A species
Common earthworm
Lumbricus terrestris
Darwin's favourite soil engineers
You and the common earthworm last shared an ancestor about 580 million years ago (on 11 November, if life's history were one year).
Charles Darwin loved earthworms like this one. His final book, in 1881, was all about earthworms and the rich topsoil they make. They are soil engineers that plough for free: their tunnels let air and water into the ground, and their droppings help build soft, crumbly soil. Surprisingly, their cousins beside them on the tree include snails and clams.
It looks like a long, soft tube, reddish-brown at the head end and paler pink-grey towards the tail. Its body is made of many rings, with tiny bristles that grip the soil as it crawls. In adults, a smooth, pale saddle sits about one-third down from the head.
It digs a deep, lasting burrow that can reach down about 2 metres, deeper than most people are tall. It usually shelters inside by day and comes to the surface at night to feed on fallen leaves.
Both male and female
Each worm has both male and female parts but cannot fertilise itself. Two worms must pair up and swap sperm to make young.
A world traveller
It is native to Europe and now abundant in North America and western Asia.
Compost helper and fish bait
Earthworms help rot down garden compost heaps, and these large worms are used as live fishing bait. They stay common, and some farms even treat them as pests.