In 2019, a remarkable initiative involving 15,000 primary school children across the UK took place, not on sports fields but in local green spaces where they engaged in digging up worms and spotting and counting birds.
“The kids were just so enthusiastic about it. It was incredible,” said Blaise Martay, lead researcher from the British Trust for Ornithology (BTO).
Martay was initially concerned about the reliability of the data, given the varying enthusiasm levels of children. However, the results “showed exactly what we’d expect”, she said, demonstrating a correlation between the abundance of earthworms and higher populations of blackbirds, robins, and thrushes—species that depend heavily on earthworms for their diet.
Earthworms are crucial yet often overlooked players in the ecosystem. They break down organic matter, enriching the soil which is vital for other organisms. Their activities help create tunnels that facilitate the passage of air and water, which enhances soil health and biodiversity—elements critical for agriculture as 95% of the planet’s food is grown in topsoil.
Charles Darwin, fascinated by earthworms, dedicated his last book to them, emphasising their significant but understated impact on the world’s ecological and historical landscape. He told his son William that what he hoped his book would reveal was that “worms have much bigger souls than anyone would suppose”. Darwin thought that “it may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures”, and his book was a bestseller.
Despite their importance, a 2023 national assessment revealed a troubling decline in UK earthworm populations, which have decreased by a third over the past 25 years. This decline is likely to have profound impacts on soil health, ecosystem structure, and function, according to a 2024 horizon scan by Trends in Ecology and Evolution.
“Such declines would likely have significant effects on soil health, ecosystem structure and function,” researchers wrote.
Dr. Ailidh Barnes from BTO, who led the assessment, notes a consistent decline in earthworm populations by up to 2% annually.
“We know birds that feed on earthworms are declining so we were wondering what was happening with the worms,” said Dr Ailidh Barnes, a research ecologist from BTO who conducted the national assessment.
The most notable reductions were observed in broadleaf woodland ecosystems, potentially exacerbated by climate change-induced soil dryness or agricultural runoff.
“That was the finding we were most surprised by,” said Barnes.
This loss might be influencing broader woodland ecology more than previously understood, coinciding with a 37% reduction in woodland bird populations in British woods since 1970.
Earthworms are indispensable to their ecosystems, acting as engineers that facilitate numerous processes essential for nutrient cycling and soil fertility. Their decline could significantly impact global food production capabilities.
“The loss of worms could be playing a bigger part than we realise,” said Barnes. “Earthworms are vital at looking after the soil, which is the basis of all life and what grows our food.”
A 2023 study likened earthworms’ contribution to the global grain harvest to that of a major country like Russia, producing approximately 140 million tonnes of food annually.
Further research highlights that over half of the world’s species inhabit the soil, yet soil invertebrates remain significantly neglected in biodiversity assessments. The challenges they face include habitat drainage, pesticide use, and inorganic fertilisers, which are prevalent across small study areas but suggest a broader global issue.
Barnes said: “They are vital for everything. When you start talking to people about earthworms they are interested, but they’re under the ground so they get forgotten about.”
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