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HYMENOPTERA (Gr. b$v, a membrane, and irrepov, a wing) , a term used in zoological classification for one of the most important orders of the class Hexapoda (q.v.). The order was founded by Linnaeus (Systerna Yaturae, 1735), and is still recognized by After C. L. Marian, Bur. Ent. Bull. .3, N.S., U.S. Dept. Agric. Flo. 1.A, Front of head of Sawfly (Pachynentatus) ; a, labrum; b, clypeus; c, vertex; d, d, antennal cavities. C and I), Mandibles. E, First maxilla; a, cardo; h, stipes; c, galea; d, lacinia; e, palp. B, Second maxillae (Labium); a, mentum; b, ligula (between the two galeae) ; c, c, palps. Magnified. all naturalists in the sense proposed by him, to include the sawflies, gall-flies, ichneumon-flies and their allies, ants, wasps and bees. The relationship of the Hymenoptera to other orders of insects is discussed in the article HEXAPODA, but it may be men- tioned here that in structure the highest members of the order are remarkably special- ized, and that in the perfection of their in- stincts they stand at the head of all insects and indeed of all inver- tebrate animals. About 3 o,000speciesof Hymen- optera are now known. Characters.In all Hymenoptera the man- dibles (fig. 1, C, D) are well developed, being adapted, as in the more lowly winged inoects,such as the Orthoptera, for biting. The more general- ized Hymenoptera have the second maxillae but slightly modified, their inner lobes being fused to form a ligula (fig. 1, B, b). I n the higher families this structure becomes elongated (fig. 2, g) so as to form an elaborate sucking-organ or " tongue." These insects are able, therefore, to bite as well as to suck, whereas most insects which have acquired the power of suction have lost that of biting. Both fore- and hind- wings are usually present, both pairs being membranous, the hind- wiugs small and not folded when at rest, each provided along the costa with a row of curved hooks which catch on to a fold along the dorsum of the adjacent fore-wing during flight. A large number of Hymenoptera are, however, entirely winglessat least as regards one sex or form of the species. One of the most remarkable features is the close union of the foremost abdominal segment (fig. 3, i.) with the metathorax, of which it often seems to form a part, the apparent first abdominal segment being, in such case, really the second (fig. 3, ii.). The true first segment, which undergoes a more or less complete fusion with the thorax is known as the " median segment" or propodeum. In female Hymenoptera the typical insectan ovipositor with its three pairs of processes is well developed, and in the higher families this organ becomes functional as a sting (fig. 5)used for offence and defence. As regards their life history, all Hymenoptera undergo a " complete " metamorphosis. The larva is soft-skinned (eruciform), being either a caterpillar (fig. 6, b) or a leg-less grub (fig. 7, a), and the pupa is free (fig. 7, c), i.e. with the append-ages not fixed to the body, as is the case in the pupa of most moths.Structure.The head of a hymenopterous insect bears three simple eyes (ocelli) on the front and vertex in addition to the large compound at 1. Tenthredinidae (Hylotoma) 2. Cynipidae (Cynips). 1, marginal; z, appendicu- 3. Chalcididae (Perilampus). lat.; 3, 4, 5, 6, radial or sub- 4. Proctotrypidae (Codrus). marginal; 7, 8, q, median or 5. Mymaridae (Mymar). discoidal; 1o, sub-costal; 6. Braconidae (Bracon). II, 12, cubital or branchial; 7. Ichneumonidae (Trogus). and 13, anal or lanceolate 8. Chrysididae (Cleptes). cellules; a, b, c, submarginal 9. Formicidae (Formica). nervures; d, basal nervures; io. Vespidae (Vespa). e, f, recurrent nervures; st, 11. Apidae (Apathus). stigma; co, costa. eyes. The feelers are generally simple in type, rarely showing serrations or prominent appendages; but one or two basal segments are frequently differentiated to form an elongate " scape," the remaining segmentscarried at an elbowed angle to the scapemaking up the " flagellum "; the segments of the flagellum, often bear omplex sensory organs. The general characters of the laws have been mentioned above, and in detail there is great variation in these organs among the different families. "The sucking tongue of the Hymenoptera has often been compared with the hypopharynx of other insects. According to D. Sharp
