A writhing mass of fire ants floating across the water is thing of horror and a marvel of engineering. But how do you study the architecture of ever-squirming ants? By flash-freezing them and coating in glue, as scientists did for a recent study. Ant rafts, it turns out, are more complicated than you might think, and they could one day help us building smart, self-assembling robots.
In nature, rainy weather causes fire ants to pour out of their nests and link together to make floating rafts as big as dinner plates. It is, as Nature puts it, a real "feat of social cooperation and biophysics." David Hu and his team at the Georgia Institute of Technology found they could get ants to form these rafts by just pouring the creatures into a cup and stirring — no water needed. Then came the liquid nitrogen and the glue, which permanently bonded the ants together into a still mass that could be 3D scanned.
The structure of the ant rafts is actually quite incredible to contemplate: Each ant is connected to an average of 14 others, with some ants connected to as many as 20. "It turns out that 99% of the legs are connected to another ant and there are no free loaders," said Hu. The ants had also consciously oriented their bodies perpendicular to one another, creating an interconnected and lightweight structure. The raft is at once water-repellant and light enough to float.
Not bad for creatures with pretty tiny brains; maybe tiny robots could take that cue. Robot designers envision a colony of little robots that can connect to one another and self-organise into different shapes like these ants. Human-designed robots tend to be strictly geometric, but the loose lattice of ants suggest more an organic organisation can also work. Fire ants, after all, have done a pretty good job of invading the world. [Journal of Experimental Biology via Nature]