Armyworm is a caterpillar especially harmful to corn and other grains, and garden crops east of the Rocky Mountains in the United States and Canada. It is the larva (young) of a night-flying moth (see Larva). Sometimes, large numbers of these caterpillars march like an army across fields. They stick together in dense patches and sometimes form processions 12 or 14 feet (3.7 or 4.3 meters) long and 2 or 3 inches (5 or 8 centimeters) wide. They apparently band together to search for new feeding grounds.
The armyworm is hairless and fleshy. It is about 11/2 inches (3.8 centimeters) long, and has green and yellow stripes. When full grown, it burrows into the soil and transforms into a pupa (see Pupa). The pupa changes into a pale brown moth that emerges in the spring. The female moth deposits strings of eggs on the lower leaves of grasses. The caterpillars hatch from these eggs. They usually feed at night and hide during the day. There are two or three broods per year.
Farmers fight armyworms with various insecticide sprays. Dust furrows (narrow grooves) may be dug as barriers against them. The natural enemies of the armyworm include parasitic flies and wasps, and the fiery ground beetle.
