From: Debra Goldberg, ENN
Published November 26, 2013 03:03 PM

Fire-ant rafts inspiring materials science research

In our highly digital world, people often forget about the natural wonders around us and the importance they serve in our everyday lives. When taking a closer look, nature is oftentimes the best model for advancing our technology. Plants have taught us the importance of light energy, and now insects are sparking ideas in materials science.



The fire-ant, an insect feared for its stinging, venom-injecting bite, is being studied for its "viscoelastic" properties. Viscoelastic materials not only resist shear flow and strain when a stress is applied, like honey, but also bounce back to their original shape when stretched out or compressed, like rubber bands. Therefore, these materials are neither solid nor liquid, but a combination of both, like Jell-O and toothpaste. Fire-ants form rafts in the presence of any forceful liquid, but not just any typical ant raft. These rafts actively reorganize their structure. This allows them to more effectively cushion themselves against applied forces, such as raindrops or wave surges. 

Study lead, Zhongyang Liu, an undergraduate student at Georgia tech, working with mechanical engineer and biologist, David Hue, has found that fire ants form their rafts by linking their legs and jaws. "The linkage structure they form, similar to a truss structure, is elastic and so is able to sustain external forces," Liu said. 

This new study, to be presented in a talk at the upcoming American Physical Society's Division of Fluid Dynamics (DFD) meeting in Pittsburgh, Pa., notes that the structure of an ant raft is far from stationary. "It is in constant flux because the ants repeatedly form, break, and reform their body-part connections. Through these rearrangements, the researchers discovered, the raft is able to store energy (and thus acts as an elastic material) and dissipate energy (as a viscous material) to equivalent degrees — a situation that has not been seen in any other active materials, such as bacteria films or liquid crystals. (Indeed, the researchers found, rafts made of dead ants don't show this feature; instead, they behave more like solid viscoelastic materials)."

These findings play an unusual role in the world of engineering. According to Liu, "This is our most important discovery" because the swarm intelligence that the ants use to accomplish their continual construction could be applied to robotics research. Furthermore, he added, "the special structure formed by the ants might inspire new research in material science."

Read more from American Physical Society

Fire-ant raft image via NPR

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