Partially grown larvae overwinter in soil. Feeding by larvae resumes in the spring as soon as temperatures warm when they do most of their damage. Larvae have a wide host range, damaging grain, alfalfa, sugarbeets, and other vegetable and grass crops. Army cutworm larvae measure about 1.5 to 2 inches in length when they have completed this stage in their development at which time they burrow out a chamber in the soil for pupation. Adult moths emerge from the soil in May and June feeding on nectar-producing flowers before beginning their long distance migration to the mountains.
Adults migrate to high elevations and form aggregations where they spend the summer.
Recent research has indicated that the pale western and army cutworms may play an important role in the grizzly bear diet with estimates as high as 14,000 moths consumed per bear per day. As temperatures cool and day length shortens the moths fly back to Plains, mate and lay eggs. A pheromone trapping program has been used to detect their movement back to agricultural areas. Moths are attracted to areas with loose, recently tilled soil to deposit eggs. Eggs are the overwintering stage of this insect, waiting until spring to hatch.