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

Abstract

Abstract 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.