Beneficial Bugs: Earthworms.
From the time we are kids, we are told that worms are good for the garden and soil, but we rarely are ever told why. Earthworms can eat their weight in decaying plant matter every day. That thick band you see toward one end of their bodies is the area that holds their reproductive organs. Two worms become impregnated by each other and offspring can live for 10-12 years.
Earthworm castings (excrement) greatly improve the texture and mineral content of the soil. They are high in phosphorus, nitrogen and potassium, all minerals many soils would lack without these soil dwellers.
To encourage worms in your garden, make sure to add plenty of compost to keep them in your garden soil. If they do not have organic matter in the soil to feed on, they will go elsewhere.