The European Paper-Wasp:
A New Threat to Cavity-nesting Birds Is Coming!
This article was originally published in the Purple Martin Update 9:12(2000). Used with permission of the author and the Purple Martin Conservation Association. © 2000 by the Purple Martin Conservation Association. All rights reserved.
Eugene S. Morton
Conservation and Research Center
National Zoological Park
1500 Remount Road
Front Royal, VA 22630
Click on a photo for an enlargement
A new exotic importation, the European Paper-wasp (Polistes dominulus) is spreading. First recorded in Cambridge, Massachusetts, in 1980, it spread quickly to nearby towns in the Boston area. It has since been recorded in New Jersey (1986), Pennsylvania and upstate New York (1991), northern Ohio (1991), Connecticut (1993), and Vermont (1994). It is rapidly spreading across the lower part of Michigan and, in 1995, was spotted at an Interstate 95 rest stop in Maryland, just north of Laurel, and also in a small shopping center in Biddeford, Maine. And, like the gentle encouragement people gave the European House Sparrow in the early years of its U.S. invasion, the first Michigan record of the European Paper-wasp was collected carefully, at night, "to minimize any threat to the survival of the newly-discovered colony." Deja vu?
The nest of the nonnative European Paper-wasp (Polistes dominulus) shown here inside a plastic SuperGourd that has been cut in half for the photo. The author found this wasp nest and hundreds of others placed inside bird houses, tree tubes, hollow ladders, and sheds, in northwestern Pennsylvania.
You can identify a paper-wasp by its thin waspy waist and the paper nest, which usually hangs downward and has open cells on the bottom. The nests are common under eaves and inside outbuildings. No mud is found in paper-wasp nests. The hornets and yellowjackets have thicker bodies and build domes of paper enclosing the cells where the young are raised, which often take on the classic "football" shape of cartoon fame. The European Paper- wasp is colored black and yellow like a yellowjacket and is slightly smaller than our native brown and tan Common Paper-wasp (Polistes fuscatus). A good picture of the wasp and its nest can be found at <http://www.news.cornell.edu/releases/Aug98/WaspQueen.bpf.html>.
The European Paper-wasp, unlike our native Common Paper-wasp that also sometimes uses bird boxes, is bad news. The European prefers to nest in cavities and it attacks people with much less provocation than the native paper-wasp. My first encounter with it occurred in 1996 in northwestern Pennsylvania near Brown Hill at the Hemlock Hill Biological Research Area in Crawford County. Plastic tree tubes, five feet high, had been placed around small oaks to protect them from deer browsing. I peered into the top of one and found myself eyeing a paper-wasp nest one foot down the tube. Immediately, wasps flew up at me and I instinctively jumped back. They did not follow me very far, but I was surprised at the rapid attack. That's odd, I thought, paper-wasps do not attack unless really provoked. Gingerly, I looked at the nest and thought they might be a forest species of paper-wasp, unfamiliar to me, that found the tree tubes adjacent to the forest just a dandy new forest environment. Paper-wasps, in my experience, were usually around human abodes, not out here in the middle of a field near the woods.
A European Paper-wasp nest attached under the lid of a wooden bluebird box in the author's Pennsylvania yard.
I queried a Smithsonian colleague, Karl Krombein, at the National Museum of Natural History, and first learned that this was the European Paper-wasp, not a native species as I had assumed. The European Paper-wasp is native from the Mediterranean region to China. The next year, 1997, the European wasps colonized my house and garage, usurping colonies from the native paper-wasp. My first sting occurred when I was winching down my Troyer 14-unit Martin House to remove the latest starling nesting attempt. The wasps were nesting under the predator guard. The heavy wooden house plummeted down as a wasp stung my cheek and I jumped backwards, releasing the handle. Ouch! (The Troyer house caught on the safety bolt through the pole after dropping 10 feet - it was not destroyed!). My second sting occurred two weeks later as I scaled an aluminum ladder to check a starling box trap. I had left the ladder up against the garage where the trap was attached to facilitate frequent attention to trapped starlings. The ladder's rungs were hollow and everyone of them but the lowest was housing the beginnings of a European Paper-wasp nest! I had provided them, inadvertently, with a perfect nesting site. I now lay the ladder flat and check it for nests frequently.
The European Paper-wasp prefers cavities for its nests and will build on a vertical surface as well as, for example, inside the top of a nest box. I found several nests in hawthorn shrubs when browsing by deer makes their crowns thick and dark. The native paper-wasps usually begin a new nest each year. One result is that the colony does not become very large. The European Paper-wasps, which, like all paper-wasps, overwinter as queens, often stay on the nest all winter and use it the next year and so on. Due to this head start, the colonies become larger than those of the native paper-wasps do. I now wear gloves and have a spray can handy whenever I check nest boxes. Checking nest boxes is no longer the pleasant task it once was because the European Paper-wasp may have staked a claim in them. One box I cleaned contained the stick nest of a House Wren and 34 overwintering queen European Paper-wasps in the bottom under the wren's twigs. Fortunately, this was on a cool October morning and I was wearing leather gloves. I found only one SuperGourd, out of the 12 I have, occupied by the wasp and only one nest in a Trio Castle compartment. Because I have been unsuccessful in attracting martins, nothing can be said about possible direct effects of the new wasp on martin colonies or their establishment. I am planning two studies, one to document the percentage of nest boxes colonized by the new European wasp invader and the other to determine whether or not they deter birds from using a box. In my mind there is no doubt that they will deter birds. We are initiating a paper-wasp study in nest boxes at the Conservation and Research Center, Front Royal, Virginia. Here, the European Paper-wasp is still unknown. There are also many government vehicles parked at the Conservation and Research Center, in various stages of repair. These are ideal nesting sites for the new wasp. Indeed, nesting sites described in a publication on the European Paper-wasp in the Boston area were "sheds, garages, abandoned trucks, or field station houses." (Nonacs and Reeve, 1995, The ecology of cooperation in wasps: causes and consequences of alternative reproductive decisions. Ecology 76(3):953-967).
On the plus side, paper-wasps help gardeners by removing cabbage butterfly larvae from the broccoli. Nobody knows if they will affect the success of butterfly gardens by eating all the caterpillars, but few monarch larvae survive the native paper-wasp foragers in my experience. The addition of a voracious new paper-wasp that prefers sheltered nesting sites mostly around human habitations does not look good for butterflies in these areas. Please let me know if you encounter the European Paper-wasp and take data on its occurrence in bird boxes. We need to know how much of a pest this latest exotic invader might become.
Dr. Eugene S. Morton is a senior scientist at the Smithsonion Institution in Washington, DC. He is also a scientific advisor to the PMCA (Purple Martin Conservation Association). He is well-known for his landmark work with Purple Martin downsong and on DNA fingerprinting in martins.
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