Minnesota's native forest tent caterpillar populations go into outbreak mode every 10 to 16 years.

Last year, the population increased from 2012 and resulted in the defoliation of 1.3 million acres. Based on historic trends, we should be expecting two to four million acres of defoliation this year, but on 38 of 39 egg mass survey plots this spring, DNR staff found only one or two egg masses or none at all - although on one plot near Tower in St. Louis County, there were enough egg masses to defoliate the plot trees six times over.

From these results, it's difficult to predict what will happen with FTC populations and the impacts they will have this summer. Time will tell.

The forest tent caterpillar, Malacosoma disstria, is a native defoliator of a wide variety of hardwood trees and shrubs and can be found throughout the range of all hardwood forests in North America.

FTCs primarily feed on aspen birch basswood oak.

FTCs are often mistakenly called army worms. Defoliation from FTC causes little damage. A second set of leaves will develop by mid-July. There are natural control mechanisms that will cause populations to collapse.

FTCs are native insects and play critical roles in structuring aspen mixed-wood forests and helping to improve forest dynamics.

Life cycle

  • Caterpillar: The forest tent caterpillar is colorful, with many hairs. The sides of its body are blue with narrow orange stripes, and the back is black with footprint or keyhole-shaped white markings.
  • Newly hatched caterpillars are black with obvious hairs and are about ⅛-inch long. Mature caterpillars are 2 to 2½ inches in length.
  • Egg Masses: Eggs are laid in masses wrapped around the twigs of trees and shrubs in late June to mid-July. New egg masses are ½-inch long and covered with glossy, dark brown, glue-like material that protects the eggs during winter. They blend in with the tree, and look like a swollen spot on a twig from a distance.
  • Moth (Adult): The adult moth is tan and has a broad brown band across the front wings. FTC moths are night fliers and are attracted to lights in large numbers