Community living offers great benefits. One drawback is overcrowding, which leads to unneighborly behavior. Confusing friend with food, predators appear within the playfully swimming bacterial cooperatives.
The "Vampire-berry" (Vampirococcus) attaches to and eats away the larger prey cells. Other microcosmic predators like Bdellovibrio slip just inside the surface of an unsuspecting neighbor, close the membrane and start digesting. A common predator lives and feeds by itself until resources diminish. When nearly overcome by crowding, it moves inside its intended victim and starts to divide.
It is speculated, in one of nature's luscious ironies, that the outcome of invasion, followed by truce, produces a grand blossoming in the history of life.