Millions of large, regularly spaced dirt mounds dot a Brazilian region roughly the size of Great Britain — and all because of termites.
The forests of northeastern Brazil boast some 200 million earthen mounds, each between two and four metres tall, roughly nine metres across and up to 4,000 years old. Oddly, each hill is spaced about 20 metres from any other hill in any direction.
Curious about these knolls, Stephen Martin at the University of Salford in Manchester, UK, and his colleagues examined satellite images of the area, as well as cross-sections of hundreds of the hills. Most were solid dirt. But those built more recently contained a tunnel leading to underground channels excavated by the subterranean termite Syntermes dirus.
The researchers suggest that the mounds are accumulated dirt that termites discarded as they dug their underground highways. The insects dumped the dirt at many evenly spaced locations, minimizing the time taken to reach a disposal site from any part of the network.