Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

2/16/04

Contacts:
Laura Jesse, Entomology, (515) 294-7400, lrahnsen@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Garden Column for the week of Feb. 20, 2004

Social Wasps in Iowa

By Laura Jesse
Graduate Assistant
Iowa State University Department of Entomology

Although it may insects, especially wasps, are probably not what leaps to mind when you think of love and romance. I know what you are thinking, "Wasps?" You see, wasps belong to a group of insects called Hymenoptera. Hymenoptera is derived from Hyman, the Greek god of commitment and marriage. So it seems only fitting to spend a little time this month thinking about the wonderful array of wasps we have here in Iowa, and consider the possibility of a new invasive wasp making its way here.

There are three major groups of social wasps in Iowa: hornets, yellowjackets and paper wasps. They live in colonies that consist of workers, which forage for food, and a queen, which is the only member of the colony that can reproduce. Each colony constructs a nest by combining wood fibers with saliva to make a paper-like substance. This is shaped into a nest that is particular to each type of wasp. Social wasp colonies only last for one year and a new nest must be built each year. The only member of the colony that over-winters is the fertilized queen, all of the workers die with the first frosts.

Hornets are beneficial predators that feed on other insects, particularly filth flies and blow flies. They build large, round paper nests that are attached to tree branches and found primarily in wooded areas, although they can found near human dwellings as well. The nest is composed of three or four tiers of combs housed within a thick, multilayered outer shell. A single opening at the bottom allows the hornets to fly in and out. Peak worker population is about 100 to 400 hornets by the end of the summer. Baldfaced hornets are the most common species here in Iowa. They are large, black insects about 7/8 of an inch long with white to cream-colored markings on the front of the head and at the end of the abdomen.

Yellowjackets are foragers who prefer the same types of food we do - carbonated beverages, fruits and vegetables, candy, ice cream and meat. They build paper nests similar to those built by hornets, except that yellowjackets place their nests underground or in a hollow log or landscape timber - even within the walls or attic of a house. Yellowjacket nests may contain as many as 5,000 workers by the end of the season. This is they can become a nuisance as their colonies have large numbers of foraging workers that can be found around garbage cans and unlucky picnickers. A yellowjacket worker is about 1/2-inch long with a relatively short and blocky body shape and a black and yellow-striped abdomen.

Paper wasps are foragers that prefer to feed on caterpillars. They build the familiar umbrella shaped nests often found hanging from eaves, window frames, porch ceilings or attic rafters. These nests consist of a single tier of hexagonal cells suspended by a short stem with no external covering. The northern paper wasp is a common species in Iowa. Northern paper wasp adults are about 3/4 to 1 inch long, reddish-orange to dark brown or black in color, and have two orange, eye-like dots on their abdomen. Their colonies normally contain fewer than 25 wasps, but late in the season of a good year, their numbers may swell to more than 100.

There may be a new species of paper wasp making its home in Iowa in the near future - the European paper wasp. The European paper wasp, Polistes dominulus, was first reported in Massachusetts in 1981 and populations have now reached the Midwest. The European paper wasp is somewhat smaller than the northern paper wasp and is black with bright, yellow stripes and spots. While they are closely related to our native paper wasps, the prospect of their arrival is of concern for several reasons. First, they may be able to displace our native paper wasps. Second, European paper wasps tend to locate their nests where humans are more likely to come into contact with them. Finally, the effects of their feeding on caterpillars and other insects are unknown.

European paper wasps have several competitive advantages over our native paper wasps. They have a shorter generation time, meaning they can produce more individuals in the same amount of time. They establish their colonies earlier in the year, giving them a significant head start. They also spend less time and energy building nests, sometimes even resorting to reusing an abandoned nest. They do not use as much saliva in the construction of their nests as our native paper wasps do. This is important because the saliva acts as waterproofing for the nest. European paper wasps, therefore, need to build their nests in very protected areas where waterproofing is not so critical. Unfortunately, most waterproof places are man-made. This brings European paper wasps into more urban areas than our native paper wasps. Their nests have been reported inside bird boxes, parking meters, outdoor light fixtures and gas grills. Although we have not yet confirmed this species in Iowa, its presence in nearby states means it will likely be found here soon.

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Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 152K. Caption: A paper wasp nest

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