The pheretima posthuma is known as earth worm. It is found in the wet soil which is rich in organic matter. They belong to class oligochaeta. They are found in lawns, fields and gardens. They are nocturnal and omnivorous. The undigested food moves through the anus and forms heaps of pellets known as worm castings. They are fossorial. The circular and longitudinal muscles help in locomotion. They are hermaphrodite and protandrous. They show cross fertilization in the ootheca. They have great power of regeneration. Their head is made up of prostomium and peristomium. They have a clitellum which is found from 14 to 16 segments. Each segment has a curved and chitinous structure known as setae. The earthworm has multiple apertures like mouth, anus, male genital aperture, female genital aperture, spermathecal pores, dorsal pores and nephridiopores. The mouth comes inside the peristomium while the anus occurs in last segment. Female and male genital apertures are present on the ventral surface of 14 and 18 segments. The spermathecal pores are present on the different segments. The nephridiopores are present all over the body. They exclude first two segments. The dorsal pores are present on the mid dorsal line. There are multiple genital papillae present on the ventral side of 17 and 19 segments. The papilla resembles a cup which acts as a sucker. They make soil porous and light in weight. They also act as a source of manure. They increase the fertility and decrease the acidity and alkanity of soil. It acts as a food source for various animals and is also used to catch fishes. They may damage plants and can cause soil erosion by forming burrows. They also act as an intermediate host for certain parasites.