Earthworm Biology
Earthworm structure
An earthworm consists of a digestive tube housed within a thick cylindrical muscular tube that forms the body. The body is divided into segments, and furrows on the surface of the body mark the division between each segment.
The first segment encloses the mouth, and has a fleshy, muscular lobe on the top. This lobe can be pulled in to seal the mouth, or extended forward to probe the immediate surroundings. All segments, except the first, have eight retractable bristles which help the earthworm to grip surfaces as it moves.
Earthworm reproduction
Earthworms are hermaphrodites, meaning they have both male and female reproductive organs.
When two earthworms are ready to mate they adopt a head-to-tail position, cover themselves in a layer of mucus, and exchange sperm. The saddle produces a mucous tube which detaches and moves forward along the body, collecting on the way the earthworm’s own eggs and the sperm received from its partner.
Fertilization occurs in the mucous tube which is shed from the front end of the earthworm. This dries in the soil to become an egg capsule, from which one or more young earthworms will eventually hatch. Many species can reproduce several times a year.
Image left: Earthworms mating. Picture by Dr Kevin Butt, UCLAN, with thanks. Image right: Earthworm egg found in soil