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Mound fields. The mounds are found in dense, low, and dry vegetation of the caatinga forest and can be seen when the land is cleared for pasture. Credit: Roy Funch
The researchers reporting in Current biology On November 19, Northeast Brazil discovered a wide range of regularly inhabited and still uninhabited termite mounds, covering an area the size of Britain, about 4,000 years old.
Mounds, easily visible on Google Earth, are not nests. They result rather from the slow and regular excavation by insects of a network of interconnected underground tunnels. The activities of termites for thousands of years have resulted in the formation of enormous amounts of soil in about 200 million cone-shaped mounds, each about 2.5 meters high and 9 meters wide.
"These mounds were formed by a single termite species that dug a huge network of tunnels to allow them to access dead leaves to eat safely and directly from the forest floor," said Stephen Martin. from the University of Salford in the United Kingdom. "The amount of soil excavated exceeds 10 cubic kilometers, or the equivalent of 4,000 large pyramids of Giza, and represents one of the largest structures built by a single species of insect."
"It's apparently the world's largest bioengineering effort for a single species of insect," adds Roy Funch of the Universidade Estadual de Feira de Santana in Brazil . "Perhaps the most exciting of all – the mounds are extremely old – up to 4000 years old, similar to the age of the pyramids."
Mound fields. The mounds are found in dense, low, and dry vegetation of the caatinga forest and can be seen when the land is cleared for pasture. Credit: Roy Funch
Mounds are largely hidden from view in the entirely deciduous, semi-arid and thorny caatinga forests unique to northeastern Brazil. They were really visible only by "strangers", including scientists, when some of the land was cleared for pasture in recent decades.
Soil samples taken from mound and dated centers indicated mounds were filled 690 to 3820 years ago. This makes them about as old as the world's oldest termite mounds in Africa.
Researchers investigated whether the oddly regular spatial pattern of mounds was dictated by competition between termites of neighboring mounds. Their behavioral tests revealed little aggressiveness at the mound level. This is compared to the obvious aggression among termites collected at greater distances from each other.
The results led the researchers to suggest that the overly dispersed spatial mound model is not generated by aggressive interactions. Instead, Martin and his colleagues propose that the mound model results from self-organizing processes facilitated by the increased connectivity of the tunnel network and driven by an episodic foliar drop in the dry forest.
Mound fields. The mounds are found in dense, low, and dry vegetation of the caatinga forest and can be seen when the land is cleared for pasture. Credit: Roy Funch
They say that a pheromone map could allow termites to minimize their travel time from anywhere in the colony to the nearest garbage mound. The extensive network of tunnels apparently provides safe access to a sporadic food source, similar to that seen in naked mole rats, which also live in arid regions and build extensive burrows for food, report Researchers.
"It's amazing that today we can find an" unknown "biological wonder of this size and age, with occupants always present," said Martin.
The researchers say that there are still many questions to ask. For example, no one knows how these termite colonies are physically structured because a queen chamber of the species has never been found.
Explore further:
Climate control in termites
More information:
Current biology, Martin et al .: "A vast spatial pattern of 4000-year-old termite mounds", DOI: 10.1016 / j.cub.2018.09.061
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