Social interactions lead to motility-induced phase separation in fire ants

Some active matter systems as they evolve, can be characterized by spatially varying density, with some regions that are dense and immobile, and other regions with lower density that accommodate most mobile particles. The authors show that this phenomenon can also be observed as an effect of the social interactions between fire ants. Collections of fire ants are a form of active matter, as the ants use their internal metabolism to self-propel. In the absence of aligning interactions, theory and simulations predict that active matter with spatially dependent motility can undergo motility-induced phase separation. However, so far in experiments, the motility effects that drive this process have come from either crowding or an external parameter. Though fire ants are social insects that communicate and cooperate in nontrivial ways, we show that the effect of their interactions can also be understood within the framework of motility-induced phase separation. In this context, the slowing down of ants when they approach each other results in an effective attraction that can lead to space-filling clusters and an eventual formation of dynamical heterogeneities. These results illustrate that motility-induced phase separation can provide a unifying framework to rationalize the behavior of a wide variety of active matter systems.

Automated summary

This study shows that the social interactions between fire ants can result in spatially varying density, due to the slowing down of ants when they approach each other. This phenomenon can be understood within the framework of motility-induced phase separation, providing a unifying framework for understanding the behavior of a wide variety of active matter systems.