Fire Ants Use Ancient Jungle Survival Skills to Ride Out Recent Rains
A scene out of the Brazilian rainforest played out in a Fairhope puddle as fire ants native to the Amazonian jungle relied on an ancient trick to survive early June’s deluge.
After their nest was submerged under several inches of water in a park, the ants managed to create a floating raft composed only of their bodies. Chained together in a network of interlocking legs, bodies and mandibles, the entire colony drifted around on the surface of the puddle.
Crawling atop the writhing mass, worker ants could be seen carrying white larvae and the slightly more developed pupae of their young, rescued from the nursery areas of the sunken colony. Giant soldier ants, perhaps three times larger than the workers, marched back and forth across the top of the living vessel like sea captains surveying the horizon. And every now and then, the queen would emerge from the center of the mass, surrounded by thousands of her minions.
Scientists studying fire ants in their native Brazil have spent years puzzling over the ability of enormous colonies there to form floating lifeboats several feet across. In the frequently inundated bottomlands surrounding the Amazon, the ants have been known to float for months at a time. The mystery lies in the fact that ants are heavier than water, and a lone ant quickly sinks. How then do thousands of ants manage to stay afloat?
Working in the Hu Biolocomotion Laboratory at the Georgia Institute of Technology, David Hu and his fellow researchers solved the mystery. Locking together “tarsus to tarsus,” Hu wrote in a scientific paper published in 2011, the network of ant bodies and legs forms a sort of waterproof fabric.
“The ants are basically a waterproof surface the world hasn’t seen before … it is a great mechanism to deal with a deluge, one that took millions of years to evolve,” Hu said in a Tuesday interview. “It is the same principle that Gore-tex works on. It’s highly porous fabric that has lots of air pockets. The water has to do a lot of work to penetrate the fabric.”
To study the ant rafts, Hu froze the ants with liquid nitrogen and analyzed how they were joined together under an electron microscope. Tiny hairs all over the legs of the ants served to make the living waterproof fabric they created even tighter. In addition to keeping water out, those hairs and ant bodies worked to trap tiny air bubbles beneath each ant.
Those bubbles joined together beneath the raft, increasing its buoyancy, and ensuring that none of the ants die, even those buried on the bottom of the raft. Hu filmed the ants forming the rafts and filmed a scientist pushing down on top of a raft with forceps. Incredibly, the forceps were able to push a portion of the raft more than an inch underwater without it breaking apart, and without leaking. A bubble of air can be seen surrounding the ants in the video.
“Our intuition of water doesn’t hold at small scales. Water acts like a trampoline on the scale of ants,” Hu said. “The ants are surprisingly elastic. They can build these membranes that are quite strong. The water doesn’t penetrate the ants, which boggles our expectations.”
Hu said the research is applicable in the cutting edge field of modular robotics.
“Robots of the future will have a big bucket of parts. You dump them out and assemble a machine” purpose-built for the job at hand, Hu said.
“Ants are like that. There are millions of parts. They can assemble into something, like a raft, or a bridge, and do it without central control.”
Hu’s research lies at the nexus of engineering and biology. For a time, his focus was on insects that walk on water, such as water striders. A device constructed in his lab out of a 7-Up can and elastic from a tube sock can walk on water. Called the Robo Strider, it weighs less than a postage stamp.
“I’m interested in the biology, but also what animals can do to show us how this kind of behavior is possible,” Hu said. “Clearly we can build machines that outperform nature in some respects – airplanes and cars, for instance – but other challenges, things like linking together and cooperating, we don’t have a clue how to build a machine that can do those things.”
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