HYMENOPTERA, hi-men-6p'te-ra, an order of Hexapoda or insects, considered by many entomologists to be the highest and most perfect expression of the insect type. The meta morphosis is complete and extensive. The larvae are short, thicic grubs, footless except in the saw-flies (Tenthredinic(e) and in most cases are carefully nurtured and fed in nests. The pupae have nearly the form of the perfect in sects. The imagos are of compact, highly com plex construction, with the three regions well marked, except that the first segment of the abdomen is united with the thorax. A consid erable part of the large head is occupied by the conspicuous compound eyes, besides which there are three ocelli. The jaws or are conspicuous biting organs, and the remaining mouth-parts usually form more or less of a proboscis with a large ligula or tongue. Al though the wings are small, they move with great rapidity and sustain the body in rapid and extended flight; there are two pairs (usually), membranous, veined and transparent. The hymenoptera are divided by Linnaeus into two sections, the Terebrantia, which have an ovipositor instead of a sting in the female, and the Aculeata whose females have a sting. more generally accepted division regards the saw-flies as a jrimitive sub-order, having no waist or constncted region at the middle, and an incomplete union of the first abdominal seg ment with the thorax, and also having thoracic and often abdominal legs in the larval stage.
Marked sexual dimorphism is very frequent especially among the social forms, in which a third class of individual, the worker or neuter, in reality imperfect females, also occurs. Many
of the ant communities are still farther poly morphic. The order is one of great extent and exceptional interest, as it includes the ants, bees and wasps, the ichneumon-flies, gall-flies and saw-flies, divided into numerous families. Among the ants and bees are exhibited most re markable and complex social states, which are described in the articles on these groups. The habits of the numerous species of wasps, and especially the varied architecture of their nests, of nearly equal interest. A remarkable series of adaptations to special conditions are presented by the parasitic ichneumon flies and their allies, which lay their eggs within the bod ies of the larvae or even in the eggs of other Insects, on the substance of which their own larva feed. Confining their parasitism to plants, the gall-flies produce by the irritation caused by their eggs or secretions deposited with them in the tissues of leaves, twigs or fruits, the famil iar excrescences whose shapes are almost as numerous as the species which produce them. (See GALLS). Finally, the saw-flies are least typical of the order but stand nearest to the main hexapod stem. Their larvae have both thoracic and abdominal legs and closely re semble caterpillars; they are vegetarians and many of them are very destructive to plants. Consult standard works of Entomology (see INSECTS), and the bibliographical list given by L. O. Howard in the appendix to his Book' (New York 1902).