Abstract

If I asked you to give me an instance of collective motion in the natural world, namely the phenomenon of the spontaneous emergence of ordered movement in a large group of organisms, your response would fall into one of two categories. Either, your example would exhibit a clear unidirectionality in the velocity of the organisms (eg migratory bird flocks, schooling of fish or collective cell migration) or it does not (Swirling behaviour eg bacteria or the formation of circular milling structures eg fish shoals). I will present a model organism, the plant-animal worm Symsagittifera roscoffensis, that exhibits a myriad of collective behaviour from both categories. I will focus on three particular collective behaviours exhibited by the worms, utilising a combination of theory, numerical simulations and experiments (both in the lab and in the field in Guernsey) in order to address both how do these structures emerge but also why, demonstrating that collective motion is an integral part of all aspects of daily life for the worms.