An ant mill is a strange and rather bizarre phenomenon that is also known as a