European Paper Wasps (Polistes dominula) look like a cross between a yellowjacket and a paper wasp. They have the body size and shape of our native paper wasps, but the black and yellow markings of yellowjackets. They are paper wasps clad in yellowjacket clothing and if their nests are threatened, they have the disposition of a baldfaced hornet.
The native range of European paper wasps extends throughout Europe and North Africa east into China. The wasps were first reported to have found their way into North America in a 1981 paper describing nests near Boston, Massachusetts, although the authors identified them as P. gallicus which is another similar-looking European native. Since that time, P. dominula has spread across the U.S. and Canada.
On the other hand, the wasp's capricious population densities in Ohio have been puzzling over the past several years. After becoming the dominant paper wasp during the 2000s, they all but disappeared in the 2010s. The population downturn was not observed in other states such as Kentucky, but more on that later.
The reason for the dramatic population decline of European paper wasps in Ohio is not known. However, it appears they are now making a dramatic comeback and their odd nesting habits can put them in conflict with people.
The European paper wasps present two challenges. They nest in unusual places increasing stinging risks to people. They also decimate monarch butterfly (Danaus plexippus) caterpillars reducing the impact of monarch habitat restoration.
Sneaky Nesters
The nests of our native paper wasps are found out in the open but protected from the weather by being located under roof overhangs, or inside open structures such as attics and outbuildings. They are easy to spot as long as you look up!
However, European paper wasps are sneaky nesters. They commonly build nests in locations where we generally don't find native paper wasps, such as in dense shrubbery, inside railings and mailboxes, and inside the bases of light poles. These nesting locations may bring them into stinging conflicts with people.
Paper wasp stings are painful. However, stings by European paper wasps are even more painful because research has shown a correlation between their conspicuous warning coloration (aposematism) and the volume of their poison gland.
I almost experienced this first-hand last week while checking some shrubs for winter damage. I parted the stems on one of the shrubs and exposed a European paper wasp nest with several sets of compound eyes looking back at me. I gently moved the foliage back into place and backed away. Then I regathered my composure, carefully re-parted the stems, and took pictures.
It is believed the European paper wasp's secretive nesting behavior provides protection from predators. The scientific literature notes this may partially account for their rapid success in exploiting new territories perhaps at the expense of our native paper wasps..
Toppling Monarchs
European paper wasps present an ecological conundrum. Like their North American counterparts, these wasps provide a beneficial twofer. They are frequent visitors to flowers, so they are considered pollinators.
They are also predators and forage for meat in the form of caterpillars and sawfly larvae to feed their young. Thus, their predaceous lifestyle may be viewed as beneficial in landscape pest management programs.
However, European paper wasps are such highly aggressive meat-eaters they will forage on a much wider range of insects compared to our native paper wasps. The wider meat market available to these non-native wasps has been cited as another reason they have been so successful in displacing native wasps.
Another downside to the European paper wasp’s voracious appetite is that they readily spirit away monarch butterfly caterpillars. This Jekyll and Hyde lifestyle is well documented in a paper published in 2020 by scientists at the University of Kentucky (see Selected References below). The title of their paper summarizes the impact: “Invasive paper wasp turns urban pollinator gardens into ecological traps for monarch butterfly larvae.”
The researchers found that European paper wasps were most successful targeting early to middle instar monarch butterfly caterpillars. The wasps had a more difficult time handling full-sized caterpillars with their ability to mount a defense by violently thrashing around and/or dropping from the plants. Indeed, early instar caterpillars would also occasionally successfully escape the wasp’s jaws of doom by dropping from plants, but there was a cost. It disrupted their feeding which affected their development.
One of the more intriguing problems highlighted in the paper is the result of unintended consequences. The researchers connected the European paper wasp's monarch-munching behavior with their tendency to nest in unusual locations.
In this case, it was nesting inside so-called butterfly “hibernation boxes.” The researchers found that 16 out of 22 boxes located in pollinator conservation gardens on the University of Kentucky’s campus contained wasp nests with 13 being European paper wasps.
It’s been well-documented that “hibernation boxes” do not serve as safe havens for butterflies; they don’t use them. However, they can serve as boxes of doom for monarch caterpillars … they bring the wolves to the sheep.
Selected References
Hathaway, M.A., 1981. Polistes gallicus in Massachusetts (Hymenoptera: Vespidae). Psyche: A Journal of Entomology, 88(1-2), pp.169-173.
Vidal-Cordero, J.M., G. Moreno-Rueda, A. López-Orta, C. Marfil-Daza, J.L. Ros-Santaella, and F.J. Ortiz-Sánchez. 2012. Brighter-colored paper wasps (Polistes dominula) have larger poison glands. Frontiers in Zoology, 9(1), pp.1-5.
Baker, A.M. and D.A. Potter. 2020. Invasive paper wasp turns urban pollinator gardens into ecological traps for monarch butterfly larvae. Scientific Reports, 10(1), pp.1-7.