Traffic jams are a perfect example of what happens when too many individuals circulate together in the same space. Movements in large ant colonies, however, seem to sidestep this problem. To solve the mystery of how ants manage traffic so wonderfully, researchers conducted 170 filmed experiments to observe ants commuting between their nest and a food source. Tests took into account the width of the path and the number of individuals included in the study (between 400 and 25,600) in order to vary the density – the number of insects per unit of surface.

What they saw surprised them: when density increases, ant flows swell and then become constant, whereas human traffic, above a certain density threshold, slows to zero flow and causes a jam . Ants, on the other hand, accelerate until a maximum flow or capacity on the path is reached. When traffic becomes too dense and causes too many collisions between ants, they change tactics, preferring to avoid time-consuming collisions instead of continuing to accelerate. Similarly, researchers noted that at excessively high density levels, ants refrain from joining the flow of traffic and wait for it to thin out instead.

While ant traffic is comparable to pedestrian and vehicle flows in many ways, it is also fundamentally different. Ants, protected by their exoskeleton, are not afraid of collisions and can accelerate where we humans prefer to slow down. In addition, movements in ant colonies share a common goal: foraging, which is carried out effectively regardless of density. Ants seem to avoid the traffic jam trap by continuously adapting their traffic rules to suit local crowding, whereas car traffic follows invariable rules such as stopping at a red light regardless of traffic.

Ants running on a bridge. © Emmanuel PERRIN/CRCA/CNRS Photothèque