The social organization of ants can reach extreme paradoxes, even to mass suicide in order to follow the leader. This is a very particular phenomenon called “death spiral” in which thousands of legionary ants, following each other, begin to circle relentlessly, forming a spiral which, when closed, leads to their death.
Why it happens
Known as ant mill or death spiralis part of the typical behavior of some ant species and their social organization. The phenomenon was first described in 1921 by the zoologist William Beebe and subsequently reproduced and confirmed by experiments conducted in the laboratory. The particular species of these Hymenoptera is ccommonly called legionary ant and is characterized by very small or even absent eyes, the lack of a fixed anthill, a large release of pheromones as well as a self-organized social structure.
Insects constantly looking for food, given the absence of developed vision, tend to move in unison using pheromones, i.e. the odors released by the other ants that precede themthus forming a very long chain. When for various reasons some ants lose the main trail, perhaps attracted by a food source, the others follow it forming an increasingly larger concentric spiral in continuous rotation that traps them until they die.
Because they start going in circles
Usually, as mentioned, everything starts from a small group of ants that detaches itself from the central nucleus, thus losing the main olfactory trace. No longer being able to understand the path they activate a self-tracking mechanism of their pheromones which leads the group to start going around in circles in an increasingly larger spiral which then leads them to die from exhaustion, because they do not stop following each other in any way. The zoologist William Beebe, during his studies, managed to observe and measure a death spiral 370 m in circumference in which the ants took over two and a half hours to complete a complete revolution.
It was he who explained this behavior from an ethological point of view is necessary to track the way home, find food and be more protected by the groupalthough, precisely these factors can lead to a sort of mass suicide. This seems to be the price you pay for sustenance and the evolution of the species itself.
The possibility of “exiting the spiral”
Although it is very rare, there is, however, the possibility for ants to escape from this deadly spiral if a hormonal change occurs in the signal, for example if one of the ants finds the original olfactory trace.
Or the dysfunctional self-tracking signal may be blocked by external factors such as the presence of animals, temperature or weather. In these cases the group changes the route due to an obstacle, thus breaking the chain, but, as mentioned, this really happens in very rare cases.