Spaces between insects in laboratory swarms move like insects in natural swarms

Sparse swarms of flying insects show a high degree of spatial cohesion and are a form of collective animal behaviour; albeit one different from flocks and schools as they do not display ordered collective movements and under quiescent (laboratory) conditions long-range correlations are also absent. A better understanding of these outliers of collective behaviour may help to answer a long-standing open question in collective behaviour studies, namely ‘What is the signature that a group is ‘collective’? Even though dilute swarms of flying insects are mostly empty space no studies have reported on the dynamics of the spaces between swarming insects. Here I show that the spaces between insects (i.e., the centroids of empty tetrahedra formed by individuals and their 3 nearest neighbours) in laboratory swarms exhibit long range (maximal) correlations and novel dynamic scaling in common with insects in natural swarms. Spaces within laboratory swarms therefore move like insects in natural swarms. I thereby unify seemingly disparate behaviours as long range correlations between individuals are absent in laboratory swarms but present in natural swarms. With the aid of stochastic trajectory models of non-interacting insects I show that long range (maximal) correlations and the novel dynamic scaling arise generally and are not indicative of fine tuning. These results call for a re-evaluation of the importance of correlations and scaling in collective behaviours.