A national on-farm survey found that key earthworm types were rare or absent in 42 per cent of English fields. Counting earthworms is the cheapest soil test in the country: any farmer can do it with a spade in an hour. What the worms are telling us lines up exactly with what the rivers are telling us.
Earthworms are sensitive and responsive to soil management, which is what makes them an ideal indicator of soil health.
A soil health pilot study in England, published in PLOS One, had farmers survey their own fields. It found that key earthworm types were rare or absent in two out of five fields, with 42 per cent of fields showing the absence or rarity of the surface dwelling and deep burrowing groups that indicate a soil is being over-worked.1
The longer trend is worse. A collation of a century of soil invertebrate abundance data suggests long-term declines in earthworm abundance of 1.6 to 2.1 per cent a year, equivalent to a fall of 33 to 41 per cent over twenty-five years, with the steepest declines in broadleaved woodland and farmland.2
It is easy to file earthworms under charming rather than important. They are not charming, they are infrastructure.
Deep burrowing earthworms create vertical channels that carry water from the surface down through the profile. Those channels are a large part of how a field absorbs heavy rain rather than shedding it. Surface dwelling worms process crop residue into the organic matter that binds soil into crumbs. Remove them and you remove both the plumbing and the glue.
The Environment Agency notes that just a gram of soil can contain as many as a billion bacteria, and a hectare can hold roughly 5 tonnes of soil organisms, the equivalent weight of about 100 sheep.3 Earthworms are simply the part of that system you can see with a spade.
This is why the earthworm data and the river data agree. A field with no deep burrowing worms has poor infiltration. Poor infiltration means run-off. Run-off means sediment, and sediment carries phosphate. The 42 per cent figure and the 55 per cent of rivers failing the phosphorus standard are two readings of the same problem.4
The losses below ground are matched above it.
Birds that feed on soil invertebrates cannot live where the invertebrates have gone. This is not a coincidence of separate declines. It is one food chain, and it starts in the ground.
The reason to lead with earthworms is that unlike almost everything else on this site, it costs nothing to measure and no one has to wait for a government scheme to do it.
Dig a spade’s depth of soil, roughly 20 centimetres cubed, hand sort it, and count. Do it in ten spots across a field. The English pilot study was carried out by farmers themselves, and 57 per cent of those who took part said they would change their soil management as a result.1
It will not tell you everything. It will tell you, honestly and immediately, whether the biological part of your soil is still working, and that is more than the national monitoring system currently provides.3
The Soil First Initiative works on the soil itself, using natural soil biology to build structure and organic matter so farmland holds rain and nutrients instead of shedding them. It is done field by field and catchment by catchment, the land stays in full production throughout, and the change is measured in the soil and in the water. See how it works, or read the full evidence file.
The Environment Agency’s own words, and a 2030 target with nothing measuring it.
Thirty-eight per cent of surveyed sites in south west England shed water they should be holding.
A law in 1991. An advice service in 2006. Statutory farming rules in 2018. In 2026, fourteen per cent.