Large, scary hornets stripping bark from trees, eating fruit, and going “bump in the night”: European hornet, Vespa crabro

During the waning weeks of summer, messages pour in about large hornets bumping into windows at night, stripping bark from trees and shrubs, or simply frightening folks with their presence. Throughout the last two years, these giants of the wasp world were often mistaken for dreaded “murder hornets”, an invasive scourge of honeybees and beekeepers in the Pacific Northwest. Ergo, now is a good time to visit another foreigner, the European hornet, that calls the United States home. European hornets first appeared in the US in New York sometime between 1840 and 1860.These predators spread and now occupy territory from the east coast to the boarders of the Dakotas. In nature, European hornets use a tree cavity as the location for a nest, but occasionally, as was the case with my neighbor across the street, hornets will nest in a wall void.

The colony is founded by a single queen that survives the harsh winter beneath the bark of a fallen log or in a similar protected location. In spring when warmer temperatures return she becomes active, gathering bark from trees, constructing a small paper nest, and laying eggs destined to become workers. After the queen successfully raises her first batch of sterile female workers, she remains in the nest producing brood while her daughters take up the tasks of enlarging the nest, protecting it, and gathering food for the young. Caterpillars, flies, cicadas, grasshoppers and other stinging insects like yellowjackets are all on the menu. European hornets are somewhat unique from other clan members such as yellowjackets and baldfaced hornets in their foraging behaviors. European hornets hunt at night. They are also attracted to light and can be found buzzing around porch lights or heard crashing into windowpanes after dark. Several times this past month while reading in bed, European hornets were the “things that go bump in the night” at my bedroom windows.

In addition to eating other insects, in late summer and early autumn European hornets readily dine on fallen fruit and sap fluxes on tree bark. They engage in a somewhat unusual behavior of feeding on plant tissues beneath the bark of trees and shrubs. A visit to one of my neighbor’s lilacs revealed mischievous European hornets stripping bark and greedily lapping exudates leaking from the wound. This annoying behavior has been observed on many types of trees and shrubs including lilac, rhododendron, ash, and birch. Unfortunately, small trees and shrubs can be severely damaged by this behavior. Many stinging insects feast on the sweet bounty of fallen fruit beneath trees. To reduce chances of a sting by a European hornet, yellowjacket, or wasp, don protective gloves and carefully pick up fallen fruit and compost it if it poses a risk. Wear shoes rather than going barefoot when you walk near fruit trees.

Tree hollows are typical nesting sites for European hornets in the wild. Cicadas and other insects serve as protein sources for developing larvae back at the nest. Hornets often imbibe liquid nutrients from sap fluxes on tree trunks. Powerful jaws strip bark from trees to be used in nest construction and also to expose nutritious tissues just beneath the bark. Bark feeding is common on many trees and shrubs in late summer and early autumn. To get up close and personal with these hornets, wait until late autumn when stingless drones can be found.

During autumn, the hornet colony operates at a fevered pace. Inside the colony, the queen no longer produces sterile daughters. She has shifted production from workers to female and male hornets. Females are destined to become queens of future generations. Males have just one purpose and that is to mate with the new queens. After fulfilling this biological imperative, males die. As autumn wanes, the colony is abandoned and queens find protected places to spend the chilly months of late autumn and winter. The nest will not be reused in subsequent years.

Although these hornets are large and scary looking, humans are unlikely to be stung by European hornets. I have photographed and video-recorded these gentle giants at a very close range and other than receiving an inquisitive stare, I was unmolested. To avoid being stung, simply avoid disturbing the nest site or the hornets. If European hornets have nested in a home or another location that poses a threat to human safety, they may be exterminated. 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 these giants 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.

Acknowledgements

Special thanks to many Master Naturalists and homeowners for sending images of European hornets, which served as the inspiration for this episode. Thanks to Dr. Shrewsbury for sharing videos of European hornets, Harry for directing me to his pillaged lilacs, and to Brooke and Ruth Ann for sharing a ginormous hornet’s nest that once resided inside their wall.

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