When temperatures rise in spring, the caterpillars resume feeding and become full grown in May and early June. Most lawn injury occurs during this time. The sod webworm caterpillars then change to the pupal stage within the silken tubes. Because they resemble a small clod of earth, sod webworm pupae rarely are observed. In approximately one week, adult moths emerge from their pupal cases to mate and lay eggs.
Flights are most common shortly after dark.
The female moth flies low over the lawn area and scatters her eggs. Adult moths have a short life span, usually less than two weeks. Females can lay up to 60 eggs per evening. Sod webworms have one to two generations per year in Colorado. When a second generation occurs, peak larval feeding and damage is in July.