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Gardening Lessons on the EUROPEAN HORNET
Posted on Tuesday 7/13
Origins of the European Hornet - a Menace to our Natural Landscapes
The European hornet is a nonnative U.S. pest that has a home range extending throughout Europe. This wasp species was first discovered in the northeastern U.S. around 1854. The European hornet can now be found ranging throughout the eastern U.S. and west into Louisiana and the Dakotas.
European hornets are easy to recognize. The adult females often exceed 25-mm (I-inch) in length. Like many wasps, European hornets have broad yellow bands on the abdomen, but can be distinguished by reddish-brown markings on the prothorax ("neck") and head and wings that are brownish in color.
Unlike other wasps, European hornets are also active at night. They are attracted to incandescent lights during summer and fall evenings. Yellow-colored or sodium vapor light bulbs are less attractive to the European hornet, and can be used if hornets are a problem. European hornets are the only "true" hornets in North America. Because the term hornet refers only to wasps in the genus Vespa, scientifically, the bald-faced "hornets" (Dolichovespula sp.) are more closely allied to yellow jacket wasps.
Pest Problems Associated with the European Hornet
Hornets feeding on pest insects in agricultural crops can be beneficial. However, European hornets can cause injury or loss to fruit crops, as well as damage to trunks and stems of ornamental plants in the nursery and landscape.
European hornet injury is most common on lilac, birch, willow, boxwood, mountain ash, white and green ash, poplar, and occasionally Rhododendron. Damage occurs when worker wasps chew on the bark of tree and shrub limbs. The hornets use the chewed pulp to build their paper nest.
European hornet colonies are seldom established underground and rarely, if ever, occur in evergreen tree cavities. In April, young queens lay up to two dozen eggs in a linear, paper-cell comb suspended on a stalk made from chewed plant fibers. Until her young mature, European hornet queens must forage to provide food and shelter to their developing brood.
A European hornet nest may consist of 200 to 400 individuals (with larger colonies numbering more than 1,000 hornets). The majority of colony inhabitants are sterile female workers. The worker caste is responsible for foraging, colony defense, and maintenance of the nest, which may consist of six to nine tiers of paper combs and over 3,000 individual brood cells.
Within combs, individual cells must be large enough to accommodate developing larvae and pupae. For this reason, European hornet nests can be as large as many yellow jacket wasp nests, which can support populations sometimes exceeding 4,000 individuals European hornets rarely forage around picnic areas or garbage like yellow jackets, so they generally cannot be baited for purposes of colony location.
The stem- or trunk-girdling nature of hornet injury can kill individual branches or the canopy of young trees. Injury is often misdiagnosed as feeding damage from squirrels or rodents, which will result in unsuccessful management decisions.
Both European hornets and yellow jacket wasps are extremely aggressive when their colonies are disturbed. Multiple stings are possible, but reactions are generally limited to localized pain that dissipates with time. However, the human health risk from anaphylactic shock and allergic responses to hornet, wasp, and bee venom is a very real concern