the Ichneumonidae have two recurrent nervures, and a little joint in front of the second antennal joint, whereas this is absent in the Braconidae, which have besides only one recurrent nervure. In habits there is no broad distinction between them. They are parasites on insects of all orders. The Evanidoe are a small and somewhat heterogeneous assemblage of insects, which do not agree very well in their structure; but the typical species may be known by the abdomen being inserted in the middle or above the middle of the metathorax. As far as is known the family are parasitic on cockroaches, and appear to be not very numerous in species.
In some respects the Ghrysididae are intermediate between the Aculeata and the Terebrantia, for they have the single-jointed trochanter of the former, while in the structure of the ovipositor, in having the antennae 13-jointed in both sexes, as well as in habit, they agree with the latter. They are exceedingly brilliant insects; their bodies are metallic, with shining green, purple, or golden hues. The abdomen hangs as it were from the thorax, and is somewhat concave on the under side. It can be bent under the thorax, so that the insect can roll itself up into a ball, which is its way of protecting itself when attacked—its hard metallic coat of mail being impregnable against the mandibles of other insects. These insects differ from other terebrant Hymenoptera in the structure of the abdomen, for it has never more than four segments visible in the female and five in the male, while the ichneumons have always more. The terminal segments form a tube, which is used in oviposition. In habits the Ghrysididae do not differ from the ichneumons, being parasites. They prey principally on bees and wasps, whose nests they enter when the owners are absent, and should they be discovered their hard skin saves them from serious injury. Indeed the only portions of their bodies which can be mutilated are the wings. St Fargeau observed a bee do this to a chrysis; she bit off the four wings, but did not thereby save her young, for as soon as the bee left, the now wingless parasite crawled into the nest and laid her eggs therein.
As has been stated, the Aculeata are distinguished from all other Hymenoptera by having a sting, a single-jointed trochanter, and the antennae with 12 joints in the female and 13 in the male. They differ, too, in habits from the Terebrantia, for, although many of them are parasites, their parasitism is unlike that of the ichneumons. Parasitic Aculeata earn their bread differently: they enter the nests of other aculeate species and lay their eggs in the food stored up there for the benefit of the young of the builder, which are starved or destroyed by the more vigorous larva of the parasite. In order to carry out their ends with greater ease, some parasites mimic the forms of the species upon which they prey. Thus Apathus rupestris is coloured exactly like Bombus lapidarius, its host. On the other hand the species of Nrnnada, an extensive genus of parasitic bees, do not resemble in the least the bees on which they prey; they have instead gaudily coloured, hairless bodies. One of the most interesting chapters in the history of the Aculeata is their nest building. The nests are built in all sorts of places and of all kinds of materials.
Many, like Andrena, dig in light soils a burrow, consisting of a narrow passage going down some inches, and having at each side of it at intervals cells in which the food is stored. Wood is used by others to form somewhat similar cells, which may be lined with pieces of leaves or flowers. The stems of brambles are utilized by a large number of species of bees and fossorial Hymenoptera. Osmia uses empty shells for its habitation. Then others build up nests. Chalicodoma and other bees, with many wasps, construct cells by cementing together bits of mud and clay. Social wasps form their large nests of paper made of masticated wood; humble bees and the hive bee do so by a secretion called wax. Some ants build up from the ground, of leaves, &c., nests shaped like a hay-stack, which in size they may almost equal. An Indian species builds, at the ends of branches of trees, large nests of dead and living leaves matted together with a white web. Finally, the thorns of Acacia are hollowed out by others to serve as a residence.
