The common red fire ant, that spoiler of picnics worldwide, turns out to be one of the most talented engineers to be found in the animal realm, researchers say.
That engineering prowess is nowhere better demonstrated than when a fire ant colony under threat of flooding following heavy rain escapes by leaving its colony mound in mass numbers and, with each ant grasping its closest neighbor, assembling into an ant "raft" to safely float away.
The mystery of this "lifeboat" building behavior is that any single ant is denser than the water it's on and faces the possible risk of sinking and drowning. So how does a raft of thousands of the creatures manage to stay afloat?
Researchers at Georgia Tech found that in a typical fire ant raft, each ant is connected to 4.8 neighbors, using its six legs along with its mandibles and adhesive pads to create an average 14 connections.
Once connected, the ants extend their legs to increase distances between each individual.
"Increasing the distance keeps the raft porous and buoyant, allowing the structure to stay afloat and bound back to the surface when strong river currents submerge it," says researcher Nathan Mlot.
The ants are able to grab onto one another using their legs and mandibles with a force equal to 400 times their body weight, the researchers found.
Writing in the Journal of Experimental Biology, the scientists described how they analyzed the rafts by freezing some of them and scanning them in a CT scanner to look at the structure and connections within.
"Now we can see how every brick is connected," researcher David Hu says. "It's kind of like looking inside a warehouse and seeing the scaffolding and I-beams."
In addition to the connections larger ants in the raft make between themselves, smaller ants in the colony will fill spaces between the larger ones to prevent water from infiltrating the raft and to strengthen any weak points, the researchers found.
Determining the structure of ant rafts still doesn't explain how they know to create such constructions in the first place, they say.
"Fire ants are special engineers," Hu says. "They are the bricklayers and the bricks. Somehow they build and repair their structures without a leader or knowing what is happening. They just react and interact."
In addition to their raft-building expertise, fire ants, named scientifically as Solenopsis invicta, are best known to the public for their willingness to swarm and attack.
As any picnicker can tell you.
