4,000-year-old termite mounds found in Brazil

Researchers have found a vast array of regularly spaced termite mounds in Brazil, which are about 4,000 years old and cover an area the size of Great Britain.

The mounds, which are easily visible on Google Earth, are not nests, according to the study published in the journal Current Biology.

They are the result of the insects' slow and steady excavation of a network of interconnected underground tunnels, researchers said.

The termites' activities over thousands of years has resulted in huge quantities of soil deposited in about 200 million cone-shaped mounds, each about 2.5 metres tall and 9 metres across.

"These mounds were formed by a single termite species that excavated a massive network of tunnels to allow them to access dead leaves to eat safely and directly from the forest floor," said Stephen Martin of the University of Salford in the UK.

"The amount of soil excavated is over 10 cubic kilometers, equivalent to 4,000 great pyramids of Giza, and represents one of the biggest structures built by a single insect species," Martin said.

"This is apparently the world's most extensive bioengineering effort by a single insect species," said Roy Funch of Universidade Estadual de Feira de Santana in Brazil.

"Perhaps most exciting of all -- the mounds are extremely old -- up to 4,000 years, similar to the ages of the pyramids," Funch said.

The mounds are largely hidden from view in the fully deciduous, semiarid, thorny-scrub caatinga forests unique to northeastern Brazil.

They would only really come into view by "outsiders," including scientists, when some of the lands were cleared for pasture in recent decades.

Soil samples collected from the centres of 11 mounds and dated indicated that the mounds were filled 690 to 3,820 years ago.

That makes them about as old as the world's oldest known termite mounds in Africa.

The researchers investigated whether the strangely regular spatial pattern of the mounds was driven by competition amongst termites in neighbouring mounds.

Their behavioural tests found little aggression at the mound level. That is compared to obvious aggression amongst termites collected at greater distances from one another.

The findings lead the researchers to suggest that the over-dispersed spatial mound pattern isn't generated by aggressive interactions.

Martin and his colleagues propose that the mound pattern arose through self-organisational processes facilitated by the increased connectivity of the tunnel network and driven by episodic leaf-fall in the dry forest.

They said that a pheromone map might allow the termites to minimise their travel time from any location in the colony to the nearest waste mound.

The vast tunnel network apparently allows safe access to a sporadic food supply, similar to what is been seen in naked mole-rats, which also live in arid regions and construct very extensive burrow networks to obtain food, researchers said.