Speed-dependent attraction governs what goes on at the heart of midge swarms (Vol. 48, No. 3)

Trajectories of individual midges within a swarm recorded using high-speed cameras

New study reveals swarm cohesion stems from an adaptive behaviour, where the faster individual midges fly, the stronger the gravitational-like force they experience.

Ever wondered what makes the collective behaviour in insect swarms possible? The authors modelled the effect of the attraction force, which resembles Newton’s gravity force, acting towards the centre of a midge swarm to give cohesion to their group movement. In a recently published work, their model reveals that the gravity-like attraction towards the heart of the swarm increases with an individual’s flight speed. The authors confirmed the existence of such an attractive force with experimental data. They chose to focus on insect swarms, rather than bird flocks or fish shoals, because interactions between neighbouring individuals appear not to play a key role. This makes insect swarms easier to model. Instead of building a model describing the microscale movement of individuals and confronting it with experimental data, the authors built a model of swarm behaviour that is consistent with experimental observations, in terms of swarm density, of individual midges’ speed and acceleration.

A. M. Reynolds, M. Sinhuber and N. T. Ouellette, Are midge swarms bound together by an effective velocity-dependent gravity?, Eur. Phys. J. E 40, 46 (2017)