Metropolis of termite mounds was hidden in plain sight

Stephen J. Martin noticed large mounds, some 10 feet tall, 30 feet wide, along the side of the road as he drove through a remote part of northeast Brazil.

“After 20 minutes, we were still driving through these, and I started saying, ‘Well, 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 they might be piles of dirt displaced from the construction of the road. Instead, his companions told him, “Oh, they’re just termite mounds.”

Martin recalled his incredulous reply: “And I went, ‘You’re really sure about that?’ And they’re like, ‘Well, I don’t know. I think so.”’

On a subsequent trip, Martin met Roy R. Funch, an ecologist at Brazil’s State University of Feira de Santana who already was arranging to conduct radioactive dating to determine the age of the mounds.

“I said, ‘Look at those, there must be thousands of these mounds. And he went, ‘Nah, there’s millions.”’

But Funch had undercounted.

In research published in the journal Current Biology, Martin, Funch and their colleagues report the findings from several years of investigations.

How many mounds? Some 200 million, the scientists estimate.

The cone-shaped mounds are the work of Syntermes dirus, among the largest termite species: They’re about a half-inch long. The mounds, spaced on average about 60 feet apart, are spread across an area as large as Britain.

“As humans, we have never built a city that big, anywhere,” Martin said.

The scientists also were surprised when they received results of the radioactive Researcher Roy Funch stands in a vast field of termite mounds, now estimated by ecological researchers to number about 200 million, in a remote area of Brazil. Researchers say it’s the greatest known example of ecosystem engineering by a single insect species.

dating of 11 mounds. The youngest was about 690 years old. The oldest was at least 3,820 years old, or close in age to the great pyramids of Giza in Egypt. “That just kind of blew me out of the water,” Funch said.

The scientists also estimated that to build 200 million mounds, the termites excavated 2.4 cubic miles of dirt — a volume equal to about 4,000 great pyramids of Giza. “This the greatest

known example of ecosystem engineering by a single insect species,” the scientists wrote.

Another surprise was that the mounds turned out to just be mounds.

Other termites build mounds with complicated networks of tunnels that provide ventilation for underground nests.

But cutting through some of the mounds, Funch and Martin found only a single central tube leading to the top, and they never came across any nests.

These mounds were not ventilation structures, but simply piles of dirt. As the termites excavated networks of tunnels below the landscape, they needed somewhere to discard the excavated dirt. So they carried the dirt up the central tube to the top of a mound and tossed it out.

Young, active mounds grow to 4 to 5 feet tall in a couple of years, Funch said. Most of the older mounds appear inactive. The scientists do not know if that means the termites have left or if they simply have no need for additional digging in the area after constructing the needed tunnels.

Though people living in the region knew of the termite mounds, few outsiders did. The expanse of the termites’ construction was hidden by scrubby forest.

“That’s why they were undiscovered for so long,” Funch said. “You cannot see them in the native vegetation. And not many scientists pass this way.”