THE ants may go marching one by one, but they end up forming a superstructure of thousands and together they can form a raft that stretches the boundaries of the laws of physics, according to new research released today. Ants have exoskeletons that are naturally hydrophobic, or water repellant. A single ant can walk on water because of the buoyancy of the air bubbles trapped next to its body, and the waters own surface tension. However, when thousands of ants stand on top of each other, their multiplied weight should cause them to sink. But for years, biologists have observed fire ant colonies floating down flood plains and rivers in their native South America. For the first time, a group of engineers has attacked the question of ant flotation from a physics perspective. Ants float as a group because they can harness the power of nearby air bubbles. Grasping each others mandibles or front legs with a force 400 times their body weight, the ants are able to trap small pockets of air between them like a group floatation device. The ants are so tightly knit together, that air pockets form between the water and the ants, and water cannot penetrate through any part, said Nathan Mlot, a graduate student at the Georgia Institute of Technology in Atlanta and one of the studys authors. The bottom layer of ants rests on top of the waters surface, and others pile on above them. Even when they do get submerged, the pockets of air bring them back to the surface quickly and allow them to breathe. When they get submerged, the ants flex their muscles in unison to form a tighter weave. To understand exactly how the structure worked, the researchers took a raft of several thousand ants and dropped it in liquid nitrogen, immediately freezing it. Then they were able to look at the structure on an ant-by-ant level under an electron-scanning microscope. We were surprised at just how waterproof raft was its ability to repel water and keep afloat, said Mlot. Fox New