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"  When red imported fire ants\u2014an invasive, stinging species found in the U.S. South and Southwest\u2014swarm, they do more than pool their strength and intelligence. The ants become a new kind of versatile material, one with the properties of both a liquid and a solid. Press down on a clump of ants and, rather than spreading out the way a liquid would, the ants compress like foam and then bounce back. But drop a dowel into a beaker of ants and they flow around it the way any liquid would. This state shifting has to do with the way the ants rearrange the connections of their many appendages, Georgia Tech biologist David Hu and his student Zhongyang Liu say in a study they presented today at the American Physical Society&amp;#039;s Division of Fluid Dynamics meeting in Pittsburgh.  The swarming of insects, like the flocking of birds and schooling of fish, is fascinating because these creatures\u2014which are not particularly capable as individuals\u2014can form a group that exhibits intelligent, organized behaviors such as flying in formation, scattering to avoid a predator, or, in the case of the fire ants, building watertight rafts. In addition, creating a superorganism from not-so-intelligent parts seems ideal for robotics. Belgian computer scientist Marco Dorigo of the Universit\u00E9 Libre de Bruxelles, for example, has used this swarm intelligence to create modular robots called swarm-bots, which self-assemble and work together. Studying fire ants, researchers say, could point the way to even better bots. Fire ants are an &amp;quot;organism that acts like a swarm but also like a material&amp;quot; Hu tells PopMech. &amp;quot;The ants are like molecules, but the molecules now have legs.&amp;quot; The interconnections among the legs are like the bonds between molecules, he says.  To investigate this ant material, the researchers used a sort of a press, called a rheometer, that measures how materials respond to applied forces. Live ants, they found, act like both an elastic solid, such as rubber, and viscous liquid, such as honey.  One way the ants make use of this skill is to assemble themselves into airtight rafts when their nests flood, as happens in their native Brazil. Researchers had previously found that within the raft, the ants connect via legs and jaws. One ant bites onto the leg of another, and they hold each other by their claws or connect by the sticky pads at the end of their legs. The arrangement of these interconnections is key to the ants&amp;#039; ability. When the scientists put dead ants in the rheometer, they found that the ants flowed less and were also less elastic, &amp;quot;like a pile of sand,&amp;quot; Hu says.  &amp;quot;By moving around, ants create a dynamic material that has unique properties,&amp;quot; Deborah Gordon, who studies collective behavior at Stanford, tells PopMech via email. &amp;quot;I&amp;#039;m looking forward to learning more about this. It demonstrates yet another technical advance, evolved by ants, that we hadn&amp;#039;t yet thought of.&amp;quot; And it&amp;#039;s another ant innovation that artificial intelligence researchers like Dorigo are keen to borrow. Hu says that studying the way these ants rearrange their connections also could help researchers to design self-healing materials. &amp;quot;In the last decade, the robotics community has shown a growing interest in the concept of self-assembly,&amp;quot; Mauro Birattari, who does research on swarm intelligence at the Universit\u00E9 libre de Bruxelles, tells PopMech via email. &amp;quot;I think that the results obtained by Hu could be relevant to the design of new kinds of robots. I see possible application in soft robotics and in nanorobotics.&amp;quot; "^^<http://www.w3.org/2001/XMLSchema#string>
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