Earthworms

There are 27 species of earthworm in the UK. Healthy farmland will have up to 1.75 million worms per acre.

We know they are the organic grower's best friends. These pages will help you to understand the different types, where they live, and what they do. As Darwin wrote "(There are few) animals which have played so important a part in the history of the world than the earthworm."

We also look at worm research - are worms affected by pesticides? How do they capture carbon, and how do they clean up contaminated soils.

And we hope you will take part in the great British Earthworm Survey! Earthworm Watch Your answers will increase our understanding of earthworm distribution, and how it is affected by the soil environment.

Why are earthworms important?

Organic growers love earthworms. Worms help create compost, they are food for the birds, and they are a natural way of improving the soil. They do this in three ways:

Improving soil structure Earthworms move through the soil creating burrows. This complex system of tunnels creates pores through which oxygen and water can enter and carbon dioxide leave the soil. Different types of earthworms make horizontal and vertical burrows, some of which can be very deep. A soil with plenty of worm burrows won't flash flood. But these burrows are not just a good drainage and ventilation system. They are lined with aerobic bacteria and digested leaf litter, bonded by mucus secreted by the worm, providing rich nutrients for plant roots.

Worm casts (waste matter) also help to create a fine crumb structure of soil. These casts can contain 5 times more nitrogen, 7 times more phosphorus and 1000 times more beneficial bacteria than the original soil.

Helping decomposition of organic matter Earthworms play an important role in breaking down organic matter. This includes decaying leaves and roots, animal manure, as well as any material found in the compost bin. Their decomposition releases nutrients, and makes them available for use by plants. The worm helps this process by eating the organic matter, breaking it down into smaller pieces and thus allowing bacteria and fungi to feed on it to release the nutrients.

Earthworms also mix soil layers and incorporate organic matter into the soil. Charles Darwin referred to earthworms as ‘nature’s ploughs’. This mixing improves the fertility of the soil, as the organic matter is dispersed and the nutrients become available to bacteria, fungi and plants.

Supporting bacteria and fungi Where earthworms are present, not only are there are more bacteria and fungi, they are more active. These minute life forms release nutrients from organic matter, and are an important source of food in their own right for the many other animals that live in soils. (Link to Kate’s piece on soil microfauna.)

More about earthworms ….

There are three types of worms:

  1. Anecic earthworms are the most common earthworms in the UK. They are the largest species, often reddish brown, and they 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, as often seen in grass. They make middens (piles of casts) around the entrance to their burrows

  2. Endogeic earthworms are pale coloured - pink, grey, green or blue - and make horizontal burrows through the soil to move around and to feed. Some can burrow very deeply in the soil.

  3. Epigeic earthworms don't make burrows, but live on the surface of the soil – often in leaf litter and in compost. They rapidly consume the compost material, and reproduce very quickly. They are usually bright red or reddish-brown, and the compost worms in particular (known as brandling or tiger worms) are often stripy.

To help you identify worms in your garden, you can buy an excellent earthworm guide from the Field Studies Council. Here also is a full list of UK earthworm species.

And here is the latest report of earthworm presence throughout the UK.

By the way, contrary to popular belief, it is not true that cutting a worm in half will result in the regeneration of two separate worms.

Further reading

Visit the Earthworm Society of Britain See their helpful FAQs, which include “How do I tell one end of worm from the other?” and “Why do worms come out after rain?”

Download this simple fact sheet on worms.

Watch these BBC videos on earthworms and this one which shows how the blackbird uses vibrations to tempt the worm out of the soil.

Further Research

Do worms help with carbon capture? This article explains how scientists in the US and China discovered that worms, though they release carbon dioxide from the soil into the air, actually capture (sequester) more CO2 than they release.

Are worms affected by pesticides? In short, yes. Not only can the toxic chemicals increase worm mortality, but also they affect the worms' health, functioning ability and fertility. See also this research paper which looks at the impact of glyphosate on worms.

How do earthworms deal with soil contamination? They combine the metals, such as lead and zinc, with phosphorus or sulphur in special 'compartments' in their cells. This locks the metals into tiny pellets that come out in the worms' poo. This paper reveals that worms which live in highly toxic soils have evolved to accumulate more pollutants in their tissues than those that live in cleaner soils. This article explains the process .

Charles Darwin was fascinated by worms. His book, The Formation of Vegetable Mould through the Action of Worms, with Observations of their Habits, sold 6000 copies in its first year, selling faster than On the Origin of Species when it was first published. His studies revealed that earthworms are indifferent to noise, but sensitive to vibrations – in a curious experiment involving a grand piano. Worms beside the piano didn't move, despite loud playing, but those on top were agitated by the vibrations.