A big thank you to the 1,850 people who took part in Earthworm Watch! Victoria Burton, postgraduate researcher and lead scientist has been busy analysing the results of two years of data collection. Read on to hear what you have helped us find out about earthworms in urban areas.
What types of soil do earthworms prefer?
We found double as many earthworms in clay and loam soils compared to sandy soils. Sandy soils are less suitable for earthworms as they tend to have less organic material (for food) and poor water retention. Indeed we found the smallest number of earthworms in dry soils, with 50% more found in moist soils. Wet soils were somewhere in between, although earthworms need moist soils to survive, too much water reduces the oxygen available for them to ‘breathe’ (although some special earthworms prefer wet soils). We also found 20% more earthworms in sites which used organic compost (such as manure or leaf mould) but there was no change in earthworm numbers when inorganic compost was used.
Which habitats have the most earthworms?
Generally earthworms were not as picky about their habitat as they were about soil type, with most habitats having similar numbers of earthworms. Lawns and meadows had the highest numbers, possibly due to lack of disturbance from digging. Vegetable beds and areas with trees and shrubs also had high numbers of earthworms, probably due to having lots of food in the form of leaf litter or added compost present. The only habitat earthworms did not do well in was flower beds, these had 30% fewer earthworms than other habitats. Perhaps this is due to flower beds being both disturbed by digging and having old plant materials tidied away?
Do different types of earthworms prefer different habitats?
Yes they do! We found the highest numbers of deep-living and soil-feeding earthworms in lawns, meadows and vegetable beds. However, surface-feeding earthworms preferred shrubs and hedges - this type of earthworm feeds on dead leaves rather than soil, maybe there is more to eat in this habitat. Despite this, we did not find high numbers of surface-feeding earthworms in woodlands, so there may be other factors that we did not measure.
How does soil carbon influence earthworm numbers?
It is unclear. The data suggests there are more earthworms in soils with higher carbon content but the relationship does not quite meet the standard scientists use to decide if a result is statistically significant. This is common in scientific research - more data are needed!
What else did you find?
The average number of earthworms per soil pit was eight, which equates to around 200 earthworms per square metre! The time of year and location the survey was completed also affected the results, but only slightly, with the most earthworms found in central England.
How can I help earthworms in my garden or allotment?
We found different earthworm types have different habitat preferences so creating a mixture of habitats in your garden, or leaving wilder spaces in your allotment should increase the diversity of earthworms.Try building a log pile or making a compost heap using Anthony's wildlife gardening tips. If you use fertiliser, stick to organic ones such as well-rotted manure, compost or leaf-mould to increase earthworm numbers. If you have a dry or sandy soil adding organic fertiliser will also help with water retention and make the soil more hospitable to earthworms. For further information about composting, visit the Garden Organic website here and the RHS have a great article on making compost. Some useful information about earthworms and ways to help is also available in the Wild About Garden’s Go Wild for Worms guide.
If you would like to learn more about earthworms and soil health, visit the Earthworm Society of Britain, or you could join one of the Learn to Love Earthworms courses. Don’t forget to see what other research projects you can take part in with the Natural History Museum and Earthwatch Institute.
Thanks again from the Earthworm Watch team!