Common Earthworm

• fisiologíaIt has no lungs and breathes through its damp skin, so it can drown if it stays under standing water too long.
• reproducciónIt is hermaphrodite, with both male and female organs in the same animal, though it generally needs to mate with another to fertilise its eggs.
• Darwin calculated that a population of earthworms moves some 100 tonnes of soil per hectare per year; he devoted his last book, published in 1881, to them.
• It breathes through its skin, which it needs to keep moist: if dawn catches it outside its tunnel, it dies of dehydration.
• Along the Atlantic fringe of north-west Europe it is locally threatened by predation from the New Zealand flatworm (Arthurdendyus triangulatus), an invasive species.
• This is Darwin's earthworm. He devoted his final book to it, published in 1881, and calculated that the earthworms of an English field turned over some twenty tonnes of soil per hectare each year, a revolutionary idea at the time: that the entire soil passes through the gut of earthworms.
• It is anecic, meaning it digs permanent vertical burrows and comes to the surface at night to drag leaves down inside. That mixing of plant material with the deep mineral layer is what creates fertile soil.
• It is a hermaphrodite, and mates on the surface, joined to another worm by the clitellum, exchanging sperm in both directions.
• Here is the twist: in North America it is a serious invasive species. The northern forests, which evolved without earthworms after the last glaciation, depend on a thick layer of undecomposed leaf litter, and these worms consume it within a few years, altering the soil, the vegetation and the fauna.
• It spreads above all through discarded fishing bait and the movement of soil and plants.
• Its scientific name is misleading: terrestris does not mean it is the only terrestrial one, but alludes to its relationship with the soil.

Skeleton type

Invertebrate - no skeleton; the body is supported by a hydrostatic skeleton (annelid)

Habitat & environment

Damp soils rich in organic matter, preferably clay. It digs vertical tunnels that can be more than 2 m deep and into which it drags leaves from the surface

Litter / clutch size

A cross-fertilising hermaphrodite; the eggs gather in the clitellum, the thickened band between segments 31 and 37, before being laid

Lifespan in captivity

About 6 years

Sources consulted: Asturnatura; Wikipedia (Lumbricus terrestris); Biopedia; CABI (ficha de especie introducida); Darwin 1881, The Formation of Vegetable Mould through the Action of Worms

Best time: Damp nights and rainy days, when it comes to the surface to feed and mate