“WALLY, show her the termites!” Victoria Tschinkel led me to where her husband was kneeling in a circle of sand marked with a bright pink ring. The bare patch in an otherwise grassy desert was one of several that had doused with potent pesticide a few days before. “If termites play a role in killing the grass, then poisoning them should allow the vegetation to grow back,” he says.
He began scooping up handfuls of hot orange sand from around the roots of a dry clump of grass. Each scoop was followed by a silent pause as we scanned the dirt for near-invisible insects. When Tschinkel spotted movement, he dived like a hawk, aspirator to his lips, and sucked the termite up a plastic tube into a little glass vial. He would later examine his captives under UV light, looking for a telltale glow that indicated the insects had eaten the slow-acting poison.
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(Image: Lee Frost/Robert Harding)
The grassy Namibian desert is pock-marked with millions of circular patches of bare earth just like this one. Viewed from above, they make the ground look like a moonscape. Commonly known as fairy circles, the patches range from 2 to 12 metres across and appear in a 2000 kilometre strip that stretches from Angola to South Africa (see map). But nobody knows what they are.
Explanations for what causes Namibia’s fairy circles come and go, like the circles themselves, which grow and fade over time. But so far, none has stuck. Tschinkel was here to change that. He had a hypothesis to test, one he hopes will bring the matter to a close – and there’s no room for termites.
“Explanations come and go, like the circles themselves, which grow and fade”
Few people visit Namibia, a remote country on the west coast of southern Africa. Those who do tend to return with tales of vast sand seas, century-old shipwrecks and ghost towns swallowed by dunes. But it is the fairy circles that have proved most captivating. Local legend has it that they are the footsteps of the gods, or burn marks from the breath of subterranean dragons. These days, you are more likely to be told that they are landing spots for UFOs or places where Bushmen urinate. A few think they are simply the sleeping spots of ostriches or oryx.
Generations of scientists have had different ideas, from radioactive soil to pathogenic fungi. Some claim that they are caused by noxious gases seeping up through the earth, others that they are places where euphorbia bushes grew. These highly toxic plants are said to have once killed a group of 16 travellers who used euphorbia’s deadly wood in their campfire.
Touched by fairy dust
Like most researchers who fall under their spell, Walter Tschinkel, an entomologist at Florida State University in Tallahassee, first encountered fairy circles as a tourist. In 2005, he and his wife visited the NamibRand Nature Reserve, a fairy circle hotspot. One of the staff asked if he could figure out what caused them.
Tschinkel, who studies ant colonies, didn’t think twice. It was obviously termites. “Everyone had thought termites at one time or another,” he says. So the couple returned in 2007, convinced they would close the case within a week. After three days of digging in the circles without a termite nest in sight, Tschinkel realised that his initial hypothesis needed a rethink.
Since that first attempt, Tschinkel, like several others before him, has returned to Namibia repeatedly, moonlighting from his day job to try and crack the riddle. Each field trip yields more questions than answers. In 2009, he seeded some circles with nutrients. He transferred soil from outside the circles to the inside, and vice versa. And he dug several up, laid down a rubber barrier and then refilled them. But none of his experiments made a difference. The fairy circles remained barren and the areas around them continued to grow.
The lack of positive results merely spurred Tschinkel on. Using satellite images and field observations, he showed that fairy circles are “alive” – that is, they come and go from the landscape, with lifespans averaging 41 years. Then he teamed up with two other researchers drawn to the mystery: Michael Cramer, a biologist at the University of Cape Town in South Africa, and Nichole Barger, an ecosystem ecologist at the University of Colorado, Boulder.
(Image: Rachel Nuwer)
In 2013, the pair had built a computer model that revealed rainfall was the most important predictor of fairy circles. The highest densities of circles occurred in sandy, nutrient-poor soils that receive only 50 to 100 millimetres of rain per year. Based on this, Cramer, Barger and Tschinkel began to suspect that fairy circles were the result of fierce competition between grasses living in a stressful environment. This would explain why some studies suggest that circles tend to form after dry years and disappear after wet ones.
As plants jostle for water and nutrients, weaker ones die, providing more resources for their stronger neighbours. This leads to bare patches appearing in between areas of vigorous growth. With no grasses on them to suck up the water, the bare patches can hold underground reservoirs of moisture and nutrients that sustain the stronger, greedier plants that line their edges. These reservoirs have been found to stick around for 8 to 11 months after the last rainfall.
However, without plants growing in it, the surface layer of sand covering the barren spots becomes particularly dry – like a lid on a bucket of water (see “Underground reservoirs” diagram). This could explain why, despite the underground reservoir, new seedlings can’t take root inside the circle. Over time, the system reaches a stable state – in this case, a circular structure – that minimises competition. Similar patterning is seen elsewhere, including tiger-like stripes in Niger, spots in Chad and bands in Sudan. All occur where extremely dry deserts meet wetter grass or shrub lands.
It was a neat solution. But it would take more than fancy computer models to convince the die-hard fairy circle aficionados, many of whom were unwilling to give up on their own hunches.
So in February, Tschinkel, Cramer and Barger met up in Namibia’s capital Windhoek and made the six-hour drive south-west to NamibRand. Holing up in an airy former farmhouse with enough food and wine to sustain them for two weeks, they embarked on a rigorous schedule, heading out shortly after dawn each day and not returning till dusk. I joined the team on their last day of fieldwork, meeting them on a dirt road that branched off into an even smaller dirt road that led to the research enclosure – a tiny patch of ground in the epic orange and sage-green landscape.
