European Hornets Are A Fall Pest

By Scott Shalaway
IF YOU ARE being menaced by huge night-flying wasps, it’s not your imagination, and you’re not alone.

At few nights ago my wife, called for help. “There’s a huge yellowjacket in the kitchen! Kill it now!” she demanded. At that point, Linda wasn’t really interested in learning about European Hornets, but after the crisis passed, she wanted to know what that beast was.

European Hornets (Vespa crabro) become bothersome in late summer and early fall. They sometimes are attracted to porch lights and fly against windows of brightly illuminated rooms. It can create the illusion that these wasps are trying to attack, but the more likely explanation is that they are hunting other insects attracted to the lights.

Like most one million-plus species of insects that inhabit the planet, European Hornets are usually beneficial. They are predators with a taste for all manner of live insects–crickets, grasshoppers, flies, caterpillars and even other species of wasps. But in the fall, their biology sometimes puts them at odds with homeowners. I first encountered European Hornets two years ago when they spent several weeks attracted to the light outside my office door.

At a glance, European Hornets resemble giant yellowjackets. They measure about 1-1/4 inches long and have a reddish brown head. The abdomen is black with conspicuous yellow markings. They were introduced to the United States sometime in the mid 1800s and now occupy the entire eastern half of the country.

It is the food habits of European Hornets as much as their size that distinguishes them from yellowjackets. Yellowjackets’ taste for people food makes them pests at picnics, fall festivals and tailgate parties. If we’re lucky enough to avoid being stung, they’re eating our burgers or drinking our beer. Hornets prefer live food, though they sometimes eat ripe apples and leave only the skin behind.

In the spring, fertilized female hornets emerge from the winter den, which might be a tree cavity, the space behind a loose slab of tree bark, a rodent burrow, or a hollow wall. Queens then establish new colonies by laying eggs in paper nests they build inside of hollow trees. (The more familiar Bald-faced Hornet, which is actually a type of yellowjacket, builds the paper, basketball-sized nests often seen high in trees.)

When European Hornets stick to wooded areas, they live their lives unnoticed by people; but when they build nests inside hollow walls of homes and other buildings, conflict with humans is likely.

The queen’s first brood emerges as sterile female workers. They take over the responsibility of feeding subsequent broods and enlarging the paper nest. They also defend the nest from intruders.

In mid-summer, fertile males and females are produced. These individuals mate and the impregnated females become the next year’s queens. By late September, a typical European Hornet colony contains 300 to 400 workers, but in large colonies the population can exceed 800.

Unlike other wasps, hornets forage at night. That’s why we see them at porch lights or striking window panes. So, if you’re seeing huge wasps around the house, you may have a hornet nest in an exterior wall. Hornets can sting repeatedly and they actively guard the nest entrance. Fortunately they are not as aggressive as yellowjackets, so if you don’t disturb them, coexistence is possible.

One word of warning: Do not plug the entrance to the nest in hopes of confining the hornets to the hollow wall. Trapped hornets may chew out another exit into the inside of the house. The last thing you want is 400 hornets in the living room.

If living with hornets is more than you can bear, call an exterminator and let a professional solve the problem. It will be money well spent.

Fortunately, the hornet colony will die off naturally in the next eight weeks. By late November, hard frosts kill all the workers. Only pregnant females–the future queens–survive the winter and old nests are not reused.

Understanding the lives of annoying creatures may not eliminate the threats they pose, but it’s usually reassuring to learn the problem is temporary. –Pittsburgh Post Gazette