Max Delbruck Prize in Biological Physics (2021): From individual motion to group behavior: what regulates collective dynamics in natural swarms of insects

Experiments on swarms of insects show that these groups obey robust statistical laws, thereby supporting a physics-based approach. I will discuss how, when modeling these systems starting from the data, three crucial ingredients must be incorporated in their theoretical description: activity, behavioral inertia, and mutual alignment. I will first consider small sparse groups, where interactions play no role, and show how to extract from experimental data information on the order of the dynamics, on inertial terms and on the active potential regulating the speed of individuals. Then, I will consider larger and denser groups, where interactions are strong and correlations are long-range. In these groups dynamical correlation functions exhibit dynamic scaling, with a non-trivial dynamic critical exponent. Both the value of the exponent and the shape of correlations indicate that behavioural inertia is needed to explain the large scale behavior in the critical regime.
The whole analysis suggests that the appropriate theoretical description for these systems is a ferromagnetic field theory that includes both reversible and dissipative terms, defining a novel dynamical universality class of biological active matter.