Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic.
Females typically have a special ovipositor for inserting eggs into hosts or places that are otherwise inaccessible. This ovipositor is often modified into a stinger. The young develop through holometabolism (complete metamorphosis)—that is, they have a wormlike larval stage and an inactive pupal stage before they mature.
The name Hymenoptera refers to the wings of the insects, but the original derivation is ambiguous. All references agree that the derivation involves the Ancient Greek πτερόν (pteron) for wing. The Ancient Greek ὑμήν (hymen) for membrane provides a plausible etymology for the term because species in this order have membranous wings. However, a key characteristic of this order is that the hindwings are connected to the forewings by a series of hooks. Thus, another plausible etymology involves Hymen, the Ancient Greek god of marriage, as these insects have married wings in flight. Another suggestion for the inclusion of Hymen is the myth of Melissa, a nymph with a prominent role at the wedding of Zeus.
The cladogram of external relationships, based on a 2008 DNA and protein analysis, shows the order as a clade, most closely related to endopterygote orders including the Diptera (true flies) and Lepidoptera (butterflies and moths).
Hymenoptera originated in the Triassic, with the oldest fossils belonging to the family Xyelidae. Social hymenopterans appeared during the Cretaceous. The evolution of this group has been intensively studied by Alex Rasnitsyn, Michael S. Engel, and others.
Phylogenetic relationships within the Hymenoptera, based on both morphology and molecular data, have been intensively studied since 2000. In 2023, a molecular study based on the analysis of ultra-conserved elements confirmed many previous findings and produced a relatively robust phylogeny of the whole Order.