Over the past three to four years, a new insect, the European paper wasp, has invaded our gardens. Native to Europe and Asia, this insect first appeared in the United States in Cambridge, MA in 1980. It spread rapidly across the country and by 2003 it was well established in Colorado.

Paper wasps are social insects that live in nests constructed of individual papery cells. The nests usually hang downward and have open cells at the bottom. The European paper wasp is black in color with a series of yellow bands on its abdomen, which makes them look somewhat like yellowjackets. They are more slender than yellowjackets, however, and have exceptionally long hind legs that trail conspicuously when these insects fly.

The good news about the European paper wasp is that it feeds on live insects, especially caterpillars. During the summer months, I can go out into my vegetable garden and count at least five or six of these slender wasps patrolling over my cabbages, beans and tomatoes, searching for food. As a result, my cabbage plants have been free of cabbage looper larvae and my tomato plants are no longer victims of the voracious tomato hornworm caterpillars. These insects can strip a plant of most of its foliage overnight.

The bad news about the European paper wasp is that it eats all kinds of caterpillars. This aggressive hunter doesn’t discriminate between the “bad” caterpillars such as cabbage loopers and the “good” caterpillars such as the colorful larvae of the swallowtail butterflies that I once was able to rear on fennel and dill plants. Some experts have expressed concern that the presence of this aggressive wasp may cause a reduction in the number of colorful butterflies that grace our gardens and pollinate some flowers.

Another bad side of the European paper wasp is that it establishes nests in man-made objects. Favorite nesting sites include poles and children’s play equipment, building overhangs and crevasses in wooden decks. This puts the wasps in close contact with people and increases the risk of stings.

You can prevent nesting site establishment by sealing openings that allow access to hollow tubing. This should be done in mid-April when the wasps have just become active and are seeking places to nest. The interiors of many kinds of children’s play equipment such as swings are favorite nesting sites. Active nests can be destroyed with insecticide sprays. For best results, apply the spray during early morning or late evening when temperatures are low and the wasps are not flying. Effective insecticides include permethrin, tralomethrin, bifenthrin, tetramethrin, allethrin, and esfenvalerate. Many of these are combination products that include a fast-acting, short-lived ingredient (e.g., allethrin, tetramethrin) with an insecticide that is more persistent in its ability to control wasps (e.g., permethrin). Wasp traps, commonly sold in garden supply stores, are effective for yellowjackets but are not attractive to paper wasps.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  July 3, 2006