The adult moth is pale brown to grayish-brown in color, with a wingspread of about 40 mm. There is a characteristic white spot in the center of each forewing. The young larva is pale green . Like a cutworm, it may curl into a C-shaped ball when disturbed. All common lawn grasses are susceptible but are less likely to be attacked than corn, timothy, millet, small grains, and some legumes.
Older caterpillars begin feeding from the leaf edges and consume entire leaves.
Extensive feeding causes circular bare areas in lawns. Armyworms overwinter as partially grown, inactive larvae which resume feeding in early spring. Their habit of moving en masse from one area to another accounts for their common name. The first generation adults appear in May or June. They feed on nectar for several days, after which females begin laying eggs.