Newspaper article The Christian Science Monitor

How Army Ants Use Their Own Bodies to Build Efficient Bridges

Newspaper article The Christian Science Monitor

How Army Ants Use Their Own Bodies to Build Efficient Bridges

Article excerpt

A gap in an ant's path might be a daunting obstacle for the insect's small body. But army ants in tropical forests of Central and South America work together to make shortcuts.

Linking their bodies together, the army ants build bridges for their comrades to march across.

That sounds like smart cooperation, but the ants go beyond that. Researchers have found that the ants seem to weigh the costs and benefits of making long, living bridges. If a shorter distance requires too many ant bodies, the ants appear to decide that it's not worth it, according to a paper published Monday in the journal Proceedings of the National Academy of Sciences.

Army ants frequently build bridges beginning at the intersection between sticks, vines, or other material the insects are walking on. They continuously inch the bridge along a gap, adding more bodies in order to span a larger and larger space and make a more efficient route.

This new research finds the bridge stops moving when the ants sense they are actually slowing their progress overall by using so many bodies.

"This stopping was a complete surprise for us," study co-lead author Christopher Reid said in a news release. "In many cases, the ants could have kept the bridge moving to create better shortcuts, but instead they stopped before achieving the shortest route possible."

"These bridges change dynamically with the traffic pattern on the trail," Dr. Reid said. "Imagine if the George Washington Bridge between New York City and New Jersey would reposition itself across the river depending on the direction of rush-hour traffic."

To observe the army ants in action, Reid and colleagues put boards down on the rainforest floor, creating an angular gap in the ants' path. Sure enough, they saw the ants one-by-one use their bodies to build and extend a bridge.

When new ants added their bodies to the collective bridge, they chose to be on the side of the bridge furthest from the crook in the gap. …

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