thorax the pronotum and prosternum are closely associated with the mesothorax, but the pleura of the prothorax are usually shifted far forwards, so that the forelegs are inserted just behind the head. A pair of small platesthe tegulae are very generally present at the bases of the fore-wings. The union of the first abdominal segment with the metathorax has been1. 0o Z 9 6 8 10 After C. Janet, Mem. Soc. Zool. France (r8y8). Fig. 3.Median section through mid-body of female Red Ant (Myrmica rubra). H, Head; 1, 2, 3, the thoracic segments; i., ii., the first and second abdominal segments; i., being the propodeum. already mentioned. The second (so-called " first ") abdominal segment is often very constricted, forming the " waist " so characteristic of wasps and ants for example. The constriction of this segment and its very perfect articulation with the propodeum give great mobility to the abdomen, so that the ovipositor or sting can be used with the greatest possible accuracy and effect. Mention has already been made of the series of curved hooks along the costa of the hind-wing; by means of this arrangement the two wings of a side are firmly joined together during flight, which thus becomes particularly accurate. The wings in the Hymenoptera show a marked reduction in the number of nervures as compared with more primitive insects. The main median nervure, and usually also the sub-costal become united with the radial, while the branches of radial, median and cubital nervures pursuing a transverse or re-current course across the wing, divide its area into a number of areolets or " cells," that are of importance in classification. Among many of the smaller Hymenoptera we find that the wings are almost destitute of nervures. In the hind-wingson account of their reduced sizethe nervures are even more reduced than in the fore-wings. The legs of Hymenoptera are of the typical insectan form, and the foot is usually composed of five segments. In many families the trochanter appears to be represented by two small segments, there being thus an extra joint in the leg. It is almost certain that the distal of these two segments really belongs to the thigh, but the ordinary nomenclature will be used in the present article, as this character is of great importance in discriminating families, and the two segments in question are referred to the trochanter by most systematic writers. The typical insectan ovipositor, so well developed among the Hymenoptera, consists of three pairs of processes (gonapophyses) two of which belong to the ninth abdominal segment and one to After C. Janet, Aiguillon de la Myrmica rubsa (Paris, ISO). the eighth. The latter are the cutting or piercing stylets (fig. 5, A) of the ovipositor, while the two outer processes of the ninth segment are modified into sheaths or feelers (fig. 5, C) and the two inner processes form a guide (fig. 5, B) on which the stylets work, tongues or rails on the " guide " fitting accurately into longitudinal grooves on the stylet. In the different families of the Hymenoptera, there are various modifications of the ovipositor, in accord with the habits of the insects and the purposes to which the organ is put. The sting of wasps, ants and bees is a modified ovipositor and is used for egg-laying by the fertile females, as well as for defence. Most male Hymenoptera have processes which form claspers or genital armature. These processes are not altogether homologous with those of the ovipositor, being formed by inner and outer lobes of a pair of structures on the ninth abdominal segment. Many points of interest
In the female, each ovary consists of a large number of ovarian tubes, in which swollen chambers containing the egg-cells alternate with smaller chambers enclosing nutrient material. In connexion with the ovipositor are two poison-glands, one acid and the other alkaline in its secretion. The acid gland consists of one, two or more tubes, with a cellular coat of several layers, opening into areservoir whence the duct leads to the exterior. The alkaline gland is an irregular tube with a single cellular layer, its duct opening alongside that of the acid reservoir. These glands are most strongly developed when the ovipositor is modified into a sting. Development.Parthenogenesis is of normal occurrence in the life-cycle of many Hymenoptera. There are species of gall-fly in which males are unknown, the unfertilized eggs always developing into females. On the other hand, in certain saw-flies and among the higher families, the unfertilized eggs, capable of development, usually give rise to male insects (see BEE). The larvae of most saw-flies feeding on the leaves of plants are caterpillars (fig. 6, b) with numerous abdominal pro-legs, but in most families of Hymenoptera the egg is laid in such a situation that an abundant food-supply is assured without exertion on the