army worm Definition

any of numerous moths whose larvae travel in multitudes from field to field destroying grass, grain, and other crops; especially : the common armyworm (Pseudaletia unipuncta) of the eastern and central U.S. and Canada

an armyworm (Spodoptera exigua) that typically eats the foliage of beets, alfalfa, and vegetables

a migratory American noctuid moth (Spodoptera frugiperda) that is destructive to grains and grasses as a larva