Answer: What you describe sound like sod webworms. Sod webworms are the caterpillars of lawn moths. The moths are small (1/2 inch long) and whitish-gray. They clasp or roll their wings close to their bodies when resting and have mouthparts projecting forward from the head like a snout. The moths are usually noticed when flushed out by a lawn mower or people walking. When disturbed, they fly in a jerky zig zag manner and quickly return to the grass to hide. Around dusk, they may be seen flying a few feet above the grass and dropping their eggs. In a few days, these eggs and others laid on the lower parts of the grass stems hatch into small caterpillars. It is the caterpillar that damages the grass.
The caterpillars generally have dark heads and rows of light-brown spots arranged in rings around the greenish-gray bodies. They live near the soil surface in silken shelters covered with bits of grass, essentially webbing the thatch into a mat. The larvae clip off grass blades close to the round and pull them back into their silken 'runways'. After several weeks of feeding, they reach maturity (now about 3/4 inch long), change into pupae (the resting stage), and soon emerge as moths. Two generations occur each year. The first generation adults appear in June and the second-generation adults in late July and August.
If this sounds like what might be invading your yard, you may be able to treat your lawn to reduce the population. For control, you can use the biological material Spinosad (sold as Conserve) or permethrin sold as Astro, or Bug Stop Concentrate).
Best wishes with your garden!
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