"Murder" Hornets

One August evening, as I reached for the doorknob, an enormous yellowjacket landed on the screen door at my eye level. It takes a lot for an insect to startle me, and this creature certainly did! Looking out of the door, I observed six giant insects swarming the porch light. I took a deep breath and introduced myself to a European hornet.

I met those European hornets fifteen years ago when the family's schedule kept the porch light on continuously. Since then, I've seen a few of these impressive insects annually. I had received only one inquiry for European hornet identification in ten years. Suddenly, the calls, texts, and emails poured in about two years ago. What changed? Were these large and scary insects becoming more common? No! Giant hornets (Vespa mandarinia) had been discovered near the Canadian border in a small area of Whatcom County, Washington, and Fraser Valley, British Columbia. The media dubbed these Asian insects "murder hornets." Probably due to media hype, Pennsylvanians two thousand miles away were concerned about them!

Michael J. Skvarla, entomologist at Penn State University, and colleagues from Wisconsin and North Carolina have documented the significant increase in requests for large wasp, yellow jacket, and hornet identification since May 2020. The summer 2022 edition of American Entomologist published their report. They believe that the influence of COVID-19 compounded the publicity given to the giant hornets. Many persons avoided public spaces and stayed home. This led to people being more aware of the insects around their homes. Many turned to outdoor hobbies such as gardening, which exposed them to unfamiliar insects. The population of large hornets, mainly European hornets, did not increase, just the awareness, curiosity, and concern about them.

European hornets (Vespa crabro) were discovered in New York in 1840 and have spread throughout all the eastern states. European hornets are the only true hornet found in eastern North America. What we commonly call bald-faced hornets (Dolichovespula maculata) are considered black and white yellowjackets. Common names are often misleading. The European hornets make tan-colored paper nests inside hollow trees, between walls, or in attics. The colony does not survive the winter but fertilized queens overwinter individually as foundresses. One foundress forms a colony of 200 to 400 workers by the end of the season.

European hornet (Vespa crabro) Photo (left): Steve Jacobs, Penn State. Photo (right): David Stephens, Bugwood.org.

Adult female European hornets are about 1.25 inches long. These exotic hornets have broad yellow bands on dark brown abdomens with russet hairs on the thorax. By comparison, native bald-faced hornets are only 0.5 to 0.75 inches long. Unlike other wasps, European hornets forage by day and also at night. They are attracted to incandescent lights and may feed on other insects flying around those lights. By day, they feed on large insects like grasshoppers and bees. They also feed on fruit, tree sap, and honeydew from aphids and spotted lanternflies. Unlike other species of wasps, the European hornet will hunt in groups. Like other wasps, yellow jackets, and hornets, they feed prey insects to their larvae.

European hornets strip off the bark from trees and shrubs to construct their paper nests. They favor lilac, birch, willow, boxwood, mountain ash, poplar, and occasionally rhododendron. They also feed on the sap that oozes from the damaged stem.

What should you do if European hornets feed on your shrubs, especially lilacs? In reality, they rarely cause permanent damage to the plants. Wait until late autumn to see if the branches require pruning. Currently available insecticides have little residual activity, so applying products to the limbs has limited effect. Some aerosol sprays have a fast knockdown, but these huge hornets may survive.

How can you prevent European hornets from gathering on your porch at night? Don't leave the porch light on, switch to yellow light bulbs, or install a motion-activated lamp. Currently, there is no conclusive research on repellents for European hornets.

Treating European hornet colonies is dangerous as they defend their nests aggressively. If a nest does not threaten people, it should be left alone, as it will die naturally during the winter. Homeowners should hire a pest control professional if a nest is in or near a house. European hornets have smooth stingers, so each can sting repeatedly. Their stings also carry venom, making them hurt, itch, or swell for about 24 hours. A European hornet sting has the same risk of allergic reactions as other wasp stings, not more.

The eastern cicada killer wasp (Specius speciosus), 1 to 2 inches long, is also found in our area. This native wasp is black with a few light-yellow markings and a narrow, pointed abdomen. It is a solitary wasp, not colonial. Although each cicada killer nests individually in sandy soil, it may have several close neighbors. The patrolling males put on a good show but cannot sting. The females paralyze large prey, like annual cicadas, and carry them back to their burrows to nourish the young. These are frightening but generally harmless creatures.

Eastern cicada killer wasp. Photo: USDA Forest Service - Coeur d’Alene Field Office , Bugwood.org

Asian giant hornet. Photo: Washington State Department of Agriculture, Washington State Department of Agriculture, Bugwood.org

The United States Department of Agriculture offers photos that compare the Asian giant hornet with other large wasps. This giant hornet has been closely monitored, trapped, and exterminated in a small area of northwestern Washington state since 2020. "Murder hornets" voraciously feed on insects, especially colonies of bees and other wasps. As of June 2022, researchers had no positive sightings of giant hornets in Washington or British Columbia. The giant hornet is not in Pennsylvania. If you have questions or concerns about huge wasps, yellow jackets, or hornets, please reach out to the Penn State Extension office in your county. Master Gardener volunteers staffing the Garden Hotline will assist you.