Sod Webworms - "No it's not an internet virus"
The adult sod webworm is a small tan or buff coloured moth (1/4" to 3/4") that is commonly seen flitting about the lawn in short zigzag patterns. The moths lay eggs that hatch into larvae in a few days.
The larvae chew grass blade in two just above the ground level and pull the blades into a silken tunnel in the ground to eat them. Sod webworms chew and feed during the night and remain hidden in the daytime. They feed on the tender parts of the grass and as they grow, their appetites increase. Entire plants can be killed and irregular patches of dead grass will appear. The dead patches of grass pull away easily. Look at ground level for silk-lined tunnels, chewed grass, and frass (greenish, coarse, sawdust-like particles of excrement).
The larvae reach a mature length of about 3/4". They are a dingy, dull tannish brown but some are occasionally greenish. Frequently they have dark circular spots that are spaced along the sides and back. Stiff hairs protrude from these spots. The head is dark brown and shiny. When the larvae are finished feeding, they burrow into the soil or thatch to pupate. The larvae pupate for 10-14 days and then turn into the adult stage. The female adult lays eggs in late summer and the larvae develop in the fall.
The larvae overwinter in the tunnels. Adults emerge in May or June, laying eggs. Severe damage generally occurs in the fall as the population builds up. At that time control measures may be needed.