“The team holed up in a farmhouse with food and wine for two weeks”
With the help of NamibRand staff, the team had fenced off an area containing 25 fairy circles to prevent equipment-trashing oryx from getting in – a lesson learned the hard way. The plan was to revisit some of Tschinkel’s earlier tests, but ramp up the rigour. Marking the circles with colour-coded rocks, they began a classic plant ecology experiment: some circles would get a full quota of plant nutrients, some would get a steady water supply, some would get both and some nothing at all. If those resources were constraining plant growth, then the circles getting boosters should begin to fill in. They were no longer hoping for a quick answer. “We are adding water at agriculture irrigation rates,” says Cramer.
The team also injected nitrogen-labelled isotopes into the centres of some circles to trace the flow of water. Then they put vertical underground barriers around others to see if stopping water and nutrients from leaving the circle might affect surrounding grasses. Finally, a few circles were dosed with poison to deal with the termite question.
Termite trouble
Tschinkel had long assumed that the termite theory had been laid to rest. But around the time Cramer and Barger were building their computer model, , an ecologist at the University of Hamburg, Germany, published results in the journal Science suggesting termites were indeed to blame. Based on evidence gathered over the course of 40 field trips, JĂĽrgens was convinced that sand termites purposefully engineer the circles to create water troughs. No one had ever noticed them before, JĂĽrgens said, because their fine tunnels are so hard to spot.
One idea is that termites are to blame for fairy circles (Image: Rachel Numer)
There was uproar as termites split the fairy circle fan club once again. The main criticism levelled at Jürgens was that the presence of termites didn’t prove they caused the circles; they may just move in to the basements of existing structures.
The debate had raged in journals and on internet forums long enough. Spotting an opportunity for the different sides to meet, Nils Odendaal, CEO of NamibRand, organised the first ever Fairy Circle Symposium to coincide with Tschinkel, Barger and Cramer’s visit. On a warm February morning, 35 people gathered in a garage-turned-conference room. Even as the first talks began, however, brows furrowed, lips tightened and toes tapped.
Carl Albrecht, head of research at the Cancer Association of South Africa, presented a third hypothesis – one that has earned him the nickname “the gas man”. He thinks that the grass in fairy circles is killed by noxious gases, possibly seeping up from deep underground. He has analysed the roots of dead plants collected from fairy circles and isolated four molecules his team has been unable to identify. Another group at the University of Pretoria are pursuing the same hypothesis and have identified their own set of compounds unique to fairy circles. Albrecht admits this raises more questions than it solves, however. “It’s not clear if those molecules are the cause or the result of something,” he says.
But as the day wore on, the competing plants hypothesis favoured by Tschinkel, Barger and Cramer gained momentum. , an ecologist at the Helmholtz Center for Environmental Research in Leipzig, Germany, showed how aerial images reveal that, over dozens of square kilometres, fairy circles appear in a surprisingly regular hexagonal pattern, almost like a honeycomb. “Only self-organisation is known to cause patterns like this at such a large scale,” he says. “No matter what is found in the field, all hypotheses on fairy circles need to account for both their small- and large-scale patterns.”
Legend says the fairy circles of Namibia were created by dragons (Image: Robert Harding/Plainpicture)
Gas belches from below can kill plants, Getzin says, but the patterns formed are always irregular when viewed over a large area. He also says the same is true for patterns formed by social insects in arid environments.
Jürgens was outnumbered: “I am the only one here supporting the leading hypothesis for fairy circle formation.” He hadn’t planned to speak, but after checking on his car full of termite nests – collected from nearby circles and stashed for later study – he gave an impromptu talk. He outlined his view of how fairy circles are established by termite queens and thereafter always contain the insects, which kill the grass by eating its roots and secreting toxic gas.
Jürgens and his graduate student Felicitas Gunter also have new phylogenetic data showing that sand termites are actually composed of six distinct species, not one, which would explain why they have been found in places where there are no fairy circles. Jürgens thinks some of those species make different types of fairy circle and those living east of the Namib desert don’t make circles at all. He has also done calculations based on aerial images and on-the-ground monitoring that suggest fairy circles have a much longer lifespan – possibly by hundreds or thousands of years – than Tschinkel first estimated.
In the fairy circle whodunnit, are we any closer to the big reveal? Getzin agrees with Tschinkel that the competing plant hypothesis is the one to back. “I think we just need a little time for the idea to settle,” he says. That, and for the results of Tschinkel, Barger and Cramer’s fieldwork to come in – which could take months or years. In the end, it may be that elements of competing theories tell different parts of the same story. Termites might play a role in maintaining existing circles, for example. “It will take more time to put all the pieces together,” says Barger. “This is the great thing about having multiple disciplines involved – trying to assemble the puzzle with just one doesn’t always work.”
Back in the enclosure the Namibian sun was already intense by 8 am. The team had learned not to kneel in the hot sand in shorts – they all had matching knee burns. But if they are to get the answers they hope for, hundreds of dollars’ worth of kit has to function properly in the heat for months, and last minute adjustments could prove crucial. Cramer folded out a portable chair and began tinkering.
This article appeared in print under the headline “In the footsteps of gods”
Article amended on 12 June 2015
When this article was first published it muddled its rainfall measurement. This has now been corrected.
