Researchers from Princeton University and the New Jersey Institute of Technology (NJIT) report for the first time that army ants of the species Eciton hamatum that form “living” bridges across breaks and gaps in the forest floor are more sophisticated than scientists knew. The ants exhibit a level of collective intelligence that could provide new insights into animal behavior and even help in the development of intuitive robots that can cooperate as a group, the researchers said. Ants of E. hamatum automatically form living bridges without any oversight from a “lead” ant, the researchers report in the journal Proceedings of the National Academy of the Sciences. The action of each individual coalesces into a group unit that can adapt to the terrain and also operates by a clear cost-benefit ratio. The ants will create a path over an open space up to the point when too many workers are being diverted from collecting food and prey.
The researchers suggest that these ants are performing a collective computation. At the level of the entire colony, they’re saying they can afford this many ants locked up in this bridge, but no more than that. There’s no single ant overseeing the decision, they’re making that calculation as a colony. The research could help explain how large groups of animals balance cost and benefit, about which little is known, said co-author Iain Couzin, a Princeton visiting senior research scholar in ecology and evolutionary biology, and director of the Max Planck Institute for Ornithology and chair of biodiversity and collective behavior at the University of Konstanz in Germany. Previous studies have shown that single creatures use “rules of thumb” to weigh cost-and-benefit, said Couzin. This new work shows that in large groups these same individual guidelines can eventually coordinate group-wide — the ants acted as a unit although each ant only knew its immediate circumstances, he said.