Termites are the 'fairies' behind weird desert rings

It seems the culprit behind the mysterious "fairy circles" of the Namib desert has been under our noses all along.

The fairy circles are discs of barren sand several metres across, surrounded by lush grasses that stand out against the sparse vegetation. Since the 1960s, theories about their origin have been raised and quickly shot down. A study in 2004 seemed to rule out the three leading theories: radioactive soil, toxic debris left by plants, and termites.

But perhaps the researchers didn't look hard enough. When Norbert J?rgens of the University of Hamburg in Germany examined hundreds of fairy circles in over 2000 kilometres of the Namib desert in southern Africa, he found a species of sand termite, Psammotermes allocerus, was the only organism consistently present.

J?rgen observed the insects eating grass roots, killing plants before they could sprout through the soil. With no foliage for water to transpire from, the water is retained in the ground beneath the patches, helping the termites survive the dry conditions. Their burrows make the soil more porous, allowing rainwater to percolate down to the cooler, deeper sand, again reducing the amount of water lost from the surface.

The extra water in the soil means that grasses spring up at the boundary of the insects' circular foraging area, attracting other life. "They are turning desert into grassland inhabited by numerous plant and animal species," says J?rgens.

"This is an amazing phenomenon" but unsurprising, says Nathan Lo from the University of Sydney. In arid regions of northern Australia, termites build mounds that trap nutrients, and an ecosystem develops around them. The circles are "like flattened termite mounds", he says.

But not everyone is convinced. Walter Tschinkel, a biologist from Florida State University in Tallahassee who has previously published work on fairy circles, suspects J?rgens is confusing correlation with causation. "It is more plausible that the grass died of other causes and was then consumed by termites," he says.

Lo disagrees, pointing to photographs J?rgens took showing the termites nesting in the roots of plants that are still alive. "This is about as good as you can get," he says. "It's very strong evidence."

J?rgens says he cannot exclude the possibility that "there could still be an unknown invisible bacterium, fungus or fairy", but so far none has shown itself.

Journal reference: Science, DOI: 10.1126/science.1222999

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