The genus Vespa, commonly known as the hornets, comprises of mostly medium to large wasps; some of the largest social wasps belong to this group. They are distributed mainly across tropical Asia, with some species ranging as far north as temperate Japan and Russia; one species, the European hornet (Vespa crabro) is widely distributed in European regions and introduced to North America, and another, the oriental hornet (Vespa orientalis), is found in the Middle East and the Mediterranean region.
Hornets are close relatives of the yellowjackets. They are similar in shape but generally much larger, with a far wider and stronger head profile.
Hornets make nests with multiple combs and an outer envelope. The nest is usually round or oval in shape, and the structure can vary. Due to their large size, hornet nests are often large, although the colony size can vary. Some species nest high in trees, while others use hollow crevices such as tree hollows or sometimes, cavities inside hollow walls. Yet others nest underground, enlarging the burrow every now and then to allow the nest to grow.
Hornets are greatly feared due to their considerable size and very painful stings, as well as a reputation for being extremely aggressive. This is in fact only partially true. Indeed, hornets and all other social wasps will defend their nests vigorously at any disturbance. However, hornets (and all other wasps) are never out to attack. With care, it is possible to approach the nests of even the more defensive species! It is only when we unknowingly invade their living space that they respond to what they see as a threat. Also, many times, people invariably swat or leap up in natural response to the sudden attack, and this only incites them to further attack. Many species of hornets are quite defensive, but some are very tolerant and easy to approach. In fact, the pest species of yellowjackets may have far more destructive potential.
Most hornets are generalist predators, killing any insect they can overpower. Being large, powerful wasps, they can subdue many different insects, including other smaller wasps and bees, flies, caterpillars, grasshoppers, butterflies and even dragonflies. Some hornets are more specialized in that they frequently attack the nest of paper wasps (Polistes, Parapolybia etc.) and capture the larvae to feed their own larvae. However, even these species will often attack other insects they happen to encounter. They sometimes catch beneficial insects such as certain butterflies and dragonflies; some hornets can also be pests at bee farms, preying on honeybees and disrupting activity. However, hornets are beneficial on the whole, as they actually kill great numbers of pest species. A small number of species (including Vespa bicolor, Vespa affinis, Vespa orientalis, Vespa simillima, Vespa velutina) frequently collect meat from freshly dead animals, rotting carrion or even cooked meat meant for our consumption, but the majority of species prefer to hunt live insects.
There are probably twenty-odd known species of hornets.