why earthworm is called the friend of farmer ?

Explanation

Earthworms are called friends of farmer because they make burrows in the soil and make it porous which helps plants in respiration and penetration within helps plants plants in respiration and penetration within the soil
the worm casting is rich in urea and ammonia which improves fertility fo soil , thus they are of much importance to mankind and used ammonia which improves fertility of soil thus they are of much importance to mankind and used as vermicompart.