They help to break down and condition plant remnants in their gut. Earthworms may be viewed as pests because their burrows and castings create a roughened surface. Also, since earthworms are a preferred food for moles, pesticides are sometimes applied in an effort to remove food so that the moles will go elsewhere. There is no scientific evidence that elimination of earthworms will reduce problems with moles.
Earthworms make significant contributions to a fertile, healthy soil.
Attempts to control them to reduce surface disruption can have severe consequences, especially in thatch build up. Thatch is a layer of living and dead roots, stems, and organic matter that accumulates at the soil surface. Thatch accumulates when the rate of decomposition is much lower than the rate of grass growth. Excessive thatch reduces penetration of water and other materials, such as fertilizer. It also encourages shallow grass roots which makes turf more susceptible to stress and pests.