Bare circular areas in the grass are eaten to the ground. Green to dark-brown caterpillars with lengthwise stripes are present, moving in large numbers during the day. Armyworms and fall armyworms are the larvae of tan to gray moths that lay eggs in dry grass and thatch. Eggs hatch into light-green larvae that feed on grass blades. Larvae grow to 1 1/2 inches long, becoming darker as they mature. Armyworms eat any grass, including grassy weeds and lawns. They may appear suddenly and do a great deal of damage in a brief time.
To make lawns less attractive to armyworms, reduce thatch and eliminate soggy areas. Very large armyworms (1 1/2 inches) dig into the soil to pupate, and control may be difficult.