Sod Webworms
Crambus spp.
Pediasia trisecta (Walker)
Tropical sod webworm, Herpeto gramma phaeopteralis Guenee


Adult -- The moths, 13 to 19 mm long, have a wingspan of about 15 to 35 mm. They have a prominent forward projection (labial palps) on the head. The forewings are brown or dull ash gray, with a whitish streak from the base to the margin; the hind wings are brownish. When at rest, the moths fold their wings in a tent-like manner over their body.

Egg -- The tiny, oblong eggs are white to pale yellow. Each egg is about 0.5 mm long and 0.3 mm wide.

Larva -- Most larvae vary from pinkish-white to yellowish to light brown. They are 16 to 28 mm long when fully grown, with thick bodies, coarse hairs, and paired dorsal and lateral spots on each segment. The head is yellowish- brown, brown, or black. Individual grubs often assume a C-shaped position. Tropical sod webworms are greenish and up to 19 mm long.

Pupa -- The reddish-brown pupae are 11 to 13 mm long.


Distribution -- Many species of sod webworms occur in the United States. The actual species present in any given area, however, is highly variable. Whereas many Crambus species are generally distributed, the tropical sod webworm is common primarily in Florida, and Pediasia trisecta abounds in Tennessee.

Host Plants -- Sod webworms feed on lawns, golf course grasses, some clovers, corn, tobacco, bluegrass, timothy, as well as pasture and field grasses. They usually favor bluegrass and Tifdwarf hybrid bermudagrass, but will attack most grasses.

Damage -- Larvae cut off grass blades just above the thatch line, pull them into their tunnels and eat them. The injury appears as small brown patches of closely cropped grass. If many larvae are present, the patches run together to form large, irregular brown patches.

Life History -- Webworms overwinter as young larvae a few centimeters below the soil line among the roots of weeds and grasses in silk-lined tubes. During early spring the larvae feed on the upper root systems, stems, and blades of grass. They build protective silken webs, usually on steep slopes and in sunny areas, where they feed and develop. In early May, they pupate in underground cocoons made of silk, bits of plants, and soil. About two weeks later, adults emerge. Beginning in May, moth flights may occur until October. The moths, erratic and weak flyers, live only a few days and feed solely on dew. They are active at dusk, resting near the ground in the grass during the day.

The eggs, which are deposited indiscriminately over the grass, hatch in 7 to 10 days. Young larvae immediately begin to feed and construct their silken tunnels. The most severe damage occurs in July and August when the grass is not growing rapidly. During this hot weather, the larvae feed at night or on cloudy days. Most sod webworms complete 2 or 3 generations each year, with approximately 6 weeks elapsing between egg deposition and adult emergence. In Florida, tropical sod webworms may produce a new generation every 5 to 6 weeks. A sod webworm infestation in the lawn can be detected by applying 1 tablespoon of pyrethrin (insecticide) in 1 gallon of water per square meter (or sq. yd.). The caterpillars will surface within a few minutes and can be found by separating the blades of grass, particularly at the interface between living and dead areas of turf. If 3 or 4 webworms are found in a 15 cm square (6 inch sq.) area, control is recommended.


Color plate -- sampling. For specific chemical control, consult state agricultural extension service recommendations.