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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 driving in these places and I started saying," What are they? " Said Dr. Martin, an entomologist at the University of Salford in England. was in Brazil for research on the global decline of bees.
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."
Dr. Martin recalled his incredulous response: "And I went," Are you really sure of that? "And they're like," Well, I do not know, I think so. "
On a later trip, Dr. Martin met Roy R. Funch, an ecologist at the Brazilian State University of Feira de Santana, who was already planning a 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."
Dr. Funch also underestimated.
How many mounds? About 200 million, say the scientists.
"They are everywhere," said Dr. Funch.
The cone-shaped mounds are the work of Syntermes dirus, one of the largest termite species 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 have never built a city as big, anywhere else," said Dr. Martin.
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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. "It just threw me out of the water," Dr. Funch said.
Dr. Martin stated that they had used the minimum age suggested by the data, but that the oldest mound could possibly be more than twice as old.
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 mounds
Other termites build mounds with intricate networks of tunnels providing ventilation to underground nests.
But, cutting through some of the mounds, Doctors Funch and Martin found only one central tube leading to the top and they never came across nests.
These mounds were not ventilation structures, but simply piles of earth. While termites were digging networks of tunnels below the landscape, they needed a place to get rid of the excavated soil. So they carried the dirt in the central tube up to the top of a mound and threw it away.
This could also explain the regular spacing between mounds. At first, Dr. Funch and Dr. Martin thought it was the result of competing colonies. But when they put a termite of a mound next to another of a nearby mound, there was no conflict, which indicates that they belonged to the same family.
They concluded that the model was simply an efficient separation of waste piles.
According to Dr. Funch, young active mounds reach 4 to 5 feet in height. 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.
While locals knew about termites, few foreigners knew it. The extent of termite construction was hidden by a scrub forest called caatinga.
"That's why they have been unknown for so long," said Dr. Funch. "You can not see them in the native vegetation. And few scientists go through here.
For most of the year, with temperatures up to 100 degrees Fahrenheit or warmer, the trees are burned with white. The landscape becomes green after a short rainy season, then leaves fall and the landscape becomes desolate again.
"These termites live on dead leaves and feed once a year," said Dr. Martin.
As parts of the forest were cleared, the mounds became visible, and about a decade ago Google Earth's satellite imagery became clear enough for Mr. Funch to spot individual mounds. He went to some sites to check that the mounds were there.
Dr. Martin stated that he wanted to better understand the interrelation between insects and vegetation. When a part of the forest is cut, the mounds remain, but the termites move away because there is no leaves left to eat.
They also want to observe termites during the feeding season after the forest has blossomed and to study what termites do for the rest of the year.
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