Hymenoptera (Greek hymen, "membrane;" pteron, "wing"), order of insects containing more than 100,000 species, including ants, bees, wasps, sawflies, chalcids, and ichneumons. Some species of this order have highly complex social structures, although most are solitary, parasitic, or parasitoid (slowly killing the host near the end of the parasite's larval development).
Hymenopterans have mouthparts adapted for chewing or biting. In some higher hymenopterans, such as bees, the mouthparts are further modified in a way that enables the insects to draw nectar from flowers. Hymenopterans typically have two pairs of membranous wings, the forewings being larger than the hind wings. Some species, however, are wingless. The ovipositor (egg-laying organ of the female) is usually well developed and used in various ways for depositing eggs. In the higher hymenopterans it is modified into a stinger used by females only, for defense or offense. The stinger is reduced or lost in some species or groups of species. Young hymenopterans metamorphose completely from eggs, to larvae, to pupae, to adults. The more primitive hymenopterans, such as horntails and sawflies, lack the distinct constriction or wasplike "waist" between the thorax and abdomen found in the higher hymenopterans (ants, wasps, and bees). Primitive hymenopterans have larvae that bear thoracic legs, but the larvae of higher hymenopterans are legless. Ants and some wasps and bees are social, living in well-integrated colonies, individual members of which are morphologically specialized for performing distinct functions. The social structure of some hymenopterans is more complex than that of any other invertebrates except termites.
Hymenopterans are very diverse in morphology and biology. They are one of the most beneficial groups of insects from the point of view of humans, although some members are highly destructive. Among the latter are some sawflies, the larvae of which feed on plants. On the other hand, the ichneumons and chalcids are parasites that destroy harmful insects. Still other hymenopterans, including bees and various kinds of wasps, are of great importance to humans because of their role as pollinators of food and forage crops.
Scientific classification: The order Hymenoptera belongs to the class Hexapoda.