Forest tent caterpillar damage rising as DNR eyes potential 2027 outbreak

AITKIN — Tree damage from forest tent caterpillars is on the rise in Minnesota.

The Department of Natural Resources reported the caterpillars have damaged the leaves of 60,000 acres of foliage in Aitkin County and surrounding counties in 2026 so far, according to a Thursday, Aug. 6 news release.

In all of 2025, the caterpillars damaged 41,200 acres.

Forest tent caterpillars are also known as “armyworms,” though the DNR clarified that true armyworms area different species that favors crops and grasses. Forest tent caterpillars — which are becoming more common in Northern Minnesota — feed on tree leaves.

Leaf damage from the caterpillars will not automatically kill the plant, according to the DNR. However, continuous periods of feeding can cause bare and dead limbs, called dieback. The damage can also prove too much for trees weakened by factors like drought and disease.

Staff at the DNR said periods of extreme forest tent caterpillar damage, called outbreaks, occur every 10 to 15 years.

The most recent outbreak in 2013, which the DNR stated was considered “generally very light,” consumed a million acres. The most recent large outbreak occurred in 2001, when the caterpillars chewed through 7.7 million mapped acres.

“We are currently in that 10 to 15-year window for another large outbreak,” the DNR stated. “Only time will tell if another intense, massive outbreak develops like it did from 2000 to 2003, but we do expect even more defoliation in 2027.”