Four years ago, Ehud Fonio watched as pieces of his cat's dinner spontaneously floated from the feline's bowl. On closer inspection, he spotted an ant brigade: With the massive prize hoisted over their heads, they charged back to the nest.
Fonio, assistant staff scientist at the Weizmann Institute of Science in Israel, was witnessing the cooperative carrying of a load, which is surprisingly rare in the animal world. The ants in question are known as longhorn crazy ants, Paratrechina longicornis, owing to their seemingly crazed and nonsensical paths. And until recently, researchers couldn't understand how crazy ants navigated while carrying comparatively huge pieces of food to their nest.
The answer? A lot of cooperation and a bit of help from the ant version of an air traffic controller, according to a study published Tuesday in Nature Communications.
Researchers filmed groups of crazy ants zigging and zagging as they carried different-size loads nearly 100 times, tracking individual and collective motions. The scientists also added obstacles to the ants' path to test how well the group could navigate.
The "romantic view" of ants, explains Ofer Feinerman, an author of the study, is that each single ant is stupid, but together "emerges some kind of collective intelligence."
But "they're not stupid at all," says Feinerman, also a researcher at the Weizmann Institute of Science. (Also learn about: The Genius of Swarms.)
They found that the ants rotate jobs, alternating between carrying the load and "scouting out" the scene. If any scout ants notice their loaded down comrades drift off course, they grab hold and stubbornly push the disoriented group back on track. (Learn about more real-life animal superpowers.)
"The individuals come with the solution," says Feinerman. "The group gives it the muscle power."
This idea of individual knowledge dovetails with previous observations in bird flocks or fish shoals, "chipping away" at an intricate process, says David Hughes, an entomologist at Pennsylvania State University who was not involved in the research.
All for One, Usually
The researchers were surprised when they first started watching the crazy ants that the burdened critters never traveled straight for the nest—a meandering strategy that put the ants at risk of attack along the way.
By simulating the movements with a computer, the team discovered that the looping motion originated from the balance between independent and collective ant behavior.
A group of ants in which each member acts independently runs into trouble. Imagine carrying a couch with several friends: If everyone tried to lead the way, a game of tug-of-war would ensue. Even so, without any leaders, correcting for obstacles or wrong turns becomes impossible.
The ants stay on track by keeping their roles fluid.
Each leader's role is short-lived and may last only 10 to 15 seconds, explains Feinerman. After that, the leader loses its sense of direction and becomes one of the crowd, and other carriers detach to scout.
The Tipping Point
Most importantly, as the group grew, the ants became less independent.
"There's a goldilocks size," says Vijay Kumar, a mechanical engineer at the University of Pennsylvania who studies collective animal behavior for robotic applications. (Also learn about self-organizing robots.)
When groups are very small—just a couple of ants—each ant fights for a different direction and doesn't get anywhere. But if the group is too large, the ants can't navigate around obstacles. "Too many cooks spoil the broth," says Kumar, who was not involved in the research.
The ants "do it even better than us," says Feinerman. Ants can coordinate huge groups, but "if you let 100 people carry something together, I don't think they would get far."
Rachel Becker contributed to the research for this story.
Follow Maya Wei-Haas on Twitter