Treadmilling and dynamic protrusions in fire ant rafts

This is the data set for the manuscript relating to treadmilling and protrusion dynamics in fire ant rafts. The file titled, "README.pdf" contains detailed descriptions of its contents. Manuscript abstract: Fire ants (Solenopsis invicta) are exemplary for their formation of cohered, buoyant, and dynamic structures comprised entirely of their own bodies when exposed to flooded environments. Here we observe tether-like protrusions that emerge from aggregated fire ant rafts when docked to stationary, vertical rods. Ants rafts are comprised of a floating, structural network of interconnected ants on which a layer of freely active ants walks. We show here that sustained shape evolution is permitted by the competing mechanisms of perpetual raft contraction aided by transition of bulk structural ants to the free active layer, and outwards raft expansion due to deposition of free ants into the structural network at the edges, culminating in global treadmilling. Furthermore, we see that protrusions emerge due to asymmetries in the edge deposition rate of free ants. Employing both experimental characterization and a model for self-propelled particles in strong confinement, we interpret that these asymmetries likely occur stochastically due to wall accumulation effects and directional motion of active ants confined by the rafts’ boundaries. Together these effects may realize the cooperative, yet spontaneous formation of protrusions that fire ants sometimes utilize for functional exploration and to escape flooded environments.