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Swarming Ants Behave Like Liquid Metal When You Squish Them

Swarming Ants Behave Like Liquid Metal When You Squish Them

You’ve probably smashed an ant or two in your day, but next time you do – remember what would happen if the ant was as big as you. The truth is, we’d be absolutely useless against most insects if they matched our mass. If you were as strong or able-bodied as an ant, you could run as fast as a racehorse and lift a Lamborghini Aventador over your head. But super strength isn’t the only trick ants have up their sleeves: they also behave like both a solid, and a liquid.

Fire ants didn’t start getting attention from physicists until 2013, when scientists at the Georgia Institute of Technology showed us how they moved through a funnel, behaving like some kind of thick, viscous goo. Now, they’ve taken things even further, stretching the ants’ abilities to the limit. What they found could be the future of material science – the key to unlocking self-healing materials.

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We all know that liquid flows – it’s something we encounter every day – but while most materials’ ability to do so is controlled by temperature (think water and ice), ant elasticity is controlled by the animals themselves. When they need to behave like a solid, say to raft across a river, they cling to one another. But those insect embraces can be broken and reformed when the group needs to flow.

“Imagine I had a glass window, and threw a brick through it,” says Georgia Tech Associate Professor David Hu. “But instead of having shards of window glass, imagine the window were made of some active material. The shards would allow the brick to pass, and reform to create a whole new window.”

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This is exactly what the ants are doing with this penny. Rather than being crushed by the force of the coin, they dissipate it by rearranging their bodies. This, the team explains, is another key property of liquids. “Ants are like liquid metal,” says Hu. “Just like that scene in the Terminator movie.” Or, you know, Alex Mack.

And interestingly, the viscoelasticity of the ants increases with their numbers. More ants, more stretch.

“Everything is a surprise [in this research],” adds graduate research assistant Michael J. Tennenbaum. “That the ants are viscoelastic is amazing. But perhaps the most amazing thing is that the behavior is reminiscent of inanimate materials; this we do not understand at all.” Think about ketchup, or polymer gels just before they solidify: like with the ants, the harder you squeeze, the easier they flow.

Beyond the penny test, the swarm was placed into a rheometer, a tool that measures the responses of various materials to force. It’s essentially a squish-test, but Tennenbaum assures us no ants were harmed in the making of this gif:

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“Ants are alive and like to explore,” he says. “As such, keeping them in one place long enough to measure can be a challenge. We had to add a containment cylinder to the rheometer to keep the ants in, but none of the tests hurt them.” The whole point of the test is to measure active groups of ants, meaning it doesn’t work on dead ones. As such, keeping the insects healthy was of utmost importance. “Some of the tests were limited not by the machine, but because too much pressure on the ants would shred them.”

Besides new materials, the team hopes their study will also lead to advances in robotics. Because ants are excellent co-conspirators, we can actually use their strategies to develop new rules for robots that have to work together. For example, a robotic swarm in flight.

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IMAGES: Georgia Tech

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