The way it works with my microscope studies is that I rarely see organisms one a time. They are always in bunches. I will always see them in groups except for those which swim quickly around. The question is how much of microbes being close together is really social or group behavior? How much does their motion depend on each other and how much of it is just being in a limited space? Many times these organisms seem to bunch--even touching each other. I have come to see this as some kind of social behavior.
https://youtu.be/2D3iFIqfts4