The name "armyworm" has been applied to the forest tent caterpillar and other moths whose numbers buildup, defoliate trees, and then move in great numbers to other trees to continue their leaf damage. The true armyworm, Pseudaletia unipuncta, is a caterpillar that belongs to the cutworm family, and it is primarily a pest of grasses, small grains, and corn. Only rarely does it feed on tree leaves.
Great numbers of the adult moths reach our state on strong southerly winds, they lay eggs here and the armyworms have started their seasonal invasion. A large population of this pest was found in central Minnesota July 29th east of Brainerd destroying grasses and small grain plants. Several reports of this pest destroying grasses, small grains, and corn in southern Minnesota have also been received by the Department of Agriculture. This insect does not overwinter in great numbers in Minnesota because nearly all of the second generation of caterpillars are killed by our fall frosts.
Armyworms grow to one and one-half to two inches and vary in color from a light gray-green to almost black. Along the outer side of each leg, near the middle part of the body, is a dark band. A series of longitudinal stripes are arranged on the body as follows. l. A thin, unpaired, white, broken line down the middle of the back. 2. A wide, dark, mottled stripe halfway down the side. 3. Next, a pale orange stripe with white border followed by a brownish, mottled stripe. 4. And another pale orange stripe slightly above the legs. Adult moths are heavy bodied, light brown, and each front wing has a white or silvery spot about the size of a pinhead.