• The forest tent caterpillar is a native defoliator of a wide variety of hardwood trees and shrubs. It is often mistakenly called the armyworm.
• Its range in North America extends from coast to coast and from the tree line in Canada to the southern states. Caterpillars feed primarily on aspen and birch trees in northern Minnesota and on basswood and oaks farther south.
• Northern Minnesota outbreaks occur in five- to 10-year intervals and last five to eight years. In the last 120 years, outbreaks peaked in 1891, 1898, 1912, 1922, 1937, 1952, 1967, 1978, 1990 and 2001.
• During outbreaks, forest tent caterpillars can number from 1 million to 4 million per acre. Large, mature caterpillars often crawl across roads and open areas in search of food. Resting caterpillars form large clusters of thousands of caterpillars on buildings, tree stems, cars, campers and other stationary objects.
• Forest tent caterpillar eggs are extremely hardy and easily survive Minnesota winters. The caterpillars spin cocoons in early to late June, and adult moths emerge seven to 10 days later.
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• The moths that eventually hatch can migrate hundreds of miles and trigger new outbreaks.
• Tent caterpillar populations eventually collapse from starvation when their numbers exceed available foliage. Starvation typically kills 75 percent to 95 percent of the caterpillars.
• Another significant natural control occurs near the end of the outbreak cycle when a parasitic native fly kills many pupae in their cocoons.
• More info: dnr.state.mn.us/treecare/forest_health/ftc/index.html
