M. Betterton

Active matter with intent: clog control in excavating collectives

Ensembles of self-propelled systems can spontaneously form clusters, clogs and jams. However, in crowded biological and robotic swarms, clog mitigation is important for collective task completion. To discover principles by which active materials can ensure high task performance under severe constraints, we studied workforce organization in fire ant tunnel excavation, examining the biological strategies in theoretical, computational and robophysical models. Workload inequality coupled with selective retreats led to high performance excavation, despite the lack of centralized guidance. Tools from the study of dense particulate ensembles elucidated how the seemingly counterintuitive strategies of idleness and retreating lead to optimum traffic conditions: idleness reduces the frequency of flow-stopping clogs, and selective retreating reduces clog dissolution time for the rare clogs that still occur. Our results point to strategies by which active materials can become task-capable without sophisticated sensing, planning and global control of the collective.