Large systems of self-propelling particles (SPP) form a special class of so-called active matter. Examples of such systems found in nature are: flocks of birds, schools of fishes, ants, groups of bacteria, etc.
One can often see how these animals develop coherent motion, amazing the observer by the diversity of its forms and shapes.
Emergence of collective behaviour in active matter from relatively simple motion of single organisms is on the forefront of modern interdisciplinary research.
A review of a previous talk by Andrei