Several different moths with similar habits are called sod webworms or lawn moths. These night-flying moths drop eggs into the grass as they fly. The eggs hatch into worms that feed on grass blades at night or on cloudy, rainy days. In the daytime the worm hides in white silky tubes in the soil. Sometimes an entire lawn is killed in a few days.
Rake out all the dead grass, mow the lawn, and water thoroughly before treating. Damaged lawns may recover rapidly if the insects are controlled early.