Yet another accidentally introduced Hymenoptera, the European hornet (Vespa crabro) was first found in New York State in 1840 and has since established itself as the only true hornet in North America. Not to be confused with the Vespula we call the white-faced hornet (which is actually an aerial nesting social wasp), V. crabro has some unique characteristics, not the least of which is its size –up to an inch and a half long –and its ability to fly at night. Seeing these large, robust hornets in the beams of flashlights or banging with impressive force against lighted windows can be an unnerving experience, to say the least.
V.crabro is quite colorful, with deep reddish brown markings on the head and thorax and orange or yellow and black stripes on its abdomen. It also has an unusually loud buzz. But for all its size and sound, it is not considered as aggressive as its smaller cousin, the hair-trigger yellow jacket. The old saying, “three stings [from the European hornet] will kill an adult and seven will kill a horse” is not true (unless one is allergic to the venom to begin with).
Still, V. crabro has a formidable stinger and well-endowed poison sac and is near the top of the Schmidt Sting Pain Index (“like a matchhead that flips off and burns on your skin”). And multiple stings by a swarm would be as dangerous and unpleasant as from any of the Vespidae.
European hornets are normally a woodland species with single queens starting new nests each spring, usually inside hollow trees. However, V. crabro will also inhabit abandoned bee hives and enclosed dwelling spaces such as barns, hollow walls and attics; and their enormous foul-smelling nests sometimes completely fill the insides of these structures. Colonies can contain 800 to 1,000 workers attending to several thousand larval cells and two to four combs of specialized queen cells. And unlike other kinds of Vespula colonies, V. crabro nests drip black liquid fecal material. The resulting stench is as much a nuisance as the presence of the hornets themselves.
Oddly enough, there is a type of beetle that lives in peaceful symbiosis with the European hornet. Velleius dilatatus, the hornet rove-beetle, finds crabro nests by its keen sense of smell and moves in, feeding on detritus and attacking brood invaders such as millipedes and centipedes. In return, the beetles are protected by the presence of the hornet colony. Most nests contain an average of seven to ten rove-beetles, each of which gives off its own distinctive sharp, musky odor, thus contributing to the overall perfume.
V.Crabro has the unfortunate habit of girdling twigs and branches of trees and ornamental shrubs, especially lilacs, birch, ash, dogwood, rhododendrons and boxwoods. The hornets chew off the bark to feed on sap that flows into the wound, and to a lesser extent to gather fiber for nest building. All too often, the entire plant dies as a result. The hornets will also spoil ripening tree fruit by puncturing a hole through the skin and hollowing out the insides. On occasion, they will raid honeybee hives.
However, unlike yellow jackets, European hornets are not attracted to human food or garbage. Their main prey is insect pests, and they remove many thousands of flies, grasshoppers, and caterpillars (as well as yellow jackets) from the environment to feed the ever-expanding larval brood.
In this way V. crabro is a beneficial insect, part of the natural ecology. As such, it is protected in Europe, where nest destruction has led to a decline in the species. In Germany, it has been illegal to kill European hornets or destroy any of their nests since 1987, and fines for doing so range up to 50,000 Euros, or about $75,000 American dollars!