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Organic compost and diverse gardens are best for the UK’s earthworms
One of the largest investigations into UK earthworms has revealed how we can all support the vital work of these creatures.
With help from thousands of community scientists across the country, researchers have found that worms prefer gardens with a mixture of vegetable beds, shrubs and lawn.
Making our gardens earthworm friendly could help urban spaces become more resilient.
Between 2016 and 2018, people living across the UK took part in Earthworm Watch, a community science project aiming to understand life beneath our feet.
The results are now in, revealing that earthworm-friendly practices, like having a mixture of habitats in back gardens, helps boost the diversity of the worms living there.
In turn, these worms can help to bury carbon and improve the drainage of soils, enabling our towns and cities to adapt to floods and other extreme weather.
Dr Victoria Burton is a Natural History Museum researcher who specialises in studying soil life, and was the lead author of the new research.
“This paper offers some clues about how to manage our spaces better for earthworms, and ourselves,” Victoria says. “For example, we found that inorganic fertilisers didn’t cause an increase in earthworms, but organic composts did.”
“Disturbing our soils less also seems to be important, with no-dig methods of garden management perhaps helping to encourage earthworms. Leaving dead leaves in place, rather than taking them away to compost separately, will also provide additional food for these worms and other organisms.”
The findings of the study were published in the European Journal of Soil Biology.
You're most likely to see an anecic earthworm like Lumbricus terrestris at night, when they come to the surface to feed. Image © Liz Weber / Shutterstock.
What do earthworms do?
Earthworms are a vital part of our planet’s ecosystems. They’re decomposers – a group of animals and other organisms that break down dead matter and release the nutrients back into the wider world.
It’s just one of the many ways these invisible invertebrates help to keep our soils healthy. Earthworms bury organic material and move it deeper into the soil, where it breaks down more slowly. This allows the ground beneath our feet to lock up carbon for longer and prevent it from entering the atmosphere.
The worms’ burrows are also important for drainage. By opening up gaps in the soil, water can penetrate deeper into the ground, making it less likely to build up and flood areas on the surface.
Not all earthworms are created equal, however. As well as there being more than 30 species in the UK, earthworms in this country also have a lifestyle that falls into one of three broad categories.
“Worms are divided into three ecotypes, groupings that represent a worm’s lifestyle,” Victoria explains. “It’s often difficult to identify worm species without a microscope, so these are helpful to use in the field. They’re all important in plant litter recycling, just in different ways.”
Endogeic earthworms are those which feed on the soil itself and create horizontal burrows beneath the surface. These pale-coloured worms, which include species like Octolasion cyaneum, are generally fond of soils containing chalk or clay, and rarely come to the surface.
Epigeic earthworms like Eisenia fetida, meanwhile, are small, red-coloured animals which dwell on the surface of the soil. These short-lived worms make their home in rotting leaf litter, helping to break it down.
Anecic earthworms like Lumbricus terrestris also feed on leaf litter, but generally only come to the surface at night. As the largest and longest-lived of the UK’s earthworms, they can dig vertical burrows which extend several metres underground.
While the roles of all earthworms are important, the fact that they live beneath our feet means they tend to be overlooked. This is especially true in the UK’s urban parks, gardens and other green spaces, where not much is known about their distribution and diversity.
Compost and other organic fertilisers were associated with the presence of more earthworms. Image © Halfpoint / Shutterstock.
How can I support earthworms in my garden?
To plug this gap, Earthworm Watch brought together thousands of volunteers in one of the largest community science projects of its kind.
For the project, volunteers were asked to compare the number of earthworms living in two 20-centimetre square patches of different habitats. Once they’d selected their sites, they then had to dig 10 centimetres beneath the soil to identify the earthworms living there.
But what about the anecic earthworms, who can live much deeper than this? To count these earthworms, participants poured a mixture of mustard powder and water onto the patches, letting it soak down into the soil.
While this doesn’t harm the earthworms, or the soil, the spiciness of mustard is a mild irritant, causing them to come to the surface. Without it, as many as half of all deep-living earthworms might be missed, making the results less useful.
The resulting data was then sent to the Earthworm Watch team, whose analysis has now been published. They found that the average number of earthworms in the UK’s urban soils is similar to other areas of Europe.
Digging deeper into the findings, the researchers found different earthworms prefer different habitats. Anecic and endogeic worms prefer lawns and meadows, while epigeic species prefer to live in the leaf litter under shrubs and hedges.
This means that worm diversity in urban areas can be supported by providing a range of different habitats. The only habitat all earthworms were less common in were flowerbeds, possibly because these soils are regularly disturbed.
The paper also suggests gardeners can give earthworms a boost by using organic fertilisers like compost and manure. These give the worms something to feed on and can offset the impact of disturbances in areas like vegetable plots.
Though the findings provide an important insight into the lives of urban earthworms in the UK, it’s only one small part of a larger picture. Conducting longer term surveys over a wider area could provide valuable insights into how earthworms are faring in the Anthropocene.
“As part of the National Education Nature Park, I’m working with schools and colleges across England to improve their grounds for nature and wellbeing,” Victoria says. “I’m hoping we can incorporate the monitoring of earthworms and other soil animals as part of that, allowing us to find out how they can be best supported.”
