Sinking Ant Towers
Jason Maderer July 11, 2017
If you want to see the Eiffel Tower, you don’t have to go to Paris. Just look down at your feet — but watch your step.
Fire ants use their bodies to construct Eiffel Tower-looking structures when they run into a tall obstruction while looking for food or escaping to new areas. A new study from the Georgia Institute of Technology suggests that they build these structures without a leader or coordinated effort. Each ant wanders around aimlessly, adhering to a certain set of rules, until it unknowingly participates in the construction of a tower several inches tall.
“If you watched ants for 30 seconds, you could have no idea that something miraculous would be created in 20 minutes,” said co-author David Hu, a professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “With no planning, and using trial-and-error, they create a bell-shaped structure that helps them survive."
How Towers Form
How they're built, how they sink, and where ants go.
The tower study is a follow-up to the group’s 2014 ant raft research, which examined how the insects link their bodies in order to build waterproof structures that stay afloat for months. The ants march along until they come to an open space — the edge of the raft — then settle in to become a building block of the raft.
They do the same thing for the towers, searching for an empty spot like a car in a crowded parking lot. Once an individual ant finds one, typically at the top of the tower, she stops and braces for more ants to climb on top and go vertical.
But vertical is a relative term. The ants don’t position themselves straight up and down like a skyscraper. Instead, the tower gets wider as it grows taller, gradually becoming the same shape as Paris’ iconic landmark. The weight of the tower is supported by a wider cross-section at its base, which allows the ants to better distribute their weight.
“We found that ants can withstand 750 times their body weight without injury, but they seem to be most comfortable supporting three ants on their backs,” said Craig Tovey, a co-author of the study and professor in the Stewart School of Industrial & Systems Engineering. “Any more than three and they’ll simply give up, break their holds and walk away.”