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THE COORDINATED DANCE OF MIDGES

09-10-2017

Were you to observe a swarm of midges, it might seem that each one moves randomly around some point of reference such as a puddle or a lamp. However, appearances often deceive. Where there seems to be a great disorder, there may well be a strong correlation between the movements.

In a recent study published on Nature Physics, Professor Irene Giardina from the Sapienza Physics Department, in collaboration with the Collective Behaviour in Biological Systems (CoBBs) Group coordinated by Andrea Cavagna from the Complex Systems Institute (ISC-CNR), explains how experimental data collected from the analysis of midge trajectories narrates a completely different story, revealing the usefulness of a statistical physics approach to understanding collective phenomena in biology.

The researchers acquired stereoscopic sequences of the paths of individual midges and converted them into 3D trajectories to analyse the paths statistically. This procedure allowed the team to observe the spatial-temporal correlations between the movements. In other words, they quantitatively calculated the influence of an individual in a "group" on the behaviour of another individual in the same group, at given times and positions. The analysis revealed how the midges in different regions behaved in a coordinated way and how relations of mutual influence among the midges decayed over time. The decay times were present in every analysed swarm and swarms with larger coordinated regions had longer decay times.
Moreover, it was observed that, besides from this phenomenon, the spatial-temporal correlations of all swarms follow the same pattern. They obey "laws of scale,” a fundamental property for describing all swarms in a universal manner and modelling group behaviour.

“The study,” explains Irene Giardina, “is an important step forward in the application of statistical methods from Physics to biological systems, as well as providing solid experimental results that any future theory of swarms and collective movements on active matter will have to take into account."

CoBBS group is a joint group of the CNR Complex Systems Institute (UOS Sapienza) and the Physics Department. CoBBS studies 'flocking' and 'swarming' phenomena from experiments on real systems and developing data-based theories and models.