Although adult worker European hornets have a striking resemblance to yellow jackets -- a native wasp of the United States -- they are much larger. As adults, these hornets grow up to 1 1/2 inches long. On their heads and thoraxes, European hornets are dull yellow or light brown. The abdomens of these insects are black with yellow markings. European hornets are also confused with bald-faced hornets, a wasp native to the United States. Bald-faced hornets are not true hornets. Queen European hornets are larger than the workers and feature reddish and black patterns.
European hornets generally construct their nests and colonies in forests in the spring and summer, using tree cavities to provide their nests with shelter. In urban or agricultural areas, European hornets build nests in the holes and crevices of man-made structures such as barns and houses. In contrast to American wasps, European hornets do not build nests in exposed areas or underground burrows. During the winter, queen European hornets leave their nests and repeat the process of finding nesting sites to start colonies.
In the summer months, European hornets are primarily nocturnal creatures. They are drawn to lights such as porch lights, streetlights and camp fires. Sometimes European hornets bump into glass doors and windows in an attempt to reach the light inside a house. Under normal circumstances, European hornets are not as aggressive toward humans as other hornet species. However, they will attack people who accidentally stray too close to their nest.
Because they are only native to Europe, European hornets do not have any natural predators in the U.S., so their populations are only maintained by pest control companies. European hornets can cause great damage to trees by stripping the bark for sap. They also pose a problem for man-made buildings with wooden infrastructures. However, European hornets are also beneficial for gardening and agriculture because they prey on insect pests. Entomologists caution that homeowners should not try to eradicate European hornets that are nesting inside buildings and should instead consult a professional pest control service.