This resulted in a patchwork of light-trails emerging over time (Figures \ref{294001} and \ref{535682}), reminiscent to the way ants and robot swarms lay trails to optimise foraging or area coverage \cite{Hunt2019}.
While analysing these experiments we observed that many of the moving Volvox slowed down when entering an illuminated path for a short period of time, before resuming their motion. It is known that Volvox are sensitive to light and that they reorient themselves in relation to a light signal with the goal of imrpoving photosynthesis \cite{Drescher2010}. Therefore, as a final demonstration of a building block of collective behaviours, we attempted to use this innate response as a means to selectively inhibit the movement of a subset of the population.