DOMINULUS OR EUROPEAN PAPER WASPS

Polistes dominulus, Vespidae

P. dominulus is frequently mistaken for a yellowjacket. Smaller than the native northern paper wasp, the dominulus paper wasp (Fig. 1) is yellow and black, resembling the pattern (especially on the abdomen) of the yellowjackets in the genus Vespula.

As in all paper wasps, the “waist” is very thin. During flight, the hind pair of legs trail below in an extended fashion. The nest is the characteristic upside-down umbrella shape, and the open cells can be seen from below. Cream-colored larvae are legless and remain within their cells until they emerge as adult wasps.

A highly successful colonizer, this wasp has rapidly increased its distribution in the United States during the past 20 years. Before the introduction of this new species, the northern paper wasp, Polistes fuscatus, was the most frequently encountered species in and around structures in Pennsylvania.

P. dominulus was first discovered near Boston, in Cambridge, Massachusetts, during the late 1970s. Since then, the wasp has been recorded from Maine, Vermont, Connecticut, New York, New Jersey, Maryland, Pennsylvania, Ohio, and Michigan. It has recently been discovered in California and Washington.

Fertilized queens from the previous year begin new colonies of P. dominulus each spring. These queens overwinter in protected areas such as under the bark of dead trees, in hollow trees, within wall voids of houses, under siding and occasionally within the cells of a paper wasp nest. Although most nests are newly constructed each year, the queens will sometimes use a previous year’s nest, thereby establishing their colonies earlier in the season than our native species.

The queen deposits small, elongated eggs (one to a cell) that hatch in several days. She will feed her young larvae masticated caterpillars and other insects. In contrast, our native species of Polistes prey only on caterpillars. After the first brood of larvae mature and emerge as worker females, the queen will limit her activity to laying eggs to expand the number of workers. The workers assume the duties of food collection, nest construction, and colony defense. With optimal temperatures and a plentiful food source, the larvae complete their development and become adult wasps in as little as 40 days.

Nests are constructed in protected locations such as under and within the eaves of structures, in attics and wall voids, and in many other enclosed areas. Some of the more notable locations where nests have been encountered include exterior lighting fixtures, parking meters, animal skulls, bird boxes, and infrequently used equipment like gas grills, motor homes, boats, and autos.

Speculations for the rapid expansion of the dominulus paper wasp include:

• Earlier seasonal establishment of colonies allowing P. dominulus to establish workers before our native species, thereby benefiting foraging activities and colony expansion; (Note: This behavior can expose them to late-season freezes from which they might not survive.)
• Avoidance of native bird predators by early nest establishment. Early establishment provides the nest with more workers to protect the larvae;
• Use of numerous enclosed nest sites, providing protection from predation;
• A more varied diet (many different genera of insects in several orders) benefits early and rapid larval development.

Dominulus paper wasps are very attentive to potential threats to their nests. They can detect movement at 12 to 20 feet from the nest but fortunately do not typically attack unless people are very close (inches away). However, since they prefer to hide their nests within voids and other enclosures, this behavior increases the risk for unpleasant encounters. An unsuspecting homeowner may be stung, for instance, while attempting to change a lightbulb for an outside fixture, or while painting or removing window shutters. Furthermore, observations in Pennsylvania indicate that these wasps are extremely common in urban settings.

Whenever new species are introduced into an environment (either intentionally or accidentally), there are unpredictable consequences. The increased risk for stings is an obvious concern. Even more troubling, it appears that this new introduction has had an adverse impact on the native species of Polistes. The apparent reduction of indigenous Polistes will undoubtedly result in a change in the faunal balance. It is unclear what the consequences will be. Some entomologists worry that the large numbers of P. dominulus will adversely affect the species of desirable insects (i.e., butterflies).

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