Red fire ants build rafts out of their own bodies in order to cross bodies of water. Robots of the future may soon be able to learn some of the laws of self-assembly that guide these tiny insects, creating custom structures. 

When rains come to areas where the tiny animals make their homes, water streams into the subterranean nests. The ants stream out of their tunnels, and start clinging to one another. Eventually, they form into a raft, able to float on water. While each ant is heavier than water, and could sink, the large surface area of ants in a relatively flat plane provides buoyancy. 

Fire ants have also been seen using their bodies to provide temporary shelters, or bivouacs. When need, the tiny animals can link themselves together into towers and form spheres when they are twirled in a cup of water. 

David Hu from the Georgia Institute of Technology wanted to investigate how self-assembly could lead to various feats of engineering. He teamed up with Paul Foster and Nathan Mlot to see how ants carried out heir behavior. 

The team gently swirled 110 ants in a beaker, until they formed a sphere. They quickly froze the insects in liquid nitrogen, and sealed the formation with a vapor of instant glue. This structure was then examined in a CT scanner. This allowed the team to examine how individual ants were connected to each other. 

Months were spent examining the sphere of ants, studying hundreds of tiny limbs. The team found each ant used all six of its legs to grab onto other members, and was touched by an average of eight limbs from other individuals. 

"It turns out that 99% of the legs are connected to another ant and there are no free loaders," Hu said. 

Researchers found the tiny creatures aligned their bodies and legs in complex fashions, arranging themselves in perpendicular layers. When floating in water as a natural raft, they push against each other's bodies to lower the density of their crew, increasing buoyancy. 

It is still unknown how the ants know where to go or to whom they should cling. Understanding those rules could assist the creation of robots that build themselves into custom shapes, and infrastructure that repairs itself. 

"If ants can do it, maybe humans can create things that can too," Hu said. 

Investigation of red fire ants, rules of self-assembly, and how these may be allied to the development of robots was profiled in The Journal of Experimental Biology.