Congestion and communication in confined ant traffic

Many social animals move and communicate within confined spaces. In subterranean fire ants {\em Solenopsis invicta}, mobility within crowded nest tunnels is important for resource and information transport. Within confined tunnels, communication and traffic flow are at odds: trafficking ants communicate through tactile interactions while stopped, yet ants that stop to communicate impose physical obstacles on the traffic. We monitor the bi-directional flow of fire ant workers in laboratory tunnels of varied diameter $D$. The persistence time of communicating ant aggregations, $\tau$, increases approximately linearly with the number of participating ants, $n$. The sensitivity of traffic flow increases as $D$ decreases and diverges at a minimum diameter, $D_c$. A cellular automata model incorporating minimal traffic features---excluded volume and communication duration---reproduces features of the experiment. From the model we identify a competition between information transfer and the need to maintain jam-free traffic flow. We show that by balancing information transfer and traffic flow demands, an optimum group strategy exists which maximizes information throughput.