A "wonder of the Earth", the size of Minnesota, was built by termites in Brazil

In northeastern Brazil, in a forest so dry that trees are bleaching, termites have been at work for millennia. The only outward signs of their work are mounds of dirt, dumps of waste from their underground excavations. Dirt and garbage usually arouse as much admiration as toenail clippings – but they are real piles of slag.

The conical mounds, each about 8 feet tall and 30 feet wide, emerge from the ground at regular intervals, spaced about 60 feet from each of the six neighbors. From the air, the pattern evokes a checkerboard or hexagonal combs from a hive. A satellite map, via Google Earth, indicates that the mounds cover an area of ​​more than 88,000 square kilometers, an area larger than Minnesota.

"Imagine it's a city," said Stephen J. Martin, an entomologist and expert on social insects at the British University of Salford. "We have never built a city so big." And the termites, centimeter long, Syntermes dirus, did it grain by grain.

In total, termite excavated soil is equivalent to the volume of 4,000 pyramids in Giza, as reported by Martin and his co-authors in a study published in Current Biology on Monday. They sampled the mound centers and, by measuring the radiation in the mineral grains, determined that the oldest mound tested was about 3800 years old. Maybe others are older. On the basis of satellite images and spot checks over thousands of kilometers, scientists estimate that 200 million mounds scattered throughout the landscape.

If the forest cover disappears, exposing the mounds in all their splendor, this place would be celebrated as a "wonder of the Earth," said Martin.

Yet, hidden under trees and thorny bushes, mounds can be difficult to spot. Martin did not notice them at first. He had gone to the Brazilian dry forest, called the caatinga, in search of honeybees. After only miles of driving, where the road cut through the trees to reveal the form of gum drop mounds, he saw them. These were termites, the locals told Martin.

"No, it can not be true – there are too many," he remembered, thinking. Back in Britain, colleagues told him that the mounds had to be lake sediments or some other geological feature.

The locals, of course, were right, as Martin discovered on his return. A few miles from a big city, while walking near a swimming pool, the entomologist stumbled upon another biologist, Roy Funch.

"He was walking down the river with a friend and I went up the river to go swimming," said Funch, co-author of the new newspaper. Martin "obviously looked like an outsider," said Funch, who also works as a tour guide, praised and asked what had brought Martin to Brazil. The termite mounds, said Martin, lamenting that nothing was found in Google Scholar.

"I said," Hey, you just met the only guy in Brazil who works on these mounds, "recalls Funch." So, you know, 'happy'. says it lightly. "

Funch went to Brazil in the 1970s with the Peace Corps. The beautiful mountains and hiking trails have persuaded him to settle in the north-east of the country, he said. He also fell in love with mounds. The largest, which Funch calls "grandmother's mounds", reaches 15 feet in the air. (Not everyone is active yet.)

"I do not think anyone has ever seen such a scale change on such a scale by such small creatures," he said.

In the 1980s, Funch, who describes himself as an "underwater scientist" but holds a PhD in botany, wrote about termites for a popular science magazine. He hoped to attract the attention of other researchers. Nobody Thirty years passed and he decided to study them himself, until he teamed up with Martin.

These mounds, unlike hives built by other termites, are neither nests nor ventilation shafts. "We thought the nests would be in the middle of the mounds," said Funch. "They were not there, they were not even under the mounds." A single large tunnel of about 10 centimeters in diameter passes through the center of the mound. Termites deliver their waste and close the tunnel at the top.

"Nobody has ever found the nests of queens, we really do not know what's going on underground, absolutely nothing," Funch said.

Mounds are uncooperative subjects. Soldier termites appear when researchers disturb the dirt. They will run the blood, said Martin. "They have very sharp mandibles, they will cut the skin," he says. Nutrient-poor soil is a nightmare to dig, cooked like concrete under heat.

Distance and poor soil are the qualities that allow termites to last. The region has long periods of drought, said University of Buffalo geographer Eun-Hye Yoo, author of the study. (Yoo also met Funch in a Brazilian tourist town. "It's a good place to meet people," he said.) The climate, even though it's not conducive to human agriculture, is stable. In this hostile environment, the termite kingdom blossoms.

"These termites have exploited this area and have done very well," Martin said.

The rainy season lasts about a month. The caatinga jumps from brown to green then comes back. Trees flourish and lose their leaves as quickly. In a few weeks, the forest floor is stripped of any leaves. Termites take everything to eat. Martin suspects that litter supports them during the rest of the year. Termites elsewhere grow fungi on leaf litter, but there are no known fungus-growing termites in South America.

Scientists have no definitive explanation for the unusual hexagonal spacing of mounds. The model is "absolutely striking and quite unusual in its scale, and it is a fine example of large-scale self-organization," said Corina Tarnita, a mathematical biologist at Princeton University. did not participate in the new job. The only comparable reason in nature that is so widespread, she said, are the African fairy circles, rings in the brush that appear from Angola to South Africa.

But Martin proposed that, as these social insects "are very, very good in optimization", the six-pointed system could be the most effective. Under the dirt, as evidenced by the fiber optic cable, is a large interconnected tunnel system. Termites are guided by pheromones, the insect equivalent of a subway driver.

"When you have enough connections, it is very easy to find the nearest mound," Martin said. Only if a mound does not exist at the edge of the megalopolis will they start building a new one.

Tarnita warned that the mounds tested in this study were randomly made. "It would really be important to have a systematic assessment of age that gives an idea of ​​the relationship between the age of a mound and that of its neighbors, or neighbors of its neighbors. "she said.