The name army worm is generally applied to the larvae of certain types of Lepidoptera that sometimes migrate to new feeding grounds in large armies, destroying corn, small grains, sugar cane, cotton and other crops as they move. The moths deposit their eggs on the underside of grass leaves and when the larvae hatch they grow slowly, eating small amounts of leaf tissue and causing little, if any, damage. But when they enter their last larval stage, they exhibit tremendous appetites and it is during this phase, which usually lasts 10 days, that farm crops in an area of several hundred square miles can be destroyed.