Hornets are wasps of the genus Vespa in the subfamily Vespinae (the vespine wasps). They are the largest of the eusocial wasps, with some species reaching 5.5 cm (2.2 in) in length. They are similar in appearance to their close relatives the yellowjackets, but are distinguished from other vespine wasps by the relatively large top margin of the head. Worldwide, 22 species of Vespa are recognized. Most species only occur in the tropics of Asia, though the European hornet (V. crabro) is widely distributed throughout Europe, Russia, North America, and north-eastern Asia. Wasps of the genus Dolichovespula native to North America are commonly called hornets (e.g., bald-faced hornet), but are actually yellowjackets.
Like other social wasps, hornets build communal nests by chewing wood to make a papery pulp. Each nest has one queen, which lays eggs and is attended by workers that, while genetically female, cannot lay fertile eggs. Most species make exposed nests in trees and shrubs, but some (such as Vespa orientalis) build their nests underground or in other cavities. In the tropics, these nests may last year-round, but in temperate areas, the nest dies over the winter, with lone queens hibernating in leaf litter or other insulative material until the spring. Male hornets are docile and do not have stingers.
