FORT COLLINS, Colo. – Earthworms contribute significantly to global food production, new research finds.

Researchers estimate that at least 30,000 species of earthworms exist on the planet. The invertebrate animals (yes, earthworms are a part of the animal kingdom) are crucial for soil health. Despite the global significance of earthworms to our planet’s soil, little is understood about how they and other macro- and microbiota present in soil impact agriculture.

“There’s been some recent studies suggesting that soils may contain over half of all the biodiversity on the planet,” said Steven Fonte, associate professor in the Department of Soil and Crop Sciences at Colorado State University. “There’s been very few efforts to try to quantify and really understand what the value is of that soil biodiversity. It’s highly dependent on us humans in a way, and I think we take it for granted.”

Fonte and his collaborators found that earthworms contribute to roughly 6.5 percent of global grain (maize, rice, wheat and barley) production and 2.3 percent of legume production, about 140 million metric tons annually – nearly equivalent to the yearly grain production of Russia. Earthworms likely have a lesser effect on legume production because legumes can fix their own nitrogen.

Worms contribute about 5 percent to Northern America grain production. Worm contributions to grain production were highest in the global south, with earthworms contributing 10 percent to total grain production in Sub-Saharan Africa and 8 percent in Latin America and the Caribbean. In Europe and Eastern/Southeastern Asia, 7.4 percent of cereal grain production was attributable to earthworm activity. Fonte explained that stronger effects were observed in certain areas due to differing soil conditions. In the global south, soils are more acidic and have higher clay content, factors shown to enhance the benefits of earthworms for crops. Additionally, some regions have a higher earthworm abundance than others.

Earthworms contribute to agricultural yield for many reasons. They feed on old crop residue and decaying organic matter, quickly decomposing those materials. Their feces, called casts, are rich in nitrogen and phosphorous and highly available for plants to uptake.

While earthworms have a lot of effects on nutrient availability and soil fertility, they also aerate soils, improve conditions for root growth, and enhance water filtration and capture, Fonte said.

“There are some other things (about the effects of earthworms) that we just really don’t understand well at all. There’s a really cool study I came across about earthworms releasing a hormone in their cast that can stimulate plant defenses against plant parasitic nematodes,” he added. “There’s probably lots of other ways that earthworms are triggering plant responses that have nothing to do with nutrients or water dynamics.”

Fonte believes the effects of earthworms on agriculture could be underestimated, especially because the number of earthworms on the planet is likely underestimated. In 2019, researchers released a global map of earthworm populations. The dataset included observations from more than 6,900 sites across 57 countries. Fonte contributed to the dataset, literally digging up worms at his study sites and counting how many worms were present in the soil he excavated. However, he has also informally surveyed earthworms around the world and said that in some regions, the global earthworm map reported no observations even though he had encountered earthworms there.

While it might be a nearly impossible task to quantify how many earthworms live beneath our feet in soil across the globe, it’s important to understand how they are influencing global food production.

“I think there’s a lot of potential to develop more effective soil management practices that take all of these considerations (about how earthworms influence agriculture) into account,” Fonte said.

While researchers are not encouraging farmers and producers to add earthworms to their soil, there are ways to support already established populations. For example, no-till farming creates a stable environment for worms to survive and thrive. Adding organic materials, like manure or leaving crop residue, can also be beneficial.

Moving forward, Fonte and his team are interested in investigating how global management practices impact not just earthworms but other macrofauna like ants, beetles, spiders, and centipedes that have important functions in soil. A student in Fonte’s lab is interested in understanding how mycorrhizae, or associations between roots and fungi, contribute to agricultural production.

“We should really be paying a lot more attention to all soil biology and the benefits that it’s providing us in our agricultural systems,” Fonte said.