People are alarmed by them, which is not surprising when what looks like a giant wasp is buzzing around trying to escape through the window, but our native hornets would rather get away from humans and are valuable part of our biodiversity.
The largest of our social wasps, the European Hornet can be seen from May to November, most often in woodland glades where they build nests in hollow trees. New queens emerge and mate in late autumn and then hibernate. All the other hornets including the old queen die off before the onset of winter.
The new queen will do not return to the existing nest but start building a new one when she emerges in spring. The nest is made of plants chewed to make a papery material. Once workers are born they take over to support the queen and brood while the queen gets on laying eggs. The nest can be the size of a football and be home to about 400 hornets, compared with the 3-6,000 in a wasp nest.
Worker hornets are all female but usually have a sting instead of ovaries and no egg laying device called an ovipositor and they do not lay eggs. Occasionally egg laying workers are born but their eggs and grubs have a different chemical signal and the other workers will not feed them so they die.
The workers feed on nectar and so are active pollinators, but they hunt many species of insects to feed the young larvae. The insects are chewed up by the workers before being fed to the larvae. Prey include pest species such as the wax moth, a parasite of honey bee hives. In some parts of Europe bee keepers actually encourage hornets to nest near their hives. The hornets will catch a few bees, but they reduce the chance of a serious infestation of the wax moth caterpillars which feed on the bee grubs and cocoons.
Hornets really would prefer to stay away from humans and they are less aggressive than common wasps but, if you threaten their nest they will attack and sting. They also scavenge on human food waste in the autumn and will defend a food source. They are larger than wasps and so the sting is more painful.
The Asian yellow-legged hornet is an invasive pest that has spread across Europe and first arrived in the UK in 2016 in Gloucestershire. Unlike the European hornet which are beneficial insects even for honey bee hives, the Asian cousin is a voracious predator and can devastate hives.
Each summer there is a wave of press and social media hysteria about them, but they are still very rare with only two confirmed cases in Devon. If you see an Asian hornet then you should report it. As the name suggests, the invasive species has yellow legs while the native species has dark lower sections of the legs. More easy to see, the native hornets are a reddish orange while the Asian hornets are almost black.
Ed Dolphin
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