It is possible that you have ever come across one of those videos in which a group of ants appears circling, as if they had suffered some catastrophic error in their system and had been stuck repeating the same action.
As it turns out, these ants have not gone crazy. They only obey their impulses. This phenomenon is exclusive to the 200 species of legionary ants (those from the movie “Marabunta” that terrified more than one of us in our childhood) present in Africa and South America. A very curious characteristic of these ants is their nomadic lifestyle: instead of building ant hills, they move in unison in large groups during the day and build makeshift nests at night.
But the most impressive feature of this class of ants is their hunting strategy, which consists of moving in gigantic groups of between 100,000 and 2,000,000 individuals, forming columns between 20 and 200 meters wide, and attacking any prey en masse. that they find in their wake (that is, the film was not so far from reality). An ancestor of today’s legionary ants is believed to have developed this strategy around 105 million years ago in southern Gondwana , the continent that would become Africa and South America, the separation of which allowed the species to diversify on both sides of the new ocean. , preserving this peculiar characteristic.
But, although it is very successful, this strategy has a flaw. Legionnaire ants are blind, so they maintain cohesion in their groups by following the pheromone trails left by their companions in their wake.
This communication system is very useful to maintain their large groups, but it is lethal if an ant gets lost: when a small group of ants loses the pheromone trail and separates from the main group, then its members can begin to follow their path. own trail … And they end up following each other, going around in circles without stopping, until they die of exhaustion.
Although, to tell the truth, the clueless group does not have to be so small. The largest ant spiral ever observed was described in 1921 and had a 400-meter circumference that ants took two and a half hours to complete.
