Hornets are insects that are the largest eusocial wasps. Some species can reach up to 5.5 cm (2.2 in) in length. The true hornets make up the genus Vespa and are distinguished from other vespines by the width of the vertex (part of the head behind the eyes), which is proportionally larger in Vespa and by the anteriorly rounded gasters (the section of the abdomen behind the wasp waist). The best known species is the European hornet (Vespa crabro), about 2–3.5 cm in length, widely distributed throughout Europe, Russia, North America and Northeast Asia. Most species make exposed nests in trees and shrubs, but some (like Vespa orientalis) build their nests underground or in other cavities.
Hornets are found mainly in the Northern Hemisphere. The common European hornet (Vespa crabro) is the best-known species, widely distributed in Europe (but is never found north of the 63rd parallel), in North China and also the only species introduced to North America, Ukraine and European Russia (except in extreme northern areas). In the east, the species’ distribution area stretches over the Ural Mountains to Western Siberia (found in the vicinity of Khanty-Mansiysk). The common European hornet was accidentally introduced to North America about the middle of the 19th century, and has lived there since at about the same latitudes as in Europe. However, it has never been found in western North America. In Asia, the common European hornet is found in southern Siberia, as well as in eastern China.
The Asian giant hornet (Vespa mandarinia) lives in the Primorsky Krai region of Russia, China, Korea, Taiwan, Cambodia, Laos, Vietnam, Indochina, India, Nepal, Sri Lanka, Thailand, but is most commonly found in the mountains of Japan, where they are commonly known as the Giant Sparrow Bee.
The Oriental hornet occurs in semi-dry sub-tropical areas of Central Asia (Iran, Afghanistan, Oman, Pakistan, Turkmenistan, Uzbekistan, Tajikistan), southern Europe (Italy, Malta, Albania, Romania, Turkey, Greece, Bulgaria, Cyprus), North Africa (Algeria, Libya, Egypt, Sudan, Eritrea, Somalia), and along the shores of the Gulf of Aden and in the Middle East. It has been introduced to Madagascar.
The Asian predatory wasp, Vespa velutina has been introduced to France and Spain.