A jet breaks into droplets that elongate into ellipses...in turn unstable to buckling, as soon as they are thin enough for one wavelength to develop. We end up with these structures that can also be understood through symmetry arguments - see this beautiful work: journals.aps.org/prl/abstract...

When C.reinhardtii cells swim one behind each other, they tend to pull on their neighbors, leading to a pearling instability. In contrast, when they swim side to side, they push on their neighbors, leading to a buckling instability. We control both by steering these phototactic cells with light.

Happy to share that our work on active phase separation by photophobic microalgae is now published in PRL!
journals.aps.org/prl/abstract...

When surrounded by multiple light sources, cells hide behind each other, leading to the quick formation of a macroscopic branching pattern.