Physics (Internal)

Statistical Physics of Collective Load Transport by Ants

This event is part of the Biophysics/Condensed Matter Seminar Series.

Collectively carrying a heavy load is a hard task and in fact is rarely seen outside ants and humans. Conflicts within the group must be suppressed to succeed with efficient collective transport. However, conformism may render the system unresponsive to new information. Collective transport by ants is therefore an ideal model system to study how animal groups optimize their opposing requirements. We combine experiments and theory to characterize the collective transport. The ants are modeled as binary Ising spins, representing the two roles ants can perform during transport. It turns out that the ants poise themselves collectively near a critical point where the response to a newly attached ant is maximized. We identify the size as being proportional to an inverse effective temperature and thus the system can exhibit a mesoscopic transition between order and disorder by manipulating the size. Constraining the cargo with a string makes the system behave as a strongly non-linear pendulum. Theoretically we predict that a Hopf bifurcation occurs at a critical size followed by a global bifurcation where full swings emerge. Remarkably, these theoretical predictions were verified experimentally.