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 tube. Sod webworm pupae rarely are observed since they resemble a small clod of earth. In approximately one week, sod webworm adult moths emerge from their pupal case to mate and lay eggs.
Flights are most common shortly after dark.
The female moth flies low over the lawn area and scatters its eggs. Although adult moths have a short life span, usually less than two weeks, female moths 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. One common species of sod webworm, known as the cranberry girdler, feeds on grass roots rather than blades.