part of the larva, which is consequently a legless grub, usually white in colour, and with soft flexible cuticle (fig. 7, a). The organs and instincts for egg-laying and food-providing are perhaps the most remarkable features in the economy of the Hymenoptera. Gall-fly grubs are provided with vegetable food through the eggs being laid by the mother insect within plant tissues. The ichneumon pierces the body of a caterpillar and lays her eggs where the grubs will find abundant animal food. A digging-wasp hunts for insect prey and buries it with the egg, while a true wasp feeds her brood with captured insects, as a bird her fledglings. Bees store honey and pollen to serve as food for their young. Thus we. find throughout the order a degree of care for offspring unreached by other insects, and this family-life has, in the best known of the Hymenopteraants, wasps and beesdeveloped into an elaborate social organization. Social Life.The development of a true insect society among the Hymenoptera is dependent on a differentiation among the females between individuals with well-developed ovaries (" queens ") whose special function is reproduction; and individuals with reduced or aborted ovaries (" workers ") whose duty is to build the nest, to gather food and to tend and feed the larvae. Among the wasps the workers may only differ from the queens in size, and individuals intermediate between the two forms of female may be met with. Further, the queen wasp, and also the queen humble-bee, commences unaided the work of building and founding a new nest, being afterwards helped by her daughters (the workers) when these have been developed. In the hive-bee and among ants, on the other hand, there are constant structural distinctions between queen and worker, and the function of the queen bee in a hive is confined to egg-laying, the labour of the community being entirely done by the workers. Many ants possess several different forms of worker, adapted for special duties. Details of this fascinating subject are given in the special articles ANT, BEE and WASP (q.v.). Habits and Distribution.Reference has been already made to the various methods of feeding practised by Hymenoptera in the larval stage, and the care taken of or for the young through-out the order leads in many cases to the gathering of such food by the mother or nurse. Thus, wasps catch flies; worker ants make raids and carry off weak insects of many kinds; bees gather nectar
flowers
Most Hymenoptera are of moderate or small size, the giants of the ordercertain saw-flies and tropical digging-wasps--never reach the bulk attained by the largest beetles, while the wing-spread is narrow compared n ith that of many dragon-flies and moths. On the other hand, there are thousands of very small species, and the tiny " fairy-flies " (Mymaridae), whose larvae live as parasites in the eggs of various insects, are excessively minute for creatures of such complex organization. Hymenoptera are probably less widely distributed than Aptera, Coleoptera or Diptera
interest
Fossil History.Very little is known of the history of the Hymenoptera previous to the Tertiary epoch, early in which, as we know from the evidence of many Oligocene and Miocene fossils, all the more important families had been differentiated. Fragments of wings from the Lias and Oolitic beds have been referred to ants and bees, but the true nature of these remains is doubtful. Classification.Linnaeus divided the Hymenoptera into two sectionsthe Terebrantia, whose females possess a cutting or piercing ovipositor, and the Aculeata, in which the female organ is modified into a sting. This nomenclature was adopted by P. A. Latreille and has been in general use until the present day. A closely similar division of the order results from T. Hartig's character drawn
Symphyta. This sub-order, characterized by the " sessile," broad-based abdomen, whose fiist segment is imperfectly united with the thorax, and by the usually caterpillar-like larvae with legs, includes the various groups of saw-flies. Three leading families may be mentioned. The Cephidae, or stem saw-flies, have an elongate pronotum, a compressed abdomen, and a single spine on the shin of the fore-leg. The soft, white larvae have the thoracic legs very small and feed in the stems of various plants. Cephus pygmaeus is a well-known enemy of corn crops. The Siricidae (" wood-wasps ") are large elongate insects also with one spine on each fore-shin, but with the pronotum closely joined to the mesothorax. The ovipositor is long and prominent, enabling the female insect to lay her eggs in the wood of trees, where the white