Why Are There Green Caterpillars in My Yard?

Several varieties of green caterpillars appear in your landscape for a number of reasons. Some attack the leaves on shrubs, trees and flowering plants, while others concentrate on lawn grass. The most common type lawn caterpillar is the sod webworm. Rather than a single variety of insect, this term encompasses more than 20 different caterpillars that eventually turn into moths.

The little green caterpillars in your lawn are moth larvae. Common webworm varieties in your lawn include Parapediasia teterrella, Chrysoteuchia topiaria and Agriphila vulgivagella. Most varieties are smaller than an inch in length and have dark spots running down their bodies. Although they vary slightly in size, shade of green and color pattern, they all feed on grass blades, often causing extensive damage.

Sod webworms appear after the mother moths lay the eggs near the base of the grass blades. The larvae hatch and crawl underground. They spend the winter several inches below the surface of the soil. In the spring, the small caterpillars emerge near the blades of grass in your lawn and begin feeding on the new growth. At the end of their larval stage, usually after four to six weeks, the caterpillars go back beneath the soil, where they then pupate. Adult moths emerge after about two weeks, mate and lay eggs, beginning a new cycle.

Grass is one of sodworms' main food sources. These crawling lawn pests prefer feeding on turfgrass, although they eat whatever food is available. Common food sources for these caterpillars include perennial ryegrass, tall fescue, fine fescue and Kentucky bluegrass. Their constant feeding habit causes small, brown patches of grass that may run together. Underground tunneling damages grass roots, leading to a general thinning of the lawn.

An unhealthy lawn sustains greater damage from sod webworms than do lawns in good condition. Water, fertilize and mow your lawn regularly, according to the variety of grass. Nematodes, such as Steinernema nematodes, help reduce the sod webworm population. Contact pesticides applied during late summer or fall help eradicate these caterpillar pests. Planting a resistant type of grass also reduces the possibility of sod webworm damage. Look for seed grass packages that are endophyte enhanced when planting new grass seed.