Earthworm  (Lumbricus terrestris)

The importance of earthworms in the aeration and fertilisation of the soil is well known. They bring organic matter down into their burrows from the surface, and the familiar 'worm casts' consist of soil excreted by earthworms (3). Charles Darwin estimated that the population of earthworms moved 100 tonnes of soil per hectare in a year (5). Oxygen is taken in across the surface of the body, and the skin has to be kept moist to facilitate this process; earthworms only venture to the surface after rain or at night for this reason (3).

All earthworms are hermaphrodites, meaning that a single individual possesses both male and female reproductive organs, but self-fertilisation does not occur. On damp days in summer, earthworms surface in order to mate. During copulation, two individuals lie side by side, with their 'head' ends overlapping. The overlapping parts of their bodies become surrounded by a single mucous tube, which holds them closely together. They simultaneously secrete sperm, which passes along a groove in the body of each worm and enters a small sac in the partner. After mating, the worms separate, and the saddle begins to secrete a mucous cylinder into which eggs and sperm are released. The worm wriggles out of the cylinder, which then closes, forming a protective cocoon in which fertilisation and development of the eggs take place (3).

Earthworms have been used for bait by anglers, and are an important food source for many species of mammals and birds. They have been used in folk medicine as a remedy for stomach problems and toothache (5). Contrary to popular belief, it is not true that cutting a worm in half will result in the regeneration of two seperate worms (4).