Sod Webworm

Sod webworm is a general name applied to the larvae of several small moths in the family Crambidae, a group often called "lawn moths" or "snout moths" because the adults hold long labial palps forward like a beak. The caterpillars are turf-feeding insects found throughout lawns, athletic fields, golf courses, and pastures across North America, where they can produce circular patches of thinned or browning grass during warm months.

The larvae spend their lives at the soil surface, spinning loose silk tunnels among grass crowns and thatch. They feed nocturnally on grass blades and can be locally abundant, especially in dry, sunny, well-drained turf. Because the caterpillars are small, cryptically colored, and stay hidden in silk retreats during the day, they are far more often noticed by their feeding damage than by direct observation.

• Body dull gray, tan, or greenish with rows of small dark spots (pinacula) bearing short bristles running down each segment
• Head capsule dark brown to black, contrasting with the paler body
• Length at maturity roughly 0.5-1 inch (12-25 mm); body tapers slightly at both ends
• Larvae curl into a tight C-shape when disturbed
• Found inside loosely woven silk tubes at the thatch/soil interface, often mixed with bits of chewed grass and frass
• Adult moths are small, buff or straw-colored, and fold their wings tightly along the body at rest, giving a narrow, tube-like silhouette

Sod webworms live in residential lawns, parks, golf courses, sports fields, and grassy pastures wherever turfgrasses such as bluegrass, fescue, bermudagrass, and zoysiagrass grow. They are most numerous in sunny, well-drained areas with a buildup of thatch, which provides shelter for their silk tunnels. The insects occur widely across temperate and warm-temperate North America, with activity concentrated from late spring through early fall depending on the region and number of generations.

Larvae are nocturnal grazers that emerge from their silken burrows after dark to clip grass blades near the crown, then drag the cut pieces back into the tunnel to feed. During the day they remain hidden, making infestations easy to overlook until circular or irregular patches of stunted, brown turf appear. As decomposers of plant material and prey for birds, ants, parasitic wasps, and predatory ground beetles, sod webworm larvae play a modest role in turf ecosystems, cycling grass tissue and supporting insectivorous wildlife despite being regarded as a lawn pest.

Adult moths lay tiny eggs on grass blades in early summer. Newly hatched larvae construct silk-lined tunnels at the soil surface and pass through several instars while feeding on grass over a period of weeks. Mature larvae pupate within the silk tunnel or a nearby soil chamber. Depending on climate, sod webworms typically complete one to three generations per year, and in colder regions the partly grown larvae overwinter in the thatch before resuming feeding and completing development the following spring.