Worms in yards often eat grass clippings, but they rarely eat grass while it is still growing. Worms occasionally leave small mounds called worm castings that can damage lawns. This damage is the result of concentrated nutrients in the worm castings burning nearby grass.
Worms are sometimes used to speed up composting in a process called vermiculture. In vermiculture, feeding grass clippings to worms is not recommended, because the clippings are likely to contain pesticides and fertilizers that interfere with the composting process. Grass clippings also tend to reach high temperatures while decomposing, which kills off worms and other beneficial bacteria.