Propagating Fronts in Columns of Fire Ants

For the past two decades, the study of active matter has revealed rich physics and universal behaviors, such as collective motion, across a wide variety of biological and synthetic systems with seemingly disparate particle interactions. Here we present our surprise observation and measurements of stable activity fronts propagating through 2 dimensional columns of thousands of fire ants. We then propose a model to explain the origin of these macroscopic non-linear fronts from simplified pairwise interactions between ants, and perform computer simulations that capture the experimental observations. Finally, we finish by comparing the fronts to other instances of collective motion observed in active systems.