Sometimes in the animal world it is possible to witness behaviors that may appear, to the untrained eye, to be totally senseless. This is the case of the so-called “death spiral”that phenomenon in which the legionary ants find themselves in fairly common circumstances a going round and round non-stop when a single file closes in on itself and the “victims”, who have the instinct to follow each other, are deceived and are no longer able to get out of the circle. This condition is known and studied in detail and is called “death spiral”. Why does this happen and how to stop this effect?
What is the ant “death spiral”.
There death spiralin English ant mill or death spiral it is a behavioral phenomenon typical of some species ants legionaries due to their social organization. It refers to the formation of a spiral path, a circle around which the ants they walk incessantly. These insects, once they have entered the system, are unable to get out except in particular cases, which can lead to their death from exhaustion. The phenomenon of “dancing ants” was described in 1921 by the zoologist William Beebe and subsequently reproduced and confirmed by experiments conducted in the laboratory.
The species affected by this behavior are commonly called legionary ants and are characterized by very small or absent eyes, lack of a fixed anthill, large release of pheromones and one self-organized social structure. The species is an example of this Labidus praedator typical of Central-South America.
Individuals constantly traffic in search of food and to stay compact and move in unison, in the absence of developed vision, they use hormonal signals between conspecifics. They perceive the odorous signals of their companions and act accordingly, following the movement pattern dictated by the ant in front of them.
However, if the single file, for various possible reasons, it closes in on itselfthere is no longer a beginning or an end: in short, a vicious circlea continuously rotating circle where the ants follow each othertrapped by their own rules.
Why do ants chase each other?
Often everything starts from a small group of individuals that breaks away from the foraging nucleus thus losing the olfactory trace of the main group. A self-tracking mechanism dictated by the users is thus activated pheromoneschemicals that act as messages. The situation that is generated is: self-reinforcement: a loop is created, an organization without beginning or end, difficult to interrupt and which can lead most ants to perish from exhaustion. In doing so, these insects never stop chasing each other, they continue to walk undaunted until they die of starvation.
The zoologist William Beebeduring his studies, managed to observe and measure a death spiral of 370 m of circumference in which the ants took over two and a half hours to make a complete revolution.
This is from an ethological point of view behavior it seems to have gods useful implications to track the way home, find food and maintain the group, but it can be counterproductive. It seems to be the evolutionary price to pay for a collective foraging strategy, which is not always successful. This dysfunctional conduct we can see it as the other side of the coin of otherwise functional behavior. You might then ask: once the loop is formed for the ants is there no escape anymore?
How to block the infinite race
Break or change course it is possible if a hormonal change occurs in the signal, for example if one of the ants finds the original olfactory trace again. The dysfunctional signal can be covered with new smells even of external origin or interrupted by environmental or biotic factors of various nature (animals, weather, temperature, etc.)
In this case the group is forced to change the route due to an obstacle, but these actions do not necessarily always work. In highly organized species such as legionary ants the pursuit instinct of pheromones is very strong and difficult to ignore; it almost resembles a powerful spell that hypnotizes animals into eternal sleep.
