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Stephen J. Martin noticed large mounds about 10 feet high by 30 feet wide along the edge of the road as he was crossing a remote area of northeastern Brazil.
"After 20 minutes, we were still riding in these places and I started saying," What are they? " "Said Martin, an entomologist at the University of Salford in England, who was in Brazil for research on the worldwide decline of honeybees. .
He thought that it could be stacks of land displaced by the construction of the road. Instead, his companions told him, "Oh, these are just termites."
Martin recalled his incredulous response: "And I went," Are you really sure of that? "And they are like," Well, I do not know. I think so. & # 39; & # 39;
On a subsequent visit, Martin met with Roy R. Funch, an ecologist at the Brazilian State University of Feira de Santana, who was already arranging radioactive dating to determine the age of the mounds.
I said: Look, there must be thousands of these mounds. And he went, "Nah, there are millions." & # 39;
But Funch had underestimated.
In a research published in the journal Current Biology, Martin, Funch and their colleagues report the results of several years of surveys.
How many mounds? About 200 million, say the scientists.
The cone-shaped mounds are the work of Syntermes dirus, one of the largest species of termites: they are about half an inch long. The mounds, averaging about 60 feet apart, are spread over an area as large as Great Britain.
"As humans, we've never built a city that big, anywhere," Martin said.
The scientists were also surprised when they received the results of the radioactive dating of 11 mounds. The youngest was about 690 years old. The oldest was at least 3,820 years old, or almost the great pyramids of Giza in Egypt. "That's what got me out of the water," Funch said.
Scientists have also estimated that, to build 200 million mounds, termites have excavated 2.4 cubic km of earth, a volume equivalent to about 4,000 large pyramids of Giza. "This is the largest known example of ecosystem engineering by a single species of insect," the scientists wrote.
Another surprise was that the mounds turned out to be just mounds.
Other termites build mounds with intricate networks of tunnels providing ventilation to underground nests.
But, cutting through some mounds, Funch and Martin found only one central tube leading to the summit, without ever finding any nests.
These mounds were not ventilation structures, but simply piles of earth. As termites dug tunnels under the landscape, they needed a place to get rid of the excavated earth. So they carried the dirt in the central tube up to the top of a mound and threw it away.
Young active mounds reach 4 to 5 feet tall in a few years, said Funch. Most older mounds appear inactive. Scientists do not know if this means that termites are gone or they simply do not need to dig further into the area after building the necessary tunnels.
Although people in the area have heard of termites, few foreigners knew it. The extent of termite construction was hidden by a scrub forest.
"That's the reason they have not been discovered for so long," said Funch. '' You can not see them in the native vegetation. And few scientists go through here. "
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