armyworm

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A caterpillar belonging to either of two genera of moth, Pseudaletia or Spodoptera, large groups of which destroy crops and other vegetation.

Century Dictionary and Cyclopedia

1. n. A name given to the larva of Leucania unipuncta (Harris) on account of the immense numbers in which it sometimes marches over a country, completely stripping it of all the grasses and young grain in its way. It undergoes transformation in the ground. The parent moth has a conspicuous white dot on the disk of the front wings.

Wiktionary

1. n. The larva of various species of noctuid moth, which typically feed in large, destructive groups

GNU Webster's 1913

1. A lepidopterous insect, which in the larval state often travels in great multitudes from field to field, destroying grass, grain, and other crops. The common army worm of the northern United States is the noctuid moth (Pseudaletia unipuncta, formerly Leucania unipuncta. The name is often applied to other related species, as the cotton worm.
2. The larva of a small two-winged fly (Sciara), which marches in large companies, in regular order. See cotton worm, under cotton.
3. the larva of the fungus gnat; -- they march in large companies in regular order.

WordNet 3.0

1. n. noctuid moth larvae that travel in multitudes destroying especially grass and grain
2. n. noctuid moth larvae that travel in multitudes destroying especially grass and grain
3. n. larva of fungus gnat that feed on cereals and other grains; they march in large companies in regular order when the food is exhausted
4. n. moth whose destructive larvae travel in multitudes