The worm is the gardener's best friend. Night and day worms are burrowing through acres of soil, swallowing soil as they go. Inside the soil are tiny bits of plants and animals which they then grind up as they eat. Earthworms actually eat the soil. Through the process of digestion, nutrients that are locked up and unavailable are released in their waste called castings.
Worm castings are characteristic lumps and bumps of soil that come out as part of the worms waste.
Rich in nutrients such as nitrogen, potassium, and phosphorus, worm castings help plants to grow. The average earthworm will produce its weight in casting every 24 hours. One earthworm can digest several tons of soil in one year. Not only do castings add nutrients to the soil, but they also improve the soil's ability to hold water, another bonus for plants. By tunneling through the soil, worms aerate the soil, providing a looser structure and openings for roots to grow.