Proteins, sugar, starch, and amino acids are the fresh organic molecules which is part of the soil which defines how the soil is healthy or good soil. You can find that these earthworms live off of by eating the soil itself and by their cast / secretions they also in return help to fertile the soil although by a very miniscule fraction. The actual benefit of the soil from the earthworms would be that it is able to aerate the soil and cultivate tunnels for water to be able to seep through the layers of the soil.
