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Hornets are insects, and the largest eusocial wasps. Some species can reach up to 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. ==Life cycle== In ''Vespa crabro'', the nest is founded in spring by a fertilized female known as the ''queen''. She generally selects sheltered places like dark hollow tree trunks. She first builds a series of cells (up to 50) out of chewed tree bark. The cells are arranged in horizontal layers named ''combs'', each cell being vertical and closed at the top. An egg is then laid in each cell. After 5–8 days, the egg hatches, and in the next two weeks, the larva undergoes its five stages. During this time, the queen feeds it a protein-rich diet of insects. Then, the larva spins a silk cap over the cell's opening and, during the next two weeks, transforms into an adult, a process called metamorphosis. The adult then eats its way through the silk cap. This first generation of workers, invariably females, will now gradually undertake all the tasks formerly carried out by the queen (foraging, nest building, taking care of the brood, etc.) with one exception: egg-laying, which remains exclusive to the queen. As the colony size grows, new combs are added, and an envelope is built around the cell layers until the nest is entirely covered with the exception of an entry hole. To be able to build cells in total darkness, it is assumed they use gravity to aid them. They also attach a tiny crystal to the roof of each cell. When the nest substrate is vibrated, the crystals vibrate in a manner depending upon orientation, which allows the wasps to gather information about orientation in the darkness〔(Mystery in a Hornets' Nest )〕 At the peak of its population, the colony can reach a size of 700 workers, which occurs in late summer. At this time, the queen starts producing the first reproductive individuals. Fertilized eggs develop into females (called "gynes" by entomologists), and unfertilized ones develop into males (sometimes called "drones"). Adult males do not participate in nest maintenance, foraging, or caretaking of the larvae. In early to mid autumn, they leave the nest and mate during "nuptial flights". Males die shortly after mating. The workers and queens survive at most until mid to late autumn; only the fertilized queens survive over winter. Other temperate species (e.g. the yellow hornet, ''V. simillima'', or the Oriental hornet, ''V. orientalis'') have similar cycles. In the case of tropical species (e.g., ''V. tropica''), life histories may well differ, and in species with both tropical and temperate distributions (such as the Asian giant hornet, ''Vespa mandarinia''), it is conceivable that the cycle depends on latitude. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hornet」の詳細全文を読む スポンサード リンク
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