While mammals are shivering through a record cold and snowy winter, the insect world is faring better.

Some of the most notorious pests – like ticks, black flies and browntail moth caterpillars – seem to have acclimated well to harsh winters and deep snow, which acts like a thick blanket insulating many of those bugs from the frigid air, experts say.

“This really cold weather we’ve had, it would really be nasty to overwintering insects, but unfortunately, most of them are 3 feet under, fat and happy sitting in the duff on the ground there well-insulated,” said Jim Dill, pest management specialist with the University of Maine.

The duff is the thin layer of leafy, organic material just beneath the surface of the ground, which is itself insulating, where many insects spend the winter months.

Bare ground, along with prolonged cold, can kill some pests.

“Just after Christmas, it was green grass almost, and it got cold for a while. I don’t think the cold was around long enough. It was two to three days and then the snow started moving in,” Dill said. “If the snow wasn’t here, it would be a really good winter for taking out some insects.”


The cold weather could affect insects that winter just under the bark or in the cracks of trees, like yellowjackets and bald-faced hornets.

“They may have been exposed to this really, really cold winter,” Dill said, but added that those insects find so many places to winter that there will still be plenty come spring.

Browntail moths that overwinter in tightly woven webs at the end of branches are open to the elements, but they are well adapted to the cold.

The hemlock wooly adelgid, an invasive species from Japan that stresses and can kill hemlock trees, is sensitive to cold but at least some will likely survive. Last winter, in some of the state agriculture department’s samples, 80 percent died.

“That meant 20 percent remained,” said Allison Kanoti, forest entomologist with the Maine Department of Agriculture, Conservation and Forestry. “Those remaining may be more resistant to cold temperatures and may pass that on to their offspring.”

But knocking the population down at least gives the trees a reprieve to regain strength and better withstand future infestations, she said.


The cold weather and early snows in November are likely to have taken out many winter moths. The adult males fly in late November to December and are susceptible to early chills, Kanoti said. That could lead to less defoliation in coastal towns from Kittery to Rockland, where the moths are well-established.

Ticks, however, aren’t suffering.

“There’s so much snow out there insulating them, they aren’t going to be exposed to the very low temperatures that would be needed to do anything to their life cycle,” said Dr. Peter W. Rand, senior investigator at the Maine Medical Center Research Institute’s vector-borne disease laboratory.

The research team is participating in a study to determine the impact of overwintering on ticks. All three stages of the arachnids’ life cycle – larvae, nymph and adult – can be found beneath the leaf litter.

Black flies winter as larvae in aquatic environments where they also are shielded from the most severe cold.

Generally, cold winters are bad for insect mortality if the conditions are right, said Andrei Alyokhin, professor of applied entomology at the University of Maine in Orono. While much of this winter has been accompanied by heavy snow, there were stretches in December where cold weather hit with almost bare ground.

Alyokhin said insect activity will probably be less in the spring and summer than if the winter had been warm, but that also means a decrease in beneficial insects.

“Beneficial bugs will also decline so there’s less of them to control pest bugs,” he said. Also, they are an important food source for fish, birds, mammals and species such as salamanders.

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