COLUMNS of workers penetrate the forest, furiously gathering as much food and supplies as they can. They are a massive army that living things know to avoid, and that few natural obstacles can waylay. So determined are these legions that should a chasm or gap disrupt the most direct path to their spoils they simply build a new path--out of themselves.
Without any orders or direction, individuals from the rank and file instinctively stretch across the opening, clinging to one another as their comrades-in-arms swarm across their bodies--but this is no force of superhumans. They are army ants of the species Eciton hamatum, which form "living" bridges across breaks and gaps in the forest floor that allow their famously large raiding swarms to travel efficiently.
Researchers from Princeton University and the New Jersey Institute of Technology report that these structures 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 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.
"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," says co-first author Matthew Lutz, a former graduate student in Princeton's Department of Ecology and Evolutionary Biology.
"There's no single ant overseeing the decision; they're making that calculation as a colony. Thinking about this cost-benefit framework might be a new insight that can be applied to other animal structures that people haven't thought of before."
The research could help explain how large groups of animals balance cost and benefit, about which little is known, relates 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 Germany's University of Konstanz.
Previous studies have shown that single...