larvae, whose legs are excessively short, tunnel and feed. These insects are adorned with bands of black and yellow, or with bright metallic colours, and on account of their large size and formidable ovipositors they often cause needless alarm to persons unfamiliar with their habits. The Tenthredinidae, or true saw-flies, are distinguished by two spines on each fore-shin, while the larvae are usually caterpillars, with three pairs of thoracic legs, and from six to eight pairs of abdominal pro-legs, the latter not possessing the hooks found on the pro-legs of lepidopterous caterpillars. Most saw-fly larvae devour leaves, and the beautifully serrate processes of the ovipositor are well adapted tor egg-laying in plant tissues. Some saw-fly larvae are protected by a slimy secretion (fig. 6, c) and a few live concealed in galls. In the form of the feelers, the wing-neuration and minor structural details there is much diversity among the saw-flies. They have been usually regarded as a single family, but W. II. Ashmead has lately differentiated eleven families of then. A pocrita. This sub-order includes the vast majority of the Hymenoptera, characterized by the narrowly constricted waist in the adult and by the legless condition of the larva. The trochanter is simple in some genera and divided in others. With regard to the minor divisions of this group, great difference of opinion has prevailed among students. In his recent classification Ashmead (11901) recognizes seventy-nine families arranged under eight " super-families." The number of species included in this division is enormous, and the multiplication of families is, to some extent, a natural result .of increasingly close study. But the distinctions between many of these rest on comparatively slight characters, and it is likely that d a_ e. TER2t._. After Marlatt, Ent. Circ. 26, U.S. Dept. Agric. the future discovery of new genera may abolish many among such distinctions as may now be drawn
rsa2 After Howard, Ent Tech. Bull. s U.S. Dept. Agric. d, Its head more highly magni- c, Pupa of male. fled. e, Feeler. and the true wasps, make up the Vespoidea. The Apoidea censists of the bees only. Cynipoidea.In this division the ovipositor sues fawn the ventral surface of the abdomen; the pronotum reaches back to the tegulae; the trochanter has two segments; the fore-wing (fig. 4, 2) has no stigma, but one or two areolets. The feelers with twelve to fifteen segments are thread-like and straight. All the insects included in this group are small and form two familiesthe Cynipidae and the Figitidae. They are the " gall-flies," many of the species laying eggs in various plant-tissues where the presence of the larva causes the format ion of a pathological growth or gall, always of a definite form and characteristic of the species; the " oak-apple " and the bedeguar of the rose are familiar examples. Other flies of this arc toothed. (For the habits of these insects see WasP.) The group have the inquiline habit, laying their eggs in the galls of Chrysididae or ruby wasps are small insects with a very hard cuticle other species, while others again pierce the cuticle of maggots or exhibiting brilliant metallic colours--blue, green and crimson. aphids, in whose bodies their larvae live as parasites. Only three or four abdominal segments are visible, the hinder seg- C'halcidoidea.This division resembles the Cynipoidea in the ments being slender and retracted to form a telescope-like tube in position of the ovipositor, and in the two segmented trochanters. which the ovipositor lies. When the ovipositor is brought into The fore-wing also has no stigma, and the whole wing is almost use this tube is thrust out. The eggs are laid in the nests of various destitute of nervures and areolets, while the pronotum does not bees and wasps, the chrysid larva living as a " cuckoo " parasite. reach back to the tegulae, and the feelers are elbowed (fig. 7). The The Trigonalidae, a small family whose larvae are parasitic in vast majority of this group, including nearly 5000 known species, wasps' nests, also probably belong here. are usually reckoned as a single family, the Chalcididae, comprising The other families of the Vespoidea belong to the series of " Fos-small insects, often of bright metallic colours, whose larvae are sores " or digging-wasps. In two of the families--the Mutillidae parasitic in insects of various orders. The " fig-insects," whose and Thynnidaethe females are wingless and the larvae live as presence in ripening figs is believed essential to the proper develop- parasites in the larvae of other insects; the female Mutilla enters