This whole spectacle at the front steps of my apartment remains very unexplained to me
A strange phenomenon: army ants navigate by following the pheromone trail left by fellow ants, always favoring more traveled paths that might lead to a food source or back to the colony. The simplistic laws that govern the behavior of ants are so reliable that computer programs can simulate entire ant colonies in a fairly reliable way.
What you’re seeing here is a total glitch. These ants are following each others sent in what has developed into a “circular mill” or a circle of death. Without intervention they will continue to march this way, never reaching the hive, until they die one by one of exhaustion. The process takes about 3 days.