Connecting cooperative transport by ants with the physics of self-propelled particles

Abstract

Some ant species are known as efficient transporters that can cooperatively carry food items which would be too large for a single ant. Previous studies of cooperative transport focused on the role of individual ants and their behavioral rules that allow for efficient coordination. However, the resulting detailed microscopic description requires a numerical treatment in order to extract macroscopic features of the object's trajectory. Here, we instead treat the carried object as a single active swimmer whose movement is characterized by two variables: velocity amplitude and direction. We experimentally observe Paratrechina longicornis ants cooperatively transporting loads of varying sizes. By analyzing the statistical features of the load's movement, we show how the salient properties of the cooperative transport are encoded in its deterministic and random accelerations. We find that while the autocorrelation time of the velocity direction increases with group size, the autocorrelation time of the speed has a maximum at an intermediate group size, corresponding to the critical slow down close to the previously identified phase transition. Our statistical model for cooperative ant transport demonstrates that an active swimmer model can be employed to describe a system of interacting individuals.