In the seasonally dry, deciduous forests of northeastern Brazil, obscured by walls of thorny-scrubs, is a vast landscape made up of tens of millions of densely packed earthen mounds. These cone-shaped piles of dirt, each measuring thirty feet wide at its base and twice as tall as a grown man, are waste earth excavated by the termites when they burrow tunnels under the soil. Researchers estimate that there are some 200 million mounds here, covering a vast region nearly equal to the size of Great Britain. The amount of soil excavated is over 10 cubic kilometers, equivalent to the volume of 4,000 great pyramids of Giza. This makes them the biggest engineering project by any animal besides humans. Incredibly, some of these mounds are as old as the Pyramids themselves.

The mounds remains largely hidden from view in the deciduous, semiarid, thorny-scrub caatinga forests unique to this part of Brazil. Locals call them murundus but very few people outside of the region have heard about it. It was only in recent decades when some of the lands were cleared for pasture that outsiders have come to discover them.

Roy Funch, from the State University of Feira de Santana, first saw these fields of mounds in the 1980s when he arrived in Brazil as a Peace Corps volunteer. He originally wrote about them in local popular-science magazines, but never managed to stoke much interest in them. Three decades later, after spotting them again on Google Earth, Funch returned to Brazil, this time as a researcher, to learn more about these mysterious mounds.

Funch and his colleagues found that this colossal feat of engineering is the work of a tiny species of termite called Syntermes dirus, barely half an inch long. These creatures have been building this landscape for the past 4,000 years, and they are still present in the soil surrounding the mounds. The youngest mound is about 690 years old, while the oldest was at least 3,820 years old.

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Because these mounds are not nests but discarded earth, they have no internal structures save for a single large central tunnel descending into the ground to meet an extensive network of underground tunnels and narrow horizontal galleries where the termites store harvested food. At night, the termite workers and soldiers emerge from their underground nest and onto the forest floor through small temporary tunnels excavated between the mounds. After their work is done, they return back to the nests and seal the tunnels shut.

The details of the study is published in a recent paper in Current Biology.