As a rule, members of the order Hymenoptera can be regarded as ecological specialists. Most species are rather narrowly adapted to specific habitats and/or specific hosts. Their remarkable success as a taxon probably has more to do with their immense range of behavioral adaptation rather than any physical or biochemical characteristic. The Hymenoptera is the only order besides the Isoptera (termites) to have evolved complex social systems with division of labor. Herbivory is common among the primitive Hymenoptera (suborder Symphyta), in the gall wasps (Cynipidae), and in some of the ants and bees. Most other Hymenoptera are predatory or parasitic. The large hunting wasps are agile predators that catch and paralyze insects (or spiders) as food for their offspring. The greatest diversity, though, is found among the many families of parasitoid wasps whose larvae feed internally on the living tissues of other arthropods (or their eggs). These insects eventually kill their host, but not before completing their own larval development within its body. Despite their small size and characteristically narrow host range, these wasps are highly abundant and exert a tremendous impact on the population dynamics of many other insect species. Most of the Hymenoptera have relatively unspecialized mandibulate mouthparts. An exception is found in the bees (superfamily Apidoidae) where the maxillae and labium are modified into a proboscis that works like a tongue to collect nectar from flowers. In these insects, the mandibles are used to gather or manipulate pollen and wax. Except for worker ants, most adult Hymeoptera have two pairs of wings. Front and hind wings are linked together by hooks (hamuli) along the leading edge of the hind wings that catch in a fold near the back of the front wings. In flight, both wings operate in unison to form a single aerodynamic surface.
Hymenoptera occur in a wide variety of habitats where they are found in the soil and leaf litter or on grasses, shrubs, and trees.