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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Winter survival, Part 1: European hornet, Vespa crabro

 

Fallen pears are a good source of carbohydrates for these giants.

 

Insects use many strategies to survive winter’s cold in chilly regions of the country, including Maryland. Last week while searching through my woodpile, I discovered a very chilly European hornet that had snuggled into my firewood in advance of Old Man Winter. The torpid creature was too drowsy to muster much of a greeting as I picked it up for a look.

By early November, European hornet queens have entered a quiescent state to sustain them through the long winter. 

This encounter was quite different from another meeting with these titans of the hornet world that I had a few years back. One afternoon, I received a phone call from an animated homeowner who had discovered exceedingly large wasps inhabiting an ancient tree in her backyard. After a brief discussion of their nocturnal antics, ferocious appearance, but otherwise gentle demeanor, I informed her that her visitors were likely continental in origin, that is to say European, and perhaps this explained a kind of six-legged civility not normally seen in large stinging insects. A visit to the property revealed a magnificent colony of European hornets living in the trunk of an old silver maple. European hornets were introduced into New York from Europe sometime between 1840 and 1860. They took to the New World, spread steadily, and now occupy territory from the east coast to the Mississippi.

The story of the hornet colony is fascinating. Way back in spring, the colony was founded by a single queen that had survived the winter in a protected spot beneath the bark of a fallen tree or in a woodpile like mine. Upon emerging in spring, the queen discovered the cavity in the maple tree and founded a colony. After the queen successfully raised her first batch of sterile female workers, she remained in the nest producing more offspring while her daughters took up the tasks of enlarging the nest, protecting it, and gathering food to feed the young. On the menu were delectable protein treats, caterpillars, flies, grasshoppers and other stinging insects like yellow jackets.

A hollow tree is a typical nesting site for European hornets.

During late August and early September, the colony operated at a fevered pace. Inside the colony, the queen no longer spawned sterile daughters. She shifted production from workers to female and male wasps capable of reproducing. The females were destined to become the queens of future generations of hornets. The males had just one purpose, namely, to mate with the new queens. After fulfilling this biological imperative, the males died. As autumn wound down, the nest was abandoned and queens searched for protected places to spend the chilly months of late autumn and winter. Abandoned nests are not used in subsequent years.

European hornets are somewhat unique in their foraging behaviors in that they hunt at night. They are also attracted to light and can often be found buzzing around porch lights or heard crashing into windowpanes after dark. European hornets also have a curious behavior of stripping the bark from several types of trees and shrubs including lilac, birch, and rhododendron. Apparently, this annoying behavior allows them to feed on the nutritious sap and plant tissues beneath the bark. Unfortunately, small plants may be severely damaged by this bark stripping.

Trees with thin bark are often ravaged by bark-stripping European hornets in late summer and autumn.

Although these hornets are large and scary looking, humans are unlikely to be stung. I photographed hornets at a very close range and other than receiving an inquisitive stare, I was unmolested. To avoid being stung by these giants, simply avoid disturbing the nest site. Remember, in autumn many stinging insects feast on fallen fruit. To reduce chances of a sting by a European hornet, yellow jacket, or wasp, carefully pick up fallen fruit and compost it. Wear shoes rather than going bare footed when you walk near fruit trees.

This large nest came from a wall void in my neighbor’s home.

If European hornets have nested in a home or another location that poses a threat to human health or safety, they may be exterminated, and assistance from a professional may not be a bad idea. However, if the nest is out of harm’s way, I favor the approach of my neighbors who had a “live and let live arrangement” with a nest of European hornets that had taken up residence in a wall void of their home. They decided to give the nest a respectable berth and simply enjoy the comings and goings of these spectacular insects.

References

Special thanks to Harry for alerting me to the hornets in his lilacs, to Brooke and Ruth Ann for sharing their ginormous hornet's nest, and to the wonderful family with hornets in their maple tree.