Are earthworms good for your lawn?

Define "worm". If you mean earthworms, which are in Phylum Annelida, then the answer is a resounding "yes!". Earthworms decompose organic matter by eating decaying plants, and their feces (called "castings" in polite earthworm circles) is one of the best fertilizers in the world.

Earthworms also improve the soil by their digging and tunneling. Their movement turns over the soil, mixing nutrients . Their tunnels help water soak in and air get in too.

Other kinds of worms are not so good. Certain nematodes, which are smooth and frequently microscopic, can damage the roots of plants. Farmers spend lots of money trying to control this type of worm.