Propagating Activity Fronts in Columns fo Fire Ants

For the past three 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 two-dimensional columns of thousands of fire ants. We then propose both computational and analytical models to explain the origin of these macroscopic non-linear fronts from simplified pairwise interactions between ants. Finally, we finish by comparing these fronts to other instances of collective motion observed in active systems.