Then when the penny begins to sink through the group like they're a liquid; they'll let go of their grips on each other and move around the coin to fill in the void on top.
"Remarkably, the observed behavior is similar to what is seen in materials that are not alive, like polymer gels right at the point when they become a gel," said associate physics professor at Georgia Tech, Alberto Fernandez-Nieves.
In order to perform their experiments, the researchers dumped thousands of squirming fire ants into a rheometer - which is a device that's used to measure the flow of liquids or slurries (semiliquid mixtures, such as cement) anytime force is applied to them- and tested the effects of speeds from 0.0001 rpm to 100 rpm.
Once the speed got high enough, the live ants would give up their normal behavior and let go of one another to behave as though they were dead ants. This behavior decreased the viscosity of the group and allowed them all to flow more like a liquid.
"It's not unlike ketchup," explains Fernandez-Nieves. "The harder you squeeze, the easier it flows. But with ants, this happens much more dramatically than with ketchup."
Take a look at the incredible video below:
David Hu, an associate professor at Georgia Tech, explains that the behavior is a survival method. "Ants seem to have an on/off switch in that they let go for sufficiently large applied forces," he says. "Despite wanting to be together, they let go and behave like a fluid to prevent getting injured or killed."
Living in nature, ants will assemble their bodies into rafts in order to float and survive during a flood, and they can also form themselves into bridges to move across gaps. However, when forces are applied to ants, the group can act more like a malleable semi-liquid in order to avoid being crushed into an actual liquid.
"If you cut a dinner roll with a knife, you're going to end up with two pieces of bread," says Hu. "But if you cut through a pile of ants, they'll simply let the knife go through, then reform on the other side. They're like liquid metal - just like that scene in the Terminator movie."
Hu believes that this new research could be used to create a "self-repairing" material that can reform its original shape if it was to be broken or changed in some way. Try to image an army of T-1000 fire ants surging towards you. Then again, maybe you shouldn't!
This research group's findings were published in the journal Nature Materials recently. Pretty incredible right?! What do you think about their findings?
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It's fun to learn something new!