Earthworm numbers have declined by one third

Researchers estimated the number of earthworms had dropped by 33% to 41% in the last quarter of a century. Photograph: blickwinkel/Alamy

From The Guardian

Populations of earthworms in the UK may have fallen by about a third in the past 25 years, an assessment has shown.

Earthworms are vital for the healthy soil that underpins all ecosystems and scientists said a large decline would sit alongside concerns about “insectaggedon” and the global destruction of wildlife.

Plunging populations of insects have been relatively well recorded. But, despite their importance, there has been no long-term monitoring of soil invertebrates.

To fill the gap, researchers collated data from more than 100 different smaller studies ranging from 1928 to 2018. From this they estimated a decline in earthworm abundance of between 33% and 41% in the last quarter of a century, the period for which the best data was available.

The research is being presented at the British Ecological Society’s annual meeting in Edinburgh on Monday and is being peer-reviewed for publication.

“It’s looking like there is evidence of a long-term decline,” said Prof James Pearce-Higgins, the director of science at the British Trust for Ornithology, which conducted the research. “A large-scale decline in soil biodiversity – particularly the loss of earthworms – would sit alongside concerns about ‘insectaggedon’ and the wider biodiversity crisis.

“It would have widespread impacts on the species that feed on soil invertebrates, like birds, but also affect soil processing and nutrient cycling, the whole functioning of our ecosystems,” he said. “Thrushes, starlings and many waders that rely on soil invertebrates are in long-term decline. These declines are greatest in south-east England where hotter, drier summers may also reduce the availability of earthworms to foraging birds.”

Dr Ailidh Barnes, also at the BTO, said there were good reasons to expect declines in earthworms on farmland. “Changes in the UK countryside over the last century, such as extensive drainage, pesticide use and inorganic fertiliser application, are likely to have negatively affected earthworm populations.” Repeated ploughing was also likely to cause harm.

The scientists scoured thousands of studies to find those containing suitable data. They then took account of differences in the methods used to provide the best window into the past available in the absence of a formal monitoring programme. They found earthworm declines appeared greatest on farmland and in broadleaved woodlands. Wilder upland areas, further from human activity, were less affected.

The team concluded: “The [study] suggests that a previously undetected biodiversity decline has occurred in the UK that could have wide-ranging consequences for ecosystem structure and function.”

Pearce-Higgins said the team hoped the study would prompt further investigations and the establishment of proper monitoring. “We need to be concerned about what is happening to biodiversity below the ground in order to protect the biodiversity that we see above ground. We need to look after earthworms.”