The ant death spiral, otherwise known as an ant mill, is a bizarre phenomenon wherein a group of army ants follow each other in a circle continuously until they somehow manage to break out or unfortunately, die of exhaustion.
The death spiral was first observed by scientist W.M Wheeler in his lab as he studied the ant species E. schmitti. He kept a colony of these ants inside a jar where they walked up and down in files repeated for hours.
When he removed the lid, the ants went out and made their way down to the circular base of the jar where they then started, as Wheeler put it, following each other like sheep and without the slightest inkling that they were traversing the same path. This went on for 46 hours until a few members broke out and caused the other ants to also spread out.
Wheeler considered this to be a limitation of instinct, where blind ants heavily reliant on their sense of smell and antennae kept following their trail without perceiving that they were making no progress and simply wasting their energy.
Why Do Ant Death Spirals Happen?
Ants are by no means dumb. In fact, they’re considered to be one of the most capable and smarter insects in the world. So how is it that they can fall into this death trap?
As Wheeler said, this is a limitation of instinct. Most ants, especially the visually impaired or blind ones rely heavily on pheromones and their sense of smell. For example, when army ants forage, the first ants in line leave scent trails which the rest of the group can detect and follow.
Then as they move, they further reinforce these trails to fully communicate to each other the direction that they are going and to ensure that the whole group can navigate to their destination.
When this system works, it allows ants to form large foraging parties and greatly increases the efficiency of food delivery.
However, the problem starts when some of these ants fail, usually by environmental triggers, to properly follow the main trail. These ants get lost and may somehow loop back to their own scent, all the while leading those behind them. When this happens, an ant death spiral is formed.
Can Ants Escape The Death Spiral?
It’s highly unlikely for ants to escape the death spiral, but it isn’t impossible. Much like how they start, environmental triggers such as strong winds or rain could possibly break the loop and cause the ants to scatter. Even then though, the possibility of escape remains low.
A study involving the species E. praedator shows how rain may sometimes fail to stop the death spiral. Even as rain disturbed the ants and made some of them hesitant in entering wet and exposed areas, they were forced to move onward due to the other ants pushing them from behind. So while the rain in this case did cause some shifts in the orientation of the spiral, the rotation ultimately continued.
As for escaping the spiral on their own, it’s almost impossible. The same study notes that while some of the ants were able to escape the spiral at one point, they eventually wandered towards the outer section of the spiral and got caught in it again. That said, the fact that they can sometimes break out does indicate that there is at least a chance of escape.
How Do Ants Communicate?
Ants mostly communicate by using chemicals called pheromones. These pheromones, which they can detect using their highly sensitive antennae, can be used to communicate different things such as the location of a food source or colony activity. It even allows them to distinguish colony mates from intruders, and identify dead ants.
Other than that, they can also communicate through sound and body language.
Why Do Ants Walk In A Line?
Ants walk in lines as they follow pheromone trails. As mentioned, when ants forage they follow the path set by those ahead of them to reach a food source. So when they do so, they naturally end up in a line as they detect and move along the path.
To recap, the ant death spiral is a strange and unfortunate bug in the usually effective pheromone system that ants follow. When such a system fails to work due to environmental triggers, ants start following each other in a never ending loop which, barring some sort interruption, tend to result in their eventual death due to exhaustion.