University of Illinois Extension

Insects' Winter Plans

Cold temperatures send some outdoor insects looking for a warm home, said a University of Illinois Extension horticulture specialist.

“Late fall and winter is a period when most outdoor insects go dormant, just like our trees and shrubs,” said Richard Hentschel. “Insects can overwinter as adults, huddled together or by themselves in cracks and crevices or in leaf litter, hoping to avoid extremes in temperatures.

“Other insects overwinter in a cocoon rather than as adults; still others overwinter as eggs above the soil in leaf litter or in bark crevices or below ground. Any protection, no matter how they overwinter, affords them a better chance of winter survival unless they are very hardy.”

Insects like yellow jackets and hornets find a place to hide underneath the bark of trees and sit out the winter by themselves. This is in contrast to box elder bugs that gather in enormous numbers. Most of the lady beetles overwinter in numbers at the base of trees and shrubs by the hundreds.

“A very well known garden pest, the tomato hornworm, overwinters in vegetable garden debris as a cocoon,” he noted. “Earwigs can be found in leaf litter and in bark crevices all summer long, yet overwinter as an egg in the soil.

“Some of our tree-boring pests overwinter as larvae or pupae just underneath the bark in the cambium layer. This is the case for the recently discovered emerald ash borer in the northeastern part of Illinois.”

Why do we have box elder bugs all winter in our homes? As the weather turns cool and then cold, the Box Elder bugs seek out warm shelter and find their way into our outer home walls through existing cracks and crevices for the winter, Hentschel explained.

“Remember, they are dormant, not dead, so as heat continues to escape into our walls from inside, the box elder bugs are naturally drawn to the heat and find their way to the interior of the home,” he said.

In the fall, when all manner of outdoor insects are looking for a place to overwinter, using a foundation spray outdoors will keep a great many of those crawling insects at bay, he added.

“Those that make it inside can be vacuumed up while they are moving about,” he said. “Many insects cannot survive indoors without their natural food sources and are often drawn to a window. They can be removed from the window sill once dead.”