How fire ants form giant rafts to survive Houston floods

Craig Tovey is Professor of Industrial & Systems Engineering and Co-Director of the Center for Biologically Inspired Design at Georgia Institute of Technology

Drop a clump of 100,000 fire ants in a pond of water — or flood a huge area of Texas that’s infested with fire ants and drive them out of their nests in large groups. In minutes the clump will flatten and spread into a circular pancake that can float for weeks without drowning the ants.

Drop the same clump of ants near a plant on solid ground.

They’ll climb atop each other to a form a solid mass around the plant stem in the shape of the Eiffel Tower — sometimes as high as 30 ants tall. The ant tower serves as a temporary encampment that repels raindrops.

How and why do the ants make these symmetrical but very different shapes? They depend on touch and smell — not sight — to perceive the world, so they can sense only what’s very close to them. Contrary to popular belief, the queen doesn’t issue orders to the colony; she spends her life laying eggs. Each ant controls itself, based on information gathered from its immediate vicinity.

As both a systems engineer and biologist, I’m fascinated by the ant colony’s effectiveness in diverse tasks, such as foraging for food, floating on water, fighting other ants and building towers and underground nests – all accomplished by thousands of purblind creatures whose brains have less than one ten-thousandth as many neurons as a human’s.

In earlier research, my colleague David Hu and I investigated how these tiny creatures weave their bodies into water-repellent lifesaving rafts that float for weeks on flood waters. (This didn’t happen after Katrina flooded New Orleans in 2005 because the storm surge and levee collapses happened so fast the ants couldn’t escape their nests, and drowned. Harvey’s…

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