Hornets are the largest eusocial wasps, that reach up to 45 millimetres (1.8 inches) 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).

Geographical distribution

The genus Vespa comprises about 20 species, most of which are native to tropical and desert southern Asia, but there is a species found across temperate Eurasia from Britain to Japan, the European hornet (V. crabro), and another, the Oriental hornet (V. orientalis), that extends via southern and central Asia to the Arabian peninsula, up to northern and eastern Africa and the Mediterranean basin (including southern Italy and Sicily). The European hornet V. crabro, was accidentally introduced to North America in 1840 and is now present in many eastern regions; it is the only true hornet in North America. As of 2003, its geographical range extends from the Northeastern United States west to the Dakotas, and south to Louisiana and Florida. Another occurs in temperate eastern Asia, the Yellow hornet (V. simillima), and some tropical species also range as far north as China, Siberia, or Japan. The Asian giant hornet (V. mandarinia) is a native of temperate and tropical Asia.

Life cycle

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. At the peak of its population the colony can reach a size of 700 workers. This occurs in late summer.

At this time the queen starts producing the first reproductive individuals. Fertilized eggs develop into females (called "gynes" by entomologists), unfertilized ones 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.