Anyone who has watched ants scurrying purposefully along the ground to deliver food to their nest might have wondered whether the industrious insects ever face traffic control problems. Audrey Dussutour, Jean-Louis Deneubourg and Vincent Fourcassié are fascinated by collective motion in these social insects, and decided to see how black garden ants cope with bottlenecks(p. 2903).
To investigate traffic dynamics in ants, the team set up twelve experimental `ant nests' and lured the insects to a tasty sugar solution a short distance away. Some ants had to cross a wide bridge to get to the food,but others had to cross a bridge with a narrow bottleneck. The team filmed the ants marching to and from the sugar solution and analysed the video frames to calculate how long it took ants to travel from the nest to the food, as well as the number of head-on collisions between the ants. The team was surprised to find that ants somehow maintained the same rate of food delivery to the nest on both bridges, despite the bottleneck.
How did the ants maintain traffic flow on the narrow bridge? The team realised that, rather than battling their way through the crowds, ants patiently wait for their turn; neatly alternating groups of food-bound and nest-bound ants crossed the bottleneck. This reduces the number of head-on collisions on the narrow bridge, enabling ants to cross this bridge as quickly as the wider bridge. The team notes that this behaviour might prevent congestion in ant nest tunnels – and on our streets! When it comes to traffic control, we behave just like ants; next time you're stuck in a pedestrian jam, look out for alternating clusters of people navigating the rush hour.