Earthworms feed on dead roots and stems and are usually an indication of fertile soil.
Although the earthworm may mar the appearance of the lawn, their activity improves the soil in several ways. Their beneficial movement from the surface to underlying soil helps mix the organic matter on the top with the soil below and reduces thatch accumulation. Their channels in the soil improve air and water movement through the soil. They even help improve the soil structure. Tolerating their presence and working at improving the lawn thickness and vigor will help mask their symptoms.