Q.Where does fertilization take place in earthworm?

Earthworm Reproduction

It would be a reasonable guess that an animal carrying both male and female reproductive organs in the same body could simply fertilise itself. The earthworm's actual reproductive behaviour deliberately avoids exactly this — and understanding why it still needs a partner is the key idea behind this topic.

Hermaphrodite, but not self-fertilising

The earthworm is hermaphrodite: each individual carries both testes (male organs, producing sperm) and ovaries (female organs, producing eggs) within the same body. But despite having both sexes' organs available, an earthworm still requires mating with another individual — it does not fertilise its own eggs with its own sperm.

What actually happens during mating

When two earthworms mate, they align themselves so their reproductive openings are in contact, and something distinctive happens: both partners exchange sperm simultaneously, each transferring sperm to the other through its own male genital opening. This means that during a single mating event, each worm acts as both a sperm donor and a sperm recipient at the same time — neither individual is playing only a "male" or only a "female" role, unlike in most animals with separate sexes.

Afterward, each earthworm uses the sperm it received from its partner — never its own sperm — to fertilise its own eggs. This mutual, cross-wise exchange is precisely what keeps the earthworm's reproduction genetically equivalent to cross-fertilisation in animals with separate sexes, even though a single individual physically carries both sets of organs.

What happens after fertilisation …