ntent of the fruit, belong to Blastopkaga and other genera of this humble-bees' nests and lays her eggs in the bee-grubs. In the other family. They are remarkable in having wingless males and winged families both sexes are winged, and the instinct and industry of the females. The " polyembryonic " development of an Encyrius, as females are among the most wonderful in the Hymenoptera. They studied by P. Marchal, is highly remarkable. The female lays her make burrows wherein they place insects or spiders which they have egg in the egg of a small ermine moth (Hyponomeuta) and the egg caught and stung, laying their eggs beside the victim so that the gives rise not to a single embryo but to a hundred, which develop young larvae find themselves in presence of an abundant and as the host-caterpillar develops, being found at a later stage within appropriate food-supply. Valuable observations on the habits the latter enveloped in a flexible tube. of these insects are due to J. H. Fabre and G. W. and E. Peckham. The Myntaridae or " fairy-flies " are distinguished from the The prey is sometimes stung in the neighbourhood of the nerve Chalcididae by their narrow fringed wings (figs. 4, 5) and by the ganglia, so that it is paralysed but not killed, the grub of the fossorial situation of the ovipositor just in front of the tip of the abdomen. wasp devouring its victim alive: but this instinct varies in perfection, They are among the most minute of all insects and their larvae are and in many cases the larva flourishes equally whether its prey be probably all parasitic in insects' eggs. killed or not. The females have a wonderful power of finding their Ichnenmonoidea.The ten thousand known species included in burrows on returning from their hunting expeditions. Among the this group agree kith the Cynipoidea and Chalcidoidea in the Vespoid families of fossorial wasps, the Fompilidae are the most position of the ovipositor andyin the jointed trochanters, but are important. They are recognizable by their slender and elongate distinguished by the fore-wing possessing a distinct stigma and hind-legs; many of them provision their burrows with spiders. usually a typical series of nervures and areolets (figs. 4, 8). Many of The Sphegidae are parasitic on bees, while the Scoliidae are large, the species are of fair size. They lay their eggs (fig. 8) in the bodies robust and hairy insects, many of which prey upon the grubs of of insects and their larvae belonging to various orders. A few chafers. small families such as the Evaniidae and the Stephan-tdae are in- Sphecoidea.In this division are included the rest of the " digging-eluded here, but the vast majority of the group fall into two large wasps," distinguished from the Vespoidea by the short pronotum families, the Ichneumoni- not reaching backward to the tegulae. They have usually been dae and the Braconidae, reckoned as forming a single, very large familythe Sphegidaethe former distinguished but ten or twelve subdivisions of the group are regarded as distinct by the presence of two families by Ashmead and others. Great diversity is shown in the median (or discoidal) cells details of structure, habits and nature of the prey. Species of in the fore-wing (figs. 4, 7), Sphex, studied by Fabre, provisioned their brood-chambers with while the latter has only crickets. Pelopoeus hunts spiders, while Ammophila catches cater-one (figs. 4, 6). Not a few pillars for the benefit of her young. Fabre states that the last-of these insects, however, 'lamed insect uses a stone for the temporary closing of her burrow, are entirely wingless. On and the Peckhams have seen a female Ammophila take a stone account of their work in between her mandibles and use it as a hammer
destroying plant-eating the earth over her finished nest. The habits of Bembex are of especial insects, the ichneumon- interest. The female, instead of provisioning her burrow with a flies are of great economic supply of food that will suffice the larva for its whole life, brings importance. fresh flies with which she regularly feeds her young. In this instinct Proctolrypoidea. This we have a correspondence with the habits of social wasps and bees. group may be distin- Yet it may he thought that the usual instinct of the " diggingguished from the pre- wasps " to capture and store up food in an underground burrow for ceding by the position the benefit of offspring which they will never see is even more surof the ovipositor at the extreme apex of the abdomen, and prising. The habit of some genera is to catch the prey before making from the groups that follow (with very few exceptions) by