19 January 2023

Missing invertebrates: the UK has already lost a third of its earthworms


The biodiversity crisis is also affecting invertebrates. In the United Kingdom, says a study by the British Trust for Ornithology (BTO), the abundance of earthworms in the soil declined by 33 to 41 percent. Poor agricultural practices are a crucial determinant

by Matteo Cavallito


In the United Kingdom, the population of earthworms, invertebrates essential to soil health, may have declined by more than a third over the past 25 years, a research by the British Trust for Ornithology (BTO) has found. The work has been presented in recent weeks at the annual meeting of the British Ecological Society in Edinburgh.

The study, whose conclusions were quoted by the Guardian, is the result of an analysis of more than a hundred research studies conducted on a small scale over the space of a century. “It’s looking like there is evidence of a long-term decline,” said James Pearce-Higgins, scientific director of the BTO quoted by the British newspaper. “A large-scale decline in soil biodiversity – particularly the loss of earthworms – would sit alongside concerns about ‘insectaggedon’ [insect population collapse, ed.] and the wider biodiversity crisis.”

The decline in earthworms ranges between 33 and 41 percent

By comparing methods used in previous research, scientists were thus able to estimate the change in the earthworm population assuming a decline of between 33 and 41 percent over the past quarter century. The decline of these invertebrates was found to be greater in agricultural lands and broadleaved forests. More isolated upland areas with less human activity were less affected by the phenomenon.

“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,” said the authors, quoted by the Guardian.

According to Ailidh Barnes, a BTO researcher involved in the study, “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 of fields is also among the causes of the decline, she added.

Invertebrates play a crucial role in soil

The consequences of this trend appear very serious. According to Matt Shardlow, executive director of the environmental association Buglife, quoted again by the British newspaper, earthworms are essential to soil health and ecosystem productivity, and their decline is “deeply alarming.” The central role of invertebrates in maintaining soil health, after all, has long been a major topic for researchers.

Indeed, these organisms are known to play a key role in the provision of ecosystem services, participate in the interactions between physical, chemical and biological processes and are ultimately a true indicator of soil quality itself.

In addition, invertebrates are co-responsible for decomposing dead leaves, releasing nutrients and sequestering carbon in the soil. These actions contribute to maintaining fertility and antagonizing climate change.

The biodiversity crisis

The decline in earthworm numbers represents one of many related phenomena contributing to fueling the overall biodiversity crisis in the United Kingdom. In July, the British Environment Agency released a report on the scale of the phenomenon, highlighting its deep historical roots. Industrialization that began earlier than in other nations, the survey noted, helped spur widespread land-use change by depleting natural diversity.

Since the Industrial Revolution, 99.7 percent of marshes, 97 percent of grasslands, 80 percent of lowland heaths, 70 percent of ancient woodlands and 85 percent of salt marshes have disappeared in England alone.

Urbanization, of course, has also played its part. Since 1945, the development of coastal settlements has led to the destruction of 20% of sand dunes, salt marshes and reefs. To date , finally, a quarter of the mammals found in England and nearly a fifth of the plants in the United Kingdom are threatened with extinction.