Earthworms play a vital role in breaking down organic particles in soil and aerating soil, and their waste, called castings, is used by gardeners as fertilizer. They also play a role as bait in fly fishing.
Earthworms spend most of their time underground, where they eat the soil as they burrow. They get energy and nutrients from fragments of decaying leaves and other organic matter. Earthworms use tiny stones in their gizzards to grind up the soil and any food particles completely. The chemical and physical processes that the soil goes through in their digestive systems makes the nutrients in the soil much more accessible to plants.