Sod webworms are the larvae of a tan moth that can be seen flying just above your lawn’s surface at dusk. Their larvae feed on grass blades near the soil, creating brown spots that expand as they grow. Since webworms feed at night and hide in the thatch by day, damage may go unnoticed. Look for tan moths on your lawn in the evening from May to midsummer, and contact your TruGreen specialist if you spot them.