Wriggling unseen beneath the surface, earthworms may be responsible for up to 140 million metric tons of global food production each year, a new study estimates. And that’s just looking at their growth-enhancing contributions to a dozen or so crops: their widespread benefits could be generating millions more tons.
Known as ‘ecosystem engineers’, earthworms recycle organic waste into nutrients, improve soil structure, and even boost plants’ immunity to pathogens. It’s common knowledge that these organisms do good things for plants—and in fact there are at least 58 studies looking at specifically what happens to crop biomass when earthworms are added to the soil. It’s universally good news.
But the new Nature Communications study is the first to actually draw together this body of research to quantify earthworm benefits on global scales. Taking those 58 studies, the researchers on the new paper analyzed the worms’ benefits on the many different crops that were represented, from wheat and rice, to maize, barley, and legumes including soybeans, lentils, and peas.
In this mix was also a variety of soil types and levels of fertilizer application, which allowed them to isolate and weigh up earthworms’ benefits against these other factors. Then, taking the findings from this body of research, they combined it with world maps of earthworm abundance, which allowed them to extrapolate the data to a global scale.
Across all studies, the researchers found that the nutritional boost that earthworms provide contributes an impressive 23.3% average increase to the aboveground biomass of crops. When they extrapolated that out to the globe, taking soil types and fertilizer quantities into account, they estimated that earthworms and their tireless underground engineering contribute to 140 million tons of food production each year.
In crop terms, that tonnage equates to 6.5% of global grain yields (128 million metric tonnes), which includes wheat, maize, barley and rice; and 2.3% of all legume crops farmed worldwide. When the researchers split the results by region, they found that in terms of total yield, earthworms had the biggest benefit on crop growth in South Eastern Asia, and Europe, where high earthworm abundance underpinned 40 million metric tons of grain yield in each region, or about 7.4% of the total for each place.
But earthworms’ relative contribution in the global South was higher—accounting for 10% of total grain production in sub-Saharan Africa for instance, and 8% in Latin America and in the Caribbean. This larger share may be due to the comparatively less nutritious soils and lower fertilizer inputs in tropical southern regions, which makes earthworms’ soil-enhancing benefits really stand out, the researchers explained.
That such a huge chunk of global food production rests on the shoulders of such tiny organisms is an exciting finding—which also has some caveats. The researchers note that many of the studies that they relied on involved experiments where worms were artificially added to the soil: that may not always reflect the complex reality of life out in a field, with potential consequences for those impressive biomass estimates. But equally, the simplicity of some of the data, as well as geographical gaps in the research from southern locales, may not accurately reflect the full richness of earthworms’ contribution to the soils and to crops, possibly leading to underestimates.
“I was surprised by the absolute number—128 million metric tons of grain per year is a lot of food!” says the study’s lead author Steven Fonte, associate professor of agroecosystem ecology at Colorado State University. “However, I suspect that our estimate may actually be a bit low, as the global maps of earthworm abundance that we used, in part, to do our calculations may underestimate the abundance and diversity of earthworms in many tropical regions.”
Ultimately, the study proves something that every farmer intuitively knows: the importance of earthworms for our food, but on a scale we didn’t previously appreciate. Yet if the researchers want there to be one takeaway, it’s not that we should start adding earthworms to the soil. Rather, they think we should go back a step further and start by first improving the health of the soils they call home—with methods like no-till farming, and reducing chemical additives—and not just for worms, but the wider community of soil-enriching organisms of which they are part.
“This should go beyond earthworms,” Fonte says, “and consider the full gamut of soil organisms, which is thought to account for more than half of all biodiversity on the planet.”
Fonte et. al. “Earthworms contribute significantly to global food production.” Nature Communications. 2023.
Image: Photo by Ivan Ivanovič on Unsplash