their tunnel, but more frequently the insect digs her nest, and then the jointed trochanters of the legs. The pronotum reaches hunts for prey to put into it. back to the tegulae. The Pelecinidaeincluded here by Ash- Apoidea.The bees which make up this group agree with the meadare large insects with remarkably elongate abdomens Sphecoidea in the short pronotum, but may be distinguished from and undivided trochanters. All the other members of the group all other Hymenoptera by the widened first tarsal segment and the may he regarded as forming a single familythe Proctotrypidae, plumose hairs on head and body. They are usually regarded as including an immense number of small parasitic Hymenoptera, not forming a single familythe Apidaebut there is very great a few of which are wingless. Of special interest are the transforma- diversity in structural details, and Ashmead divides them into tions of Platygaster, belonging to this family, discovered by M. fourteen families. The " tongue," for example, is short and obtuse Ganin, and familiarized to English readers through the writings of or emarginate in Colletes and Prosopis, while in all other bees it is Sir J. Lubbock (Lord Avebury). The first larva is broad in front pointed at the tip. But in Andrena and its allies it is comparatively and tapers behind to a " tail " provided with two divergent pro- short, while in the higher genera, such as Apis and Born/net, it is cesses, so that it resembles a small crustacean. It lives in the grub elongate and flexible, forming a most elaborate and perfect organ for of a gall-midge and it ultimately becomes changed into the usual taking liquid food. Bees feed on honey and pollen. Most of the white and fleshy hymenopterous larva. The four succeeding genera are " solitary " in habit, the female sex being undifferentisections. in which the ovipositor is modified into a sting (always ated; but among the humble-bees and hive-bees we find, as in cxserted from the tip of the abdomen) a.nd the trochanters are with social wasps and ants, the occurrence of workers, and the consequent few exceptions simple, form the Aculeata of Linnaeus. elaboration of a wonderful insect-society. (See BEE.) t'ornticoidea.The ants which form this group are readily dis- BIBLIOGRAPHY.The literature of several special families of the tinguished by the differentiation of the females into winged " queens" Hymenoptera will be found under the articles ANT, BEE, ICHNEUMON-and wingless " workers." The pronotum extends back to the wing- FLY, WASP, &c., referred to above. Among earlier students on bases, and the " waist " is greatly constricted and marked by one or structure may be mentioned P. A. Latreille, Families naturelles du two " nodes." The differentiation of the females leads to a complex regne animal (Paris, 1825), who recognized the nature of the social life, the nesting habits of ants and the various industries that " median segment." C. Gerstaecker (Arch f. 1V'aturg. xx., 1867) thy pursue being of surpassing interest (see ANT), and F. Brauer (Sitzb. K. Aka$. Wiss. Wien. lxxxv., 1883) should Vespoidea.This section includes a number of families char- also be consulted on this subject. Fcr internal anatomy, specially acterized by the backward extension of the prothorax to the tegulae the digestive organs, see L. Dufour, Memr savants strangers, vii. and distinguished from the ants by the absence of " nodes " at the (1841), and Ann. Sci. Nat. Zool. (4), i. 1854. For nervous system Fl. base of the abdomen. The true wasps have the fore-wings folded Viallanes, Ann. Sci. Nat. Zool. (7), ii. iv. 1886-1887, and F. C. lengthwise when at rest and the fore-legs of normal buildnot Kenyon, Journ. Comp. Neurol. vi., 1896. For poison and other specialized for digging. The Vespidae or social wasps have " queens " glands, see I.. Bordas, Ann. Sci. Nat. Zool. (7) xix., 1895. For the and " workers " like the ants, but both these forms of female are sting and ovipositor H. Dewitz, Zeits. wiss. Zoo/. xxv., 1874, winged; the claws on their feet are simple. In the Elimenidar or xxvni., 1877, and F. Lander, ib, 1xvi., 1899. For male genital solitary wasps the female sex is undifferentiated, and the foot claws armature S. A. Peytoureau, Morphologie de l'armure genitale des After Riley and Howard, Insect LiJe,vol. i. F1c. 8.Ichneumon Fly (Rhyssa per- suasoria) ovipositing. insectes (Bordeaux, 1895), and E. Zander, Zeits. wiss. Zool. lxvii., 1900. The systematic student of Hymenoptera is greatly helped by C. G. de Dalla Torre's Catalogus Hymenopterorum (to vols., Leipzig
Bingham
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