GROUNDBREAKING research into soil worms has revealed that the world’s largest animal populations are found in high-latitude sub-arctic soils.

The study, by the Crowther Lab, is the first to map the global distribution of soil nematodes, tiny creatures also known as roundworms, which make up an estimated four fifths of all terrestrial animals and play a critical role in soil nutrient cycling, plant growth and the climate.

The study provides conclusive evidence that the majority of the world’s animals live in high latitudes: 38.7% of soil nematodes exist in boreal forests and tundra across North America, Scandinavia and Russia; 24.5% in temperate regions; and only 20.5% in the tropics and sub-tropics.

It also calculated that the world’s population of soil nematodes is far greater than previously estimated, with 57 billion for every single human, with a total biomass of around 300 million tonnes – approximately 80% of the combined weight of Earth’s human population of 7.7 billion people.

Dr Johan Van den Hoogen, lead author of the study, said: “There’s an immense world hidden just beneath our feet that we barely understand. This study fundamentally changes our understanding of the distribution of life on land. We were amazed to find that nematodes are so abundant and that there are more animals in the arctic and sub-arctic than in the tropics – the opposite of what we see above ground.

“Soil organisms are the most important but least understood part of the Earth’s biosphere. Protecting biodiversity and developing effective climate change strategies will require us to model biological activity across the world’s soils and plan how best to manage ecosystems.”

Nematodes play a critical role in the cycling of carbon and nutrients and are essential to understanding biological activity in the soil. They feed on bacteria, fungi, plants and other soil organisms, fulfilling key roles in the food web. They play a significant role in influencing CO2 emissions from soils, determining whether carbon is locked up in soil organisms or released into the soil and the atmosphere. Their activity helps create healthy soils and conditions for plants to grow and capture carbon.

Nematodes are generally more active at higher temperatures, so the large nematode populations in the arctic and sub-arctic make these regions very sensitive to warming. “These regions compose a major reservoir of soil carbon stocks, and may release much more carbon as a result of increased soil animal activity and a prolongation of the plant-growing season due to human-induced climate change,” concluded the research paper.