#army ant

Marching through the forest in colonies up to a million strong, army ants are some of the most formidable predators on the planet. Their extraordinary collective behaviour gives them the power to overcome almost any obstacle that gets in their way - including seemingly uncrossable gaps along their trail. By grabbing hold of each other’s bodies, the ants are able to form ‘living bridges’ that can allow thousands of their fellow colony members to safely cross, reducing the time and energy that would be lost by instead having to find a way around the gap. New research on the species Eciton hamatum in Panama has found that the creation of these bridges is much more dynamic than previously thought. The ants will initially build the bridge at the narrowest possible crossing point, but will then extend and move the bridge by adding more individuals to help create the shortest possible route. However, every worker that is taken up in forming a bridge is one less that will be performing other important tasks such as foraging for food. The bridge therefore stops moving and lengthening when the costs of adding more individuals outweighs the benefits of shortening the trail, and eventually dismantles when the number of ants crossing the bridge becomes low.

Ref: Reid C. R. et al., 2015. Army ants dynamically adjust living bridges in response to a cost–benefit trade-off. PNAS[link]