The Death Spiral Information Cascade
The self-organization of army ant colonies produces particularly unique behaviors in army ants– the most bizarre and notable being the ant mill, or more colloquially, the “death spiral”. Unlike most other ant species, army ants are blind and lack permanent nesting sites. This means that army ant colonies are constantly on the march for food, communicating their movement patterns through pheromone trails. Each traveling ant leaves behind a pheromone trail that other ants may follow. When successful, this system allows foraging parties to lead larger groups back to food, but when unsuccessful, produces a deadly phenomenon– the ant mill.
When a group of ants are separated from the main foraging party, they may lose the pheromone track and begin to follow one another. The group will form a continuously rotating circle that often remains unbroken until the participating ants die of exhaustion.
We can look at this behavior as a generalization of the information cascade system in Chapter 16 where each ant does not have private information to guide its decision but must instead rely on the signal of an ant who has acted previously. This signal is the pheromone trail left by an ant, and the decision to be made by any ant receiving this signal is whether or not to follow the trail. Because the behavior of army ants depends on the “governance” of self-organization as aforementioned, it is most likely that any ant will choose to follow the signal of a previous ant. Therefore, we have an information cascade where each ant will always make the decision to follow the previous ant’s signal.
Main source: Why Do Army Ants Commit Suicide? (treehugger.com)