The ants manage this coordination with no leader and with minimal cognitive resources. An individual army ant is practically blind and has a minuscule brain that couldn’t begin to fathom their elaborate collective movement.

“There is no leader, no architect ant saying, ‘We need to build here,’ ” said Simon Garnier, director of the Swarm Lab at the New Jersey Institute of Technology and co-author of a recent study that predicts when an army ant colony will decide to build a bridge.

Garnier’s study helps explain not only how unorganized ants build bridges, but also how they pull off the even more complex task of determining which bridges are worth building at all.