What is an earthworm?

The term ‘Earthworm’ is a collective name for a group of organisms within the class Oligochaeta which means 'few bristles'. Oligochaeta is a class in the phylum Annelida which means ‘little ring’, these little rings refers to segments found on all Annelids. Earthworms are distinguished from other groups of Oligochaeta by their ecology.

Earthworms are predominantly terrestrial, though they can be found in some freshwater environments such soils of river banks and at the bottom of lakes. Earthworms are found on all continents. Earthworms need a moist environment due to their method of respiration, as they diffuse oxygen and carbon dioxide through their skin. Their skin produces a film of mucous for the process to occur, and therefore has to be moist for respiration to take place.

An Earthworm has a long segmented body, which has a mouth at one end and an anus at the other. The mouth is closer to the clitellum, which is commonly called the saddle, found around a third of the way down the body. An earthworm moves via a line of bristles called setae, which can be found in pairs on each segment.

To find more out about the biology of an earthworm please visit our Earthworm Biology page.

If I cut an earthworm in two will it grow into two earthworms?

Garden spade

Unfortunately not, if cut behind their clitellum (saddle) they may regrow a tail. However the tail which has been cut from the body will die. This is because the brain and the main part of their respiratory system is located between the head and clitellum.

Earthworms are very numerous, so a few lost when digging in the garden won't make a big difference, but at ESB we'd always encourage people to be kind to earthworms and not do it on purpose!

How do I know which end of an earthworm is which?

The earthworms head is closer to its clitellum (saddle). An earthworm also moves forward with its head first, so it is always worth looking at which direction it is moving in, particularly if it is a juvenile and does not have a clitellum (saddle). 

If you look closely you will be able to see an earthworm’s mouth, which is on the second segment of a worm known as the peristomium. This is used along with the first segment the prostomium to help us identify the species of earthworm.

To find more out about the features of an earthworm please visit our Earthworm Identification page.

How do you tell the species of earthworms apart?

Emma Sherlock's FSC AIDGAP key to earthworm species in the UK

You can identify an earthworm by looking at a number of external features, such as the head, male pour and clitellum. Because earthworms are small you need a microscope and an identification guide. If you are looking a UK species there is a key to the 27 different species of earthworms. 

To buy the UK and Ireland Earthworm Identification Guide please visit the Field Studies Council Publications page.

If you are interested in identifying and recording earthworms please visit our Earthworm Recording Scheme pages

Why do earthworms come out when it rains?

It is not fully understood why earthworms come up to the surface when it rains, though there are a few theories. The theory with the most evidence is that earthworms find it easier to move across the soil surface when it is wet, to find food, new habitats or a mate.

When the rain hits the ground it creates vibrations on the soil surface.  This causes earthworms to come out of their burrows to the surface. Earthworms find it easier to travel across the surface of the soil when it is wet, as they need a moist environment to survive.

Birds exploit this behaviour by mimicking rain hitting the ground by drumming their feet to encourage the earthworms to the surface to feed on them.

What do earthworms eat?

Earthworms eat a range of matter. In Earthworms, by Sims and Gerard (1985), most earthworms are described as omnivorous (eating plants and animals).  However they better described as detritivores (eating decaying plant and animal matter).

Since then the study of earthworms has shown that they may be preferential fungivores (eating fungi). There are studies to suggest they eat a fungus called mycorrhiza which grows on the roots of some plants. Some species have also been described as geophagous (soil eating).


In the UK there are four different ecotypes, they show the diversity of different feeding niches:

  • Composting earthworms feed on decaying plant matter and manure that is near the start of the decomposition process.
  • Epigeic earthworms live in leaf litter and rotting logs and feed on organic matter that is partially decayed.
  • Anecic earthworms pull decaying plant matter in to their burrows.
  • Endogeics earthworms eat soil which is high in organic matter.

To find out more about different Earthworm ecotypes please look at our Earthworm Ecology page.

Can you help me with my earthworm project?

The Earthworm Society of Britain’s main objective is to record earthworms. We are always happy to hear from anyone who wishes to study and further theirs and our knowledge of earthworms.

The Earthworm Society of Britain is run by volunteers, therefore our time is limited however please send us an email and we can answer your question or put you in the direction of someone who can help. 

Please send all enquiries to info@earthwormsoc.org.uk,thank you.