Earthworms can be grouped into categories by their morphology, ecology and vertical position in (or above) the soil. We call these groupings ecotypes, and they can be useful for studying earthworms.
Earthworms in the ecosystem
In the UK, we group earthworms into 4 ecotypes:
Anecic earthworms make permanent vertical burrows in soil. They feed on leaves on the soil surface that they drag into their burrows. They also cast on the surface, and these casts can quite often be seen in grasslands. They also make middens (piles of casts) around the entrance to their burrows. Anecic species are the largest species of earthworms in the UK. They are darkly coloured at the head end (red or brown) and have paler tails.
Anecic earthworm species include Aporrectodea longa, Aporrectodea nocturna, Lumbricus friendi and Lumbricus terrestris.
Endogeic earthworms live in and feed on the soil. They make horizontal burrows through the soil to move around and to feed and they will reuse these burrows to a certain extent. Endogeic earthworms are often pale colours, grey, pale pink, green or blue. Some can burrow very deeply in the soil.
Endogeic earthworm species include Allolobophora chlorotica, Apporectodea caliginosa, Apporectodea icterica, Apporectodea rosea, Murchieona muldali, Octolasion cyaneum and Octolasion lacteum
Epigeic earthworms live on the surface of the soil in leaf litter. These species tend not to make burrows but live in and feed on the leaf litter. Epigeic earthworms are also often bright red or reddy-brown, but they are not stripy.
Epigeic earthworm speices include Dendrobaena octaedra, Dendrobaena attemsi, Dendrodrilus rubidus, Eiseniella tetraedra, Heliodrilus oculatus, Lumbricus rubellus, Lumbricus castaneus, Lumbricus festivus, Lumbricus friendi, Satchellius mammalis
As their name would suggest, these are most likely to be found in compost, or areas very rich in rotting vegetation. They prefer warm and moist environments with a ready supply of fresh compost material. They can very rapidly consume this material and also reproduce very quickly. Compost earthworms tend to be bright red in colour and stripy- some people call the stripy species 'tiger worms'. Compost worms are often used to help dispose of waste as they can also remove contaminants from soil.
Compost earthworm species include Eisenia fetida and Dendrobaena veneta
Want to learn more about earthworm ecology?
In reality, earthworm ecotypes are a bit more complex than the four categories we've outlined above. Keiron Derek Brown discusses the earthworm ecotypes in more detail in this FSC Virtual Meetup. Find out how to tell the different groups apart and how earthworms may not neatly conform to the four ecotypes.