Africa’s Mysterious 'Fairy Circles' Explained

Found mainly in the grasslands of southern Africa, the oddly shaped formations can grow to more than 65 feet (20 meters) wide, but no one knew what caused them. Now, perhaps dashing the hopes of those who thought actual fairies were involved, a new study has found a possible explanation: termites. (See videos of ants and termites.)

It seems the culprit—or landscape artist if you prefer—is a particular species of sand termite, Psammotermes allocerus, that was found at all of the hundreds of sites studied along a 1,240-mile-long (2,000-kilometer-long) belt of desert from central Angola to northern South Africa.

It works like this: Termites munch away at grass roots, making the soil less dense and more porous and creating a sandy donut hole cleared of plant life. Since plants transpire—or evaporate water into the atmosphere—these vegetation-free sandy centers are able to absorb and retain water more efficiently than if plants were present. (Related pictures: “Nature’s Perfect Circles.”)

The resulting reservoir of water that builds up under the fairy circle allows the surrounding ring of vegetation to flourish in the form of perennial grasses, which in turn provide the termites with food, according to the study, to be published tomorrow in the journal Science.

Termites Farm “Plantations”

By circling the wagons in such a manner, the ecosystem is often able to persist for decades. The question is: how do the termites know to stop eating once they’ve cleared the center? According to study leader Norbert Juergens, of the University of Hamburg, what’s going on is a form of “ecosystem engineering.”

“I believe that the termites stop their grass-destroying activity at the margin of the bare patch based on evolved behavior,” Juergens said by email.

“Thereby, they allow the formation of the perennial grass belt that could be interpreted as a grass ‘plantation.’ Functionally that grass is not touched, but left as an insurance for a series of extreme drought years.” (See a map of Earth’s grassland hot spots.)

These termite farmers also create opportunities for other species, which then establish themselves in the newly created ecosystem.

For instance, the study found that fairy circles attract a variety of organisms, including several species of ants, bees, wasps, plants, and small mammals.

Indeed, by creating these circular oases, the termites turn “wide desert regions of predominantly ephemeral life into landscapes dominated by species-rich perennial grassland, supporting uninterrupted perennial life even during dry seasons and drought years,” according to the study.

Which, you might say, makes the humble termite a fairy godmother of sorts indeed.