The Aculeata may be divided into five families—the Formiddae, or ants, Mutillidae (commonly called “solitary ants”), Fossores (sand-ιvasps, &c.), Diploptera, or true wasps, and Anthophila, or bees. The ants are, as a rule, social insects, and their workers differ from those of wasps and bees in being always wingless. What morphologically more especially distinguishes ants from other aculeates is the structure of the abdomen, which at the base (on the peduncle or petiole) is provided either with a flattened plate-like projection or with two nodes. · In the former case, there is, as in Formica, only a rudimentary sting, while in the latter there is an efficient one, as in Myrmica ; but there are exceptions to both rules. A few ants are solitary and. parasitic in habits, and in this case the female is wingless. Closely allied to the ants are the Mutillidae (by some authors the two are placed in one group, Heterogena), which, however, differ from them in being solitary, in having neither a scale nor node, while the tibiae are spined, and the tarsi ciliated. It is only the males which are winged, and they have the abdomen spined and curved at the apex. They are brightly coloured insects, and are very numerous in species. So far as is known they are parasites on humble bees. The group of Fossores is a very extensive one. Their habits are very interesting and varied even in the same genus. They are carnivorous, storing up (after having benumbed but not killed) caterpillars, beetles, flies, aphides, &c., in cells formed or dug out of wood or of bramble stems, in the ground, or built up of mud or sand. Some build no nests, and store up no food for their young, but live, cuckoo fashion, on other Fossores or bees. In general structure the Diploptera do not differ essentially from the Fossores ; but they may be readily known from them by the wings being folded longitudinally in repose, while the eyes are reniform and reach to or near to the base of the mandibles. They differ too from the Fossores in some of them being social, as is the case with Polistes and Vespa. In habits the solitary wasps agree more or less with the Fossores. While the above-mentioned tribes are carnivorous, the bees, on the other hand,∙are entirely vegetable feeders, living on the pollen or nectar of flowers. As might be expected, we find with them certain peculiarities of structure in connexion with their habits. The great business of a bee is the storing up of food, for its own use or (and more especially) for that of its young. To do this to the best advantage certain parts of the body are adapted for the carrying home of pollen. This is done more especially on the legs. The basal joint of the tarsus is, for this purpose, flattened and compressed, and covered (at least on the inner side) with hair. This then, is a character which distinguishes them from all other aculeates. The least specialized bees carry home the pollen loose, but Apis mixes it into a paste in the field. To serve the same end the mouth parts are profoundly modified for the lapping of nectar, hlany bees are parasites on other bees. These want the pollen collecting apparatus, and many of them have bright-coloured hairless bodies, as already remarked.
The earliest Hymenoptera known belong to the upper Oolitic formation; but, as they are Apidae, it is certain that the order must have appeared much earlier in time than that. At the present day, representatives of the order are found in all parts of the world, even as far north as 78° to 83° N. lat., where Bombi and ichneumons were found by the naturalists attached to the Arctic expedition of 1875-76. Many genera in all the families have a very wide distribution, e.g., Ophion and Pimpla among the ichneumons, Ody-nenιs with the wasps, Megachile with bees. Humble bees and saw-flies are characteristic of temperate, if not northern, latitudes; Mutilla of warm regions, although it also appears in arctic regions. Vespa is rΑθxe limited in its range than the solitary wasps (Odynerus, &c.), being absent from Africa, Australia, and South America. Many individual species have a very extensive range. This has been brought about in some cases by the aid of man. In this way many pests have been carried over the globe, e.g., Nematus ribesii, the gooseberry grub, which is now spreading over the American gardens; Eriocampa adumbrata, the slug worm of British fπιit trees, has reached New Zealand; while, among ants, the house ant of Madeira (Pheidole pusilla) is now cosmopolitan. Many species are common to the Palaearctic and Nearctic regions, e.g., Megachile centuncularis, Vespa vulgaris, Hemichroa rufa. Others have a wider geographical range. The ant Solenopsis geminata, for instance, is found in India, the Eastern Archipelago, South America, and the Hawaiian Islands. Hylotoma pagana, again, occurs in the Southern States of America, and all over Europe, ana extends to India and Japan.
There being no complete list of Hymenoptera, it is not easy to give the number of described species, but probably it is not much over 17,000. The actual number, however, must be very much greater; probably it will be found to reach 70,000 or 80,000; for in those countries where anything like the same attention has been paid to them as to beetles they are nearly as numerous; and in no country have they received so much attention as Coleoptera. As regards the number of British species, there are recorded in the catalogues published by the Entomological Society of London, in 1871-2, 378 Aculeata, 1654 Ichneumonidee and Braconidae, and 325' 0xyura; while 325 saw-flies were catalogued in 1878—in all about 2700. Besides these there are about 150 Cynipidoe, and upwards of 1200 Chalcididae have been described by Francis Walker; but that number may safely be reduced to 600 or 700.
Bibliography.— I. Systematic. —westwood, An Introduction to the Modern Classification of Insects, 1840; Lepe)letier de Saint Fargeau and Brullé, Histoire Naturelle des Insectes Hyménoptères, 1840; Curtis, British Entomology ; Stephens, Illustrations of British Entomology, vol. vii. and Supplement, 1835; Fabricius, Systema Piezatorum, 1804; Costa, Fauna del regno di Napoli, 1861; Dahlbom, Hymenoptera Europoea proecipue borealia, 1843-1845; C. G. Thomson, Hymenoptera Scandinarice, 1872 et seq.∙, Jurine, Nouvelle méthode de classer les Hyménoptères, 1807; Kirby, Monographia apum Angliae, 1802; Mayr, Die Europäische Formiciden. 1861; Shuckard, Essay on the Indigenous Fossorial Hymenoptera, 1837; Smith, Catalogues of Hymenopterous Insects in the Collection of the British Museum, 1853 et seq.∙, Saussure, Monographie des Guêpes sociales, 1853. and Mon. des Guêpes solitaires, 1852; Kirchner, Catalogus Hymen. Europae, 1867; Förster, Hymenopterologische Studien, 1856; Gravenhorst, lchneumonologia Europoea, 1829; Haliday, “An Essay on the Classification of the Parasitic Hymenoptera of Great Britain,” in Entomol. Mag., 1833 et seq.∙, Hartig, Die Familien der Blattwespen und Holzwespen, 1837; Holmgren, Monographia Tryphonidum Suecioe, 1856; Id., Mon. Ophionidum Suecioe, 1861; Id., Mon. Pimpliarum Suecioe, 1860; Id., Ichneum. Suecica, 1871; Klug, Mongr. Siricum Germanice, 1803; “Die Blattwespen nach ihren Gattungen, <fcc.,” in Mag. der Gesellschaft Naturf. Freunde zu Berlin, 1807; Ratzburg, Die Ichneumonen der Forstinsecten, 1844-1852; wesmae), Monographie des Braconides de Belgique. See also many papers by westwood and Smith in Transactions of Linnean and Entomological Societies of London·, by Mayr and Giraud, on Chalcididae and Cynipidoe, in Verh. d. zool.-bot. Vereins in Wien ; by Förster in the same Transactions and in Verb, des naturhist. Vereins d. Preussischen Rheinlande u. Westphalens ; by Hartig, on Cynipidoe in Geιτnar's Zeit. f. Ent.·, as well as papers by various authors in the Stettiner Entom. Zeitung, the Berliner Ent. Zeitschrift, the Annales de la Société Entom. de France, <fcc.—II. Anatomical. —Dufour, Recherches sur Vanatomie des Hyménoptères, <fcc., Paris, 1841; Ganin, “Ueber der Embryonalhülle der Hymen, u. Lepidopt." Mène, de ΓAcad. de St Petersbourg, 1869; Biitschli, “Zur Entwickelungsgeschichte der Biene,” Zeitschr. wiss. Zool., xx.; Ganin, “Beiträge zur Erkenntniss der Entwick. der Insekten," Zeitschr. wiss. Zool., 1869; Kraepelin, “Untersuch, über d. Bau, <fcc., des Stachels der bienenartigen Thiere,” Zeitschr. wiss. Zool., 1873; Lacaze-Duthiers, “Mémoire sur l’appareil genital femelle des Hyménop.," An. des Sc. Nat., 1849; Newport, “Prize Essay on Athalia Spinarum," and various Memoirs on Chalcididae, <fcc., in Phil. Trails., 1852-53; Wolff, Das Riechorgan d. Biene u. Beschr. d. Pespirationswerkes d. Hymenop., 1875; Siebold, Wahre Parthenogenesis b. Schmetterlingen u. Bienen, 1856; Beitr. z. Parthenogenesis d. Arthropoden, 1871. (Ρ. CA.)
