Forest tent caterpillars expected to invade Minnesota

Forest tent caterpillars are expected to invade Minnesota in droves the next couple of years.

The native insects stripped the leaves off about a million acres of hardwood trees across the state last year and in the next year or two their numbers will likely peak, Minnesota Department of Natural Resources officials say.

Afterwards, the caterpillar population will fall dramatically before slowly starting to build again, a cycle that repeats about every 10 years.

Caterpillars don't harm healthy trees, but they do create a nuisance, said Mike Albers, a forest health specialist for the department.

"They can be smelly," he said. "When you run over them on the road, they can get on your car and tires."

Their cocoons also stick to houses, and their digested waste drops from trees. During the last peak in 2001-2002, about eight million acres of forest were defoliated, mostly in northeastern Minnesota.

Last year, caterpillars did more damage in the state's north central and western forests. Albers said the bugs munch leaves through May and mid-June, but trees typically refoliate by July.