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

TL;DR

This study models cooperative ant transport as a self-propelled particle system, linking microscopic ant behavior to macroscopic load movement through Langevin equations, revealing phase transition phenomena.

Contribution

It introduces a macroscopic self-propelled particle model for ant cooperative transport, connecting microscopic rules to emergent load dynamics and phase transition behavior.

Findings

Load movement well described by Langevin equations

Autocorrelation time of velocity direction increases with group size

Maximum autocorrelation time of speed at intermediate group size

Abstract

Paratrechina longicornis ants are known for their ability to cooperatively transport large food items. Previous studies have focused on the behavioral rules of individual ants and explained the efficient coordination using the coupled-carrier model. In contrast to this microscopic description, we instead treat the transported object as a single self-propelled particle characterized by its velocity magnitude and angle. We experimentally observe P. longicornis ants cooperatively transporting loads of varying radii. By analyzing the statistical features of the load's movement, we show that its salient properties are well captured by a set of Langevin equations describing a self-propelled particle. We relate the parameters of our macroscopic model to microscopic properties of the system. 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. This corresponds to the critical slowdown close to the phase transition identified in the coupled-carrier model. Our findings illustrate that a self-propelled particle model can effectively characterize a system of interacting individuals.