Hornets

Hornets 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).

Hornets have stings used to kill prey and defend nests. Hornet stings are more painful to humans than typical wasp stings because hornet venom contains a large amount (5%) of acetylcholine. Individual hornets can sting multiple times; unlike typical bees, hornets and wasps do not die after stinging because their stingers are not barbed and are not pulled out of their bodies.

The toxicity of hornet stings varies according to hornet species; some deliver just a typical insect sting, while others are among the most venomous known insects. Single hornet stings are not in themselves fatal, except sometimes to allergic victims. Multiple stings by non-European hornets may be fatal because of highly toxic species-specific components of their venom. The stings of the Asian giant hornet (Vespa mandarinia japonica) are the most venomous known.

People who are allergic to wasp venom are also allergic to hornet stings. Allergic reactions are commonly treated with epinephrine (adrenaline) injection using a device such as an EpiPen, with prompt followup treatment in a hospital. In severe cases, allergic individuals may go into anaphylactic shock and die unless treated promptly.