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Dead Wasps in Winter

February 10, 2017
picture of dead paper wasps

photo credit: John Obermeyer

In the dead of winter, we occasionally have to pick up dead wasps around our house. The wasps are often found on the carpet in the basement. But not always. Sometimes a dead wasp is on the windowsill, other times in a light fixture. To be sure, dying wasps can also be observed crawling around lethargically or even attempting to fly.

Most people know these insects as paper wasps. This is because the wasps use chewed wood mixed with saliva to produce a paper-like product known as “carton.” Paper wasps use carton as building material to fashion the structure of their nests. The same material is also used in the honeycomb-like structures where the wasps raise their young. These wasps are sometimes called vespids because they are classified in the genus Vespula.

So why do we find paper wasps in the house in winter? Here is the story. Like a lot of social insects, paper wasps survive subfreezing winter temperatures by hibernating as adults. But not just any adults. The hibernating adult wasps are mated females. All other wasps in the nest die when winter sets in.

Many other species of social Hymenoptera, including bumble bees, bald-faced hornets and yellow jackets also spend the winter as mated queens. In general the system works this way: In late spring, a mated queen comes out of hibernation as temperatures begin to warm. Such a queen is known as a “foundress,” the individual that starts a nest.

After emerging from her long winter’s nap, the foundress begins to fly around, looking for a nest site. A bumble bee or yellow jacket foundress will look for an underground site, such as an abandoned rodent burrow. Some bumble bee queens will start a nest between hay bales stacked in a barn. A bald-faced hornet foundress will look for a limb on a tree as a place to attach a nest. Paper wasps generally establish a nest in a protected location, such as under the eves of a house or barn.

Once a wasp or bee foundress finds a nest location, she has a lot of work to do. She must start constructing the nest, and in the case of paper wasps, that means chewing up wood to produce the carton building material. Like the little red hen of children’s book fame, she has to do all the work by herself. This is because a startup nest has no workers in the beginning. So the foundress starts building a nest, fashions a few cells in the comb, lays an egg in each cell, and begins collecting food for her larvae once they hatch. The food for paper wasp larvae is chewed up insects.

Once the larvae in the paper wasp nest complete their development, they transform into the pupal stage before emerging as adult insects. These new wasps, called workers, take over the job of collecting materials to expand the nest. They also gather food and feed their developing siblings. The workers become the protectors of their home, and almost anyone who has deliberately or accidently disturbed a paper wasp nest can attest to this fact.

As the seasons progress, more and more wasps are produced and the size of the nest structure grows. As the fall season approaches, the wasp colony shifts from producing workers to producing male and queen wasps. Once these wasps become adults, the females mate and fly away from the home nest in search of a protected place to spend the upcoming winter months.

This brings us back to the paper wasps wandering around my basement during the winter months. These are likely female wasps that decided to spend the winter in a fireplace chimney of our house. We didn’t use that fireplace this winter, but the winter sun often warms the interior of the chimney to springlike temperatures. Over time, a consistently warm chimney environment will send a false signal to the hibernating wasps that summer is on the way. The wasps break out of hibernation and make their way down the chimney and through the fireplace into the house.

The house temperature was warm enough to keep the wasps alive, but there was no food available, and they ended up starving to death. I guess that is a good thing. For sure I would not be a happy camper if a queen paper wasp started building a nest inside the house.

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