Nest-Level Phase Transition Drives Synchronized Activity Bursts in Ant Colonies

Many natural complex systems exhibit synchronization, characterized by temporal coherence among the dynamics of their units. In ant colonies, synchronization manifests through activity bursts: sudden, sharp spikes of motion by a significant portion of workers throughout the nest, followed by durations of quiescence. These activity bursts were discovered three decades ago and studied since then; yet, the mechanisms that lead to their emergence remain elusive. Here, we present a model of ant activity that integrates both the motion of individuals within the nest and the transitions between behavioral states. By balancing microscopic behaviors in the model, we identify a nest-level phase transition from unsynchronized to synchronized activity and draw several connections between model predictions and empirical observations in the literature. Our analysis begets two key insights: (i) activity bursts emerge as a balance between the responsiveness of the colony to the first ant that activates and the ability of the colony to completely deactivate before the onset of the next burst, and (ii) the timescale of the motion of individuals through the nest is faster than that of the burst, suggesting that ants operate in a high-speed interaction regime where new behaviors are near-instantaneously transferred through the nest. We relate these findings to the broader literature on synchronization in complex systems, highlighting the need for periods of quiescence followed by the rapid communication of a new behavior through a population of connected units.