They are dark brown with yellow or yellow-orange striping. They are not fuzzy like bees, but have the solid body shape similar to bees and yellow jackets. What makes European hornets most recognizable is their size. At 1-1.5 inches (26-38mm) they are twice the size of most wasps, and are the only true hornet found in the United States. European hornets build large aerial nests in out-of-the-way places such as hollow trees, high up in old barns, or on the sides of buildings that see very little human activity. Colony size is 300-500 wasps, sometimes more. European hornets forage for insect prey, fruit and plant sap, and are attracted to lights while foraging at night. Their foraging for wood fiber and sap often leaves damage on soft or young tree bark.
Like other wasps, European hornets build large, round, papery nests created from chewing the fiber (cellulose) of wood, and create cells inside for raising the brood. There are several horizontal layers (called combs) of cells. Those cells are protected by on outer covering, sometimes called an envelope. Nests resemble the large gray oval structures of bald-faced hornets but are tan and have a ragged shape, and uneven edges and openings.
Nests are started by overwintering mated queens in early spring, and once she’s raised a few workers, they take on the task of building and feeding while the queen focuses on egg-laying. Only females have stingers because a stinger is a modified ovipositor (egg-layer). Male hornets are among the last raised in a nest, and only function to mate with the new queens. European hornets are calm when foraging but can be aggressive when protecting the nest.
The occasional sighting is not a concern, and foraging hornets are rarely a danger unless provoked by a perceived threat. Your best bet is to scout for places where a nest could be hidden and therefore cause problems if humans or pets startle its occupants—this is true of all wasps, bees and hornets. Here are tactics to reduce wasp problems, and they apply to European hornets too:
- Avoid wearing perfumes, fragrant or flowery lotions, shampoos, conditioners and soaps.
- Avoid swatting at wasps and hornets, or squashing them; crushed hornets emit a scent that may attract nest-mates. Gently blow off, or brush off a wasp that has settled on you.
- Avoid walking barefoot in lawns with clover or other flowering weeds.
- Scoop live wasps out of swimming pools and place them away from busy areas.
- Watch for signs of nests by hornet activity, and remember to look up. Doing this, a tactic called scouting, in the spring helps you find nests while their population is small. In spring and summer, look in areas on your property that have been dormant. This is especially true while using equipment like tractors or boats that sat idle through the spring.
Never rely on insect ‘fogger’ products to control wasps and hornets in an open space. If there is any concern about a stinging insect nest, consult a professional pest management company or beekeeper.
You may see them foraging for insects in your yard or resting in the sun. Unless a nest is nearby, you will likely not see more than one or two each season because they tend to avoid busy areas. If you have old hollow trees or decaying structures on your property, there could be a colony of European hornets inside. If left alone, they will not bother you.
The best way to reduce problems is to prevent them. Learn to scout for signs of wasp and hornet activity in spring and early summer. In most cases, hornet nests are up inside hollow trees, old barns or protected sides of buildings, and away from human and pet interaction. Therefore, despite European hornets’ size, they are unlikely to be a problem. If you find a large nest which can’t be ignored, call your local cooperative extension for recommendations of an experienced pest control expert.
Here’s a timeline for best management against wasp and hornet problems:
Early spring through summer: Monitor buildings and grounds for stinging insect activity on warm sunny days; try to do this every other week. Watch up high for foraging European hornet workers and where they travel to and from. They will never be in a ground nest.
Late summer through fall: Continue to monitor buildings and grounds. If you find a nest that you can keep isolated from people and pets, leave it be. Remember that once the brood is raised, adults will leave the nest. Minimize food and food trash when possible in outdoor seating areas, although European hornets are not scavengers. Consult an expert if you find an active colony that poses a stinging risk to people and pets.
Winter: Plan a prevention strategy for the following season. Raise awareness among your family and neighbors or building staff about how using IPM can reduce stinging insect risks for the following season. For all other wasps and hornets—seal holes in wall voids and roof eaves in the cold weather season. After grasses have died down, it’s a good time to look for areas in soft soil where rotted wood or old animal burrows accommodate ground nests. Fill in holes and compress the soil. Fall or early spring is also a good time to check and fix flashing in eaves where wasps (and insects) can enter buildings.
Always have an action plan in place to care for people and animals who have been stung.