STARTED FROM THE BOTTOM

Fire ants can build complex towers to get out of trouble

Some of the biggest scientific discoveries happen by accident. Velcro, X-rays, pace makers, vulcanized rubber—all were discovered by chance. Some of the smallest discoveries happen by accident too. Ant-sized ones.

Scientists at Georgia Tech were trying to figure out how ants built themselves into towers to escape confinement or danger. They put a small pole in the middle of a dishful of ants and filmed what happened. The ants, they found, climb upwards, on top of each other, until they find an empty spot. Then they stop. The next one does the same, and so on.

Despite being able to lift 750 times their weight, each ant only supports three others above them. The researchers don’t believe the ants are doing this intentionally. But accidentally or on purpose, what’s created is a “tower of constant strength” where each ant in the tower is bearing the same load. (The resulting tower looks a little bit like the famous one in Paris, designed by Gustave Eiffel.)

“With no planning, and using trial-and-error, they create a bell-shaped structure that helps them survive,” said co-author David Hu, a professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering.

But then a curious thing happens. As more ants pile on, the ants in the middle sink lower, then climb out the bottom before restarting their journey back to the top.

Why the ants constantly rebuild the tower, researchers aren’t entirely sure—but they almost missed this crucial piece of information. They had planned to record ants building for two hours, but the camera rolled for three. Speeding through what they thought was an extraneous hour, the team was startled to get a different view of what was actually going on.

“We didn’t expect to see anything interesting in that extra hour, so we sped up the video to 10 times real speed,” said Craig Tovey, also a co-author of the study and professor at the Stewart School of Industrial & Systems Engineering at Georgia Tech.

“We were amazed at how different the ant movements appeared.”

The ants’ construction methods could be used to program modular robots to turn themselves into towering structures. Right now robots aren’t very good at building upwards, but the patterns the ants make in their tower building could be a solution.

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