Figure 4.

(a) PDF of the swarm volume, separated by phase. Bright phases (dashed line) result in a more compact, compressed swarm. (b) Conditional acceleration of individual midges in the direction of the centre of mass as a measure of attraction strength and tightness of the swarm. Shaded areas indicate the standard error of the mean. During bright phases (dashed line), the swarm is noticeably more strongly attracted towards the centre of mass and thus more tightly bound to the centre than in the dark phases (solid line). (Online version in colour.)