New research will unveil the impact of climate change on soil earthworms

A University of York study will assess how climate change-induced flooding affects the survival of earthworms, creatures essential for maintaining soil health

by Matteo Cavallito

Earthworms play an essential role in keeping soil healthy by eating and recycling organic matter. But their future is under threat due to the increasing intensity, frequency and extent of flooding. Therefore, British researchers now argue, it is essential to analyse these phenomena and their impact on invertebrates in the context of climate change.

Embarking on the mission is a group of scholars led by Professor Mark Hodson, a researcher at the University of York, as part of a project announced on the eve of the recent World Earthworm Day. The two-year analysis will engage the authors in field sampling, laboratory experiments and modelling. In addition to examining the effect of extreme weather phenomena, the research will also look at how changes in the habitats of these specimens are affecting the soil.

Climate change favours floods

Climate change impacts the water cycle by, among other things, favouring phenomena such as flooding, which obviously complicates the existence of invertebrates. Unlike humans, the scientists remind us, earthworms – engaged in creating networks of tunnels that promote drainage and aeration – have no lungs and breathe through their skin.

They can therefore survive in water as long as it contains sufficient oxygen. The problem, however, is that once flooded, soils can become oxygen-deficient. Thus causing the earthworms to drown.

The study aims first of all to measure the creatures’ sensitivity to soil moisture levels, thus assessing how wet the soil must be before they start moving in search of drier areas. At the same time, it reveals whether or not reduced oxygen concentrations damage the cocoons left by the earthworms themselves and reduce their likelihood of hatching.

Water tolerance varies between invertebrate species

Previous investigations conducted by the University of York itself have found that the oxygen concentrations at which earthworms drown vary between species without any known reason. One hypothesis put forward by the scientists is that different varieties of invertebrates exhibit differences in haemoglobin and the ability to estivate. That means the ability to go into a prolonged period of dormancy and reduce their metabolic rate and thus their demand for oxygen.

The researchers, however, emphasise how different earthworm species affect soil properties and functions differently.

Therefore, changes that occur in their earthworm communities, due to variable survival in flooded soils, could in turn have an impact on the soil. Invertebrates, the authors add, can stimulate plant growth by up to 30%, thus contributing to global food security. According to some estimates, for example, these creatures are responsible for 6.5% of the world’s grain production.

Earthworms are in danger

The issue is particularly relevant, especially in the UK. In the country, in fact, the population of earthworms may have declined by more than a third in the last 25 years. This was suggested by research by the British Trust for Ornithology (BTO), presented at the Ecological Society’s annual meeting in Edinburgh in late 2022. The study, whose conclusions were taken up 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.

By comparing methods used in previous research, the scientists were able to estimate the change in the earthworm population. They assumed a decline of between 33 and 41 per cent over the last quarter century. The decline of these invertebrates was greatest in agricultural land and deciduous forests. More isolated mountain areas, characterised by less human activity, have been less affected by the phenomenon.