Earth worms, as they cultivate and feed, swallow great quantities of soil, digest it, extract its food value and expel the residue as worm castings. These worm castings are 5 times richer in the nutrients necessary for maximum plant growth and production than the soil they ingested.
Just as important, these worms, commonly known as 'red wigglers' and technically known as Eisenia fetida, are one of the most effective agents for loosening and aerating the soil. Their tunnels are lined with earth worm castings and allow oxygen to reach plant roots. Also, as the earthworms burrow, they create channels which increase the capacity for the soil to hold water. In soil where earth worms have been introduced, there are more nutrients and oxygen available for roots, softer soil for improved root growth, and better water retention.
It is always helpful for the worms to add compost to the soil since they are constantly looking for organic material to eat and convert to castings. Almost any kind of plant waste or food waste can be either put directly into the soil or broken down first in a compost pile or container and then added to the soil. This will significantly increase worm reproduction and speed up soil improvement.