Climate change has split Europe’s rainfall patterns into two extremes in the form of long droughts punctuated by sudden, intense downpours. These patterns harm crops, wash nutrients from fields, and destabilize farming systems that depend on predictable water cycles. Grasslands, especially the dairy pastures that blanket millions of hectares, lie at the heart of this challenge.

L.terrestris has an important role in this story. Unlike many earthworm species that live near the surface or burrow horizontally, L. terrestris digs deep, sometimes up to two meters, and in extreme cases even deeper. These vertical shafts act like natural drainage pipes. They allow rainwater to infiltrate quickly rather than pooling on the surface, and they create pathways for roots to reach deeper moisture during droughts. In other words, they help buffer both extremes: floods and droughts.

But despite being native to western Europe, L. terrestris isn’t present everywhere it might be useful. Many grasslands have only sparse populations, or none at all. This puzzle prompted research by van de Logt and colleagues, exploring why L. terrestris occurs in some grasslands but not others, and whether reintroduction could restore its ecological services.

In a 2023 study, van de Logt investigated L. terrestris populations across 31 individual grassland pastures, with two sampling points per pasture, on sandy soils in the Netherlands. The goal was simple: to uncover what makes certain soils hospitable, or hostile, to this deep-burrowing species. The results revealed a delicate balance between soil properties, water conditions, and even possible competition from other worms.

The researchers found that texture matters, especially silt content. One of the strongest predictors of L. terrestris abundance was the amount of silt in the soil. Worm populations were far higher in loamy sands, soils with a good mix of sand and silt, than in pure sand. In some fields, densities reached more than 400 individuals per square meter. Silt helps retain moisture, reducing the drought stress that worms face in highly sandy soils. Surprisingly, though, L. terrestris was still found in several very sandy sites, suggesting the species is more flexible than previously believed.

The depth of the gley layer, meaning a layer of waterlogged soil that is an indicator of how high the water table rises seasonally, also played a role. Worms preferred soils where water tables stayed low enough to avoid flooding their burrows. Shallow groundwater, which can create temporary oxygen deprivation, limited their presence.

Another earthworm species, Lumbricus rubellus, seemed to compete with L. terrestris in several sites. Across the study area, higher numbers of L. rubellus correlated with fewer L. terrestris individuals, perhaps because both species consume the same plant litter.

Researchers expected that older grasslands, those undisturbed by ploughing, would support more L. terrestris, since deep burrows can take a lot of time and energy to establish. But surprisingly, grassland age didn’t significantly predict worm abundance in this study. Other factors, such as soil texture and hydrology, appear more decisive.

Together, these findings highlight a complex ecological niche: L. terrestris thrives where soils are neither too coarse nor too wet. But understanding where worms naturally occur is only half the journey. The next question was: Can we help them recolonize landscapes where they’ve disappeared?

Between 2021-2022, van de Logt conducted an ambitious field experiment to test whether L. terrestris can be successfully introduced into pastures, including those where the species had been absent for years.

The experiment was elegant: at two Dutch farms, the team installed 61-cm-wide mesocosms, large steel cylinders sunk into the soil, to create controlled mini-ecosystems. Some were in fields where L. terrestris already lived; others were in fields where it had never been found. Because the researchers inoculated a pasture where L. terrestris already lived, they were sure that the environment was not a limiting factor, and it allowed them to see the effects of the inoculation procedure in itself.

Into each mesocosm, researchers introduced 15 L. Terrestris earthworms from either local Dutch populations, collected on site, or commercially imported Canadian stock, purchased from the bait industry. There were also control mesocosms, into which the researchers did not introduce any worms, and they only contained the indigenous community. This allowed the team to test whether locally adapted worms survive better than imports, and whether the presence of an existing worm community affects colonization success.

A year later, the mesocosms were carefully excavated, all the soil was hand-sorted, and every earthworm was counted, and identified to species level. Encouragingly, in both locations, L. terrestris survived for a full year and produced offspring. This confirms that inoculation, adding worms to restore a missing ecological function, is feasible.

At the site where L. terrestris was already present, local worms tended to survive somewhat better (though the trend wasn’t statistically strong) than Canadian worms. At the worm-free site, the worms survived at similar rates, but the best performance in terms of highest survival and reproduction, was seen in local worms within undisturbed soil. This suggests that local adaptation matters and that using native stock may be the best ecological practice.

In half the mesocosms, researchers removed and hand-sorted the soil to eliminate the existing worm community before inoculating it. Surprisingly, this “clean slate” didn’t boost L. terrestris survival or reproduction. Undisturbed soil often performed just as well or better. This is good news: farmers don’t need to till or disturb their grasslands in order to reintroduce the species.

Taken together, the two studies form a compelling narrative about the future role of L. terrestris in European grasslands. The ecological services provided by L. terrestris, meaning deep burrows, improved infiltration, and drought buffering, directly address some of the most pressing challenges of climate change. Encouraging their presence could reduce reliance on mechanical or engineered water-management systems.

Even sandy pastures can host thriving L. terrestris populations if they contain enough silt and avoid extreme groundwater fluctuations. This opens possibilities across large areas of the Netherlands and beyond. Van de Logt’s mesocosm experiment demonstrated that introducing worms may be feasible, even in places where they’ve been absent for years, but longer-term studies are required to confirm this. Over the long term, released worms could potentially establish permanent populations. Local populations appear better suited to local conditions, reinforcing a general ecological principle that native is best.

The work of Roos van de Logt and her collaborators shows that by understanding and supporting species like L. terrestris, we can harness natural processes to build resilience, restore ecological balance, and prepare our landscapes for an uncertain future.