By building “fairy circles,” termites engineer their own ecosystem | Ars Technica

The Namib Desert is dotted with thousands of mysterious “fairy circles,” which are near-perfect circles of barren soil two to fifteen meters wide, rimmed by tall grass. They are unmistakable and stretch for miles, giving the landscape an ethereal and otherworldly feel. Many possible explanations have been proposed, including toxic substances in the soil, meteorites, termites, UFOs, and the ghosts of dead natives. But the circles are extremely remote—more than 110 miles from the nearest village—and have been difficult to study scientifically. Despite decades of research, the cause of these bizarre circles has remained elusive.

But now, after a six-year study and more than 40 trips to the Namib Desert, Dr. Norbert Juergens believes he has come to understand the biological underpinnings of this strange phenomenon. According to Juergens, a single species of termites is responsible for creating and maintaining the circles. But the barren circles aren't just a byproduct of these tiny insects living below the sandy desert surface; they are part of a carefully cultivated landscape that helps the termites—and many other organisms—thrive in an otherwise inhospitable climate.

Juergens hypothesized that if the fairy circles’ cause was biological, the organism would need to co-occur with the circles and would probably not be found elsewhere. Only one species fit the bill: Psammotermes allocerus, the sand termite. Not only was the sand termite the only insect species that lived across the entire range of the fairy circles, but these termites were found to be living beneath nearly every circle sampled. And the harder the termites worked – foraging, burrowing, and dumping their refuse – the more grass died, leading Juergens to conclude that the termites keep the circles barren by burrowing underground and foraging on the roots of germinating grasses.

But the story doesn’t end there. The particular structure of the fairy circles—bare soil edged by tall grass— isn't just a side effect of the insects’ hard work. Instead, this characteristic architecture is vital to the termites' success, and even plays a role in structuring the rest of the ecosystem.

Juergens found that the water content of the soil inside the circles was surprisingly high, even at the driest times of the year. Soil humidity between the circles, meanwhile, was much lower. It turns out that the barren ground within the circles allows water to percolate down through the sandy soil and accumulate underground, rather than being taken up by plants and lost via transpiration. The termites living below the circles benefit from this store of water in an otherwise parched desert that receives less than 4 inches of rain annually. Furthermore, perennial grasses also flourish around the circles, thanks to the underground water. The termites then feed on this surrounding grass, expanding their circles ever so slowly.

In essence, the termites are cultivating their own constant sources of water and food by creating and maintaining these circles. It’s a complicated phenomenon, and, more than likely, there’s no actual consciousness or planning involved on the part of the termites; they are just instinctually performing tasks that have been etched into their DNA over millions of years. However, the end result of the insects' behavior is a massive change in their habitat, a process that scientists call “ecosystem engineering.” Just like beavers, sand termites are altering the entire landscape for their own benefit. And, indirectly, they are also helping other species, since fairy circles have been found to increase biodiversity: a disproportionately large number of insects, reptiles, plants, and small mammals are found in and around the circles.

Earlier studies had investigated whether termites were responsible for the circles, but these scientists were looking for a species called harvester termites, and concluded that they played no role. Sand termites are secretive, don't have obvious nests or burrows, and may have eluded these researchers.

But despite this new information, there’s still a lot to learn about fairy circles: for instance, why plants don't grow very well in soil taken from the center of the circles, and what role other species may play in the creation and maintenance of the circles. But for now, we can put the UFO and ghost theories to rest, and acknowledge the humble sand termite for this incredible feat of ecosystem engineering.

Science, 2013. DOI: 10.1126/science.1222999 (About DOIs).