Moths flying in lawn
Sod webworms are a complex of over 20 species of Pyralid moths across the U.S. Two species that have occurred in outbreak situations are the bluegrass webworm and the larger sod webworm. The caterpillars are the damaging stage of these moths. Caterpillars range in size from ½ to about an inch long (depending on the species) when fully grown. The larvae vary in color from greenish to beige, brown or gray. Most of the caterpillars have dark circular spots scattered over the body.
Sod webworms feed on the grass blades. They spin silk threads as they move through the grass, webbing leaves and soil particles together. They often form horizontal silk tubes in the thatch. Most of the noticeable feeding damage occurs from mid-July through the end of September in Maryland. The caterpillars feed at night consuming the green grass blades, leaving the thatch visible the next morning. The damage resembles severe scalping by a lawn mower.
Reseed damaged areas with grasses with high levels of endophytes, such as tall fescue. Bt (Bacillus thuringiensis) a biological insecticide can be used to control young larvae.
Adapted from: "Sod Webworms". Lee Hellman and J. Kevin Mathias, Institute of Applied Agriculture, University of Maryland, College Park, MD.