A break in a brick wall makes the perfect place for Polistes to build their nest. Photo credit: Paula Shrewsbury, UMD
In a previous episode we met the dashing common paper wasp, Polistes exclamans, and learned of its beneficial role as a hunter of caterpillars, nefarious foliage consumers of our trees, shrubs, and garden plants. On a recent excursion along the scenic Gunpowder River in Baltimore County, MD, I had the pleasure to meet one of P. exclamans’ close relatives which I believe to be either P. metricus or its newly named cousin P. parametricus. These two paper wasps are so closely related that only experts far more erudite than this Bug Guy can differentiate between them. No matter exactly who these fierce and fascinating wasps are, the tidbit I share this week involved encounters with these curious wasps. While cycling along the scenic Northern Central Railroad trail, I stopped on a long-abandoned trestle overlooking a bucolic scene of river, forests, and farms. To prevent swooning runners or wayward cyclists from falling off this trestle, a tarnished metal railing stood guard. From a hole beneath one horizontal bar of the railing dozens of busy paper wasps issued forth from their tubular refuge. The perfectly circular opening, obviously designed to accommodate a missing 3/8 inch screw, became the choke point for workers leaving and returning to the nest. Passage in and out was often accompanied by testy encounters by nest-mates lingering near the entrance.
A bit later in the ride, I happened across yet another wasp nest. This one occupied an unseen void behind the brick wall of a building. A vertical inch long section of missing mortar between two bricks was the entrance to the nest. Hanging out near the portal was a fidgety gang of wasps checking out workers returning from food-gathering forays. Upon returning to the nest, one hapless wasp was jumped by this mob, pinned to the surface of the brick, and roughed-up for more than a minute by her nest-mates.
A petulant mob of hungry paper wasps lies in ambush at the opening of a nest. A hapless worker returning to the nest is grabbed and robbed of her groceries as she attempts to enter. In the end she finally breaks free and escapes.
Now, we all know that wasps and bees are famous for their social behaviors that involve gathering food, defending the nest, attending the queen, and caring for the young. So what’s up with this rather unsocial behavior? To understand, let’s look at the seasonal dynamics of a typical paper wasp colony. Each nest is initiated in spring by a female wasp called a foundress, a lucky wasp that survived the wicked winter in a sheltered spot, perhaps beneath the bark of a tree or a behind a loose piece of siding on a home. In spring, the foundress uses her powerful jaws to gather wood fiber from trees and shrubs. She chews it into pulp and molds the pulp into papery cells. After the first few cells are constructed, the foundress deposits an egg within each chamber. Eggs soon hatch into legless larvae. Her youngsters have healthy appetites and the queen gets busy hunting food for her babes. Caterpillars are one of the favorite menu items and in this way paper wasps are our allies in the fight against these leaf-munching garden pests. After subduing its prey, the paper wasp uses its jaws to slice and dice the victim into a spongy ball. The caterpillar ball is transported back to the nest where hungry mouths await. A high protein diet of fresh caterpillar meat helps small wasp larvae grow rapidly.
Not all potential foundresses are successful in establishing a colony. Some may join an established nest where they assist the resident foundress in caring for brood. These subordinates forgo their right to produce young of their own. If some do attempt to lay eggs in the nest, the dominant foundress will find her competitor’s eggs and eat them. Tyranny rules the paper wasp nest! The colony grows as summer progresses and in some species more than a hundred workers may be produced. With the approach of autumn, production in the colony shifts from making workers to making future foundresses and their mates. The new queens and kings that emerge from their cells are a rather lazy lot and spend little time helping with the care of the colony. As workers return to the colony with food for developing larvae, the petulant royals waylay the workers, steal their provisions, and eat meals intended for young. With the waning of autumn, the colony declines as fewer workers are produced and less food arrives to for those that remain. Famed sociobiologist E.O. Wilson describes some species of paper wasps engaging in “‘abortive” behavior at season’s end where larvae are not only starved by hungry adults but are also pulled from their cells and eaten. Yikes! But in the meadow, paper wasps continue to provide the important ecosystem service of pollination. If you go to the meadow, enjoy them on many of our late season bloomers like goldenrod, boneset, and sedum.
The gentler side of paper wasps is seen as they gather nectar and help pollinate autumn bloomers like goldenrod.
Acknowledgements
Two marvelous references, “The Insect Societies” by E.O. Wilson and “Biological studies of Polistes in North Carolina (Hymenoptera: Vespidae)” by R.L. Rabb, and the Maryland Biodiversity Project were used in the preparation of this episode. Thanks to Dr. Shrewsbury for providing inspiration and photography for this episode.