The mystery behind the remarkable ability of fire ants to turn themselves into a living, crawling life raft has been unlocked by scientists: The insects use air pockets that form around their bodies to protect themselves from drowning.
The analysis, published online Monday in the journal Proceedings of the National Academy of Sciences, could one day provide a useful model for building robots that can perform complex functions quickly and cooperatively, the study authors said.
Fire ants, named for the burning sting left by their bites, possess incredible powers of floatation when they work together, turning themselves into life rafts that can survive flash floods in their native Brazilian rain forests and travel for months before making landfall.
"They bring out the eggs, the young ants and provisions -- everything that happens to be in their mandibles at the time -- " and carry them onto rafts made of their own bodies, said lead author Nathan Mlot, a third-year doctoral student in the mechanical engineering department at the Georgia Institute of Technology in Atlanta.
But no one knew how these insects, which flounder and struggle in the water as individuals and whose bodies are denser than water and thus should sink, could float when they banded together.
To catch the ants in action, researchers collected fire ants off roadsides in Atlanta and brought them to their lab. The ants, they knew, behaved like a fluid: A handful could be molded and even poured. So the scientists swirled the ants in beakers until they formed spherical clumps, then dropped those ant balls into containers of water.
Quickly, the ants spread out into a pancake-like formation, forming rafts. The researchers froze one of the ant rafts with liquid nitrogen and studied its composition under an electron microscope. They observed that the ants had used their claws, adhesive pads on their legs and their mandibles -- pincer-like jaws -- to grip onto one another.
"At first it just looks like a tangle of bodies and limbs everywhere, but the longer you look at the picture, the more you're able to distinguish between different body parts and see the connections," Mlot said.
At such a high -- and perhaps unflattering -- resolution, the researchers also noticed how hairy the ants' water-repelling bodies were. Those hairs allowed the insects to trap air bubbles. With so many ants jammed together, their individual bubbles fused to form a protective air layer for all of them.
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