Earthworms move in the soil, which makes the soil loose, and air and water can penetrate into the soil more deeply, which is beneficial to plant growth and can improve the soil.

Earthworms contribute to material circulation and energy transfer in soil process by feeding, digesting, excreting (earthworm dung), secreting (mucus) and digging holes. They are one of the soil invertebrates (mainly earthworms, mites and ants) that have an important influence on many processes that determine soil fertility, and are called "ecosystem engineers".

Morphogenesis

The body is segmented without division, the wart foot degenerates, and the body surface has bristles. Androgyny, with 1-2 pairs of gonads, the reproductive duct originated from the body cavity. When sexually mature, there is an annular band on the body surface, which can fertilize each other during mating. Eggs are produced in the girdle, and form cocoon after shedding, which develops directly.

The setae are solitary, 8, sometimes many, arranged in a ring shape, with 1-2 pairs of testis, usually at10-1node, and a pair of male reproductive pores, which are located on two or more somites behind the posterior testis, namely/kloc-0. A pair of ovaries, located at 13, have thick bands and few yolk.

Earthworms have been identified by karyotype analysis in China. Chromosome 2n=22 of Eisenia foetida is exactly the same as that of artificially raised earthworms "Taiping II" and "Beixing II".