Andrew Ross organises regular surveys of earthworms in our soil at Highbridge Community Farm. He explains why we do these surveys and what we learn.
Why we do worm surveys
Having a healthy soil is important if we wish to grow healthy, nutrient rich plants at Highbridge farm and eat healthily ourselves. Worm surveys are one of a few ways we use to monitor the health of our soil. We also have a nutrient analysis conducted every two years or so, which tells us the levels of organic matter (a measure of carbon and nitrogen levels), phosphorus (which is higher than we would wish) and potassium.
The National worm survey
In early February and March 2018, Dr Jackie Stroud, a Natural Environment Research Council Soil Expert at Rothamsted Research, led a project to study the worms in farm soils. A total of 126 farmers took part. We joined the project in 2019 following the national method, and have done a survey annually since, with the exception of last year, when the soil was so dry that there were very few worms in the top 20cm of soil.
How we do the survey
Each team digs a soil pit 20cm x 20cm x 20cm on their plot and removes all the soil to a tray. They then carefully sort through this sample and remove any worms they find into a smaller pot containing a little water (to keep the worm skins moist for breathing). Then we count the total number of worms in the sample and then divide them into adults and juveniles. Adults are identified as those having a saddle on their bodies which juveniles don’t have. The juveniles are counted and then returned to the soil. The adults are then sorted into one of three groups of worms with different roles in the soil ecosystem before being counted. Then all worms are returned to the soil.
The photo below allows you to allocate any worm to one of the three main types (plus compost worms).
Epigeic worms are small or medium sized darkish red worms that live on or very near the surface of fields with abundant leaf litter and feed on the leaf litter and deposit smaller, broken-down bits in the leaf litter for other organism to feed on, so accelerating the breakdown of leaf litter.
Endogeic worms are small or medium pale worms which are grey, pink or green or bluish. They make horizontal burrows through the soil to move around and to feed. In doing so, they mix soil and help release nutrients for plant uptake and so help to raise crop productivity.
Anecic earthworms are the large pencil sized worms which were heavily pigmented red or black . They make permanent vertical burrows in soil. They feed on leaves on the soil surface that they drag into their burrows. They also make middens (piles of casts) around the entrance to their burrows. The are great for making long vertical holes in the soil which improves drainage and allows more oxygen to get to the plant roots.
Our results
The table shows the number of adults counted each year in the soil sample taken from the even numbered plot. The figures list the numbers of first epigeic, then endogeic and then anecic worms.
| Plot | 2019 | 2020 | 2021 | 2023 – to come |
| 2 | 0,3,0 | 3,0,1 | na | |
| 4 | 5,3,1 | 6,2,2 | 1,3,1 | |
| 6 | 0,6,1 | 0,0,0 | 0,0,0 | |
| 8 | 2,5,0 | 1,6,1 | na | |
| 10 | 0,6,1 | 1,0,0 | 1,0,0 | |
| 12 | 0,0,0 | 1,2,0 | 2,2,0 | |
| 14 | 0,4,5 | na | 0,0,0 | |
| 16 | 0,2,0 | 0,6,1 | 0,0,1 | |
| 18 | 1,4,0 | 1,0,0 | na | |
| 20 | 1,1,0 | 0,0,1 | 2,0,2 | |
Average per plot | 14.1 | 7.14 | 7.42 | |
| Average juveniles | 8.6 | 4.14 | 4.33 | |
| Average epigeic | 0.9 | 1.3 | 1.3 | |
| Average endogeic | 3.7 | 1.2 | 0.8 | |
| Average anecic | 0.8 | 0.5 | 0.9 |
Our results suggest that the numbers of adult worms went down from 2019 to 2020 and 2021. There are two possible explanations for these results. Either our farming practices are harming the soil for worms or changing seasonal weather (drier weather) may cause the endogeic and anecic worms to move lower in the soil. Rainfall for the months of January to March in Allbrook is shown below.
| Month | 2019 | 2020 | 2021 | 2022 | 2023 |
| Jan | 29 | 102 | 88 | 25 | 148 |
| Feb | 74 | 162 | 68 | 72 | 5 |
| Mar | 87 | 61 | 18 | 55 | 96 (to Mar 27th) |
This March has been the wettest in 5 years, so we are hoping that our worm numbers will be higher than in the last couple of counts and that worm numbers are more strongly influenced by soil moisture and not by our harmful farming practices!
What the each group of worm results will tell us
Epigeic worms tell us if there is sufficient plant material remaining on or near the surface of the soil for these worms to feed and hide in and thus survive. Intensive cultivation, clearing of crop debris and long periods of bare soil often result in a reduction of these numbers and so less organic matter is made available to soil dwelling organisms and the soil ecosystem begins to break down..
Endogeic worms do a lot of the mixing of the soil and making nutrients available where the roots are growing. These are usually the last group of worms to decline in a soil.
Anecic worms feed on leaf litter at night and pull leaves and organic debris from the surface down into the earth. When the soil is dug their permanent burrows are disrupted and frequent digging often causes a decline in their numbers and a subsequent loss of aeration and drainage channels in the soil. It may be that the teams that practice minimum dig (Teams 1-4) and using green manures (Team 3-4) will have higher numbers of certain types of worms. All this will be revealed by the data we collect.
For further information, see Mariko White. What can worms tell us about our soils? (Hampshire and Isle of wight Wildlife Trust. Published online 31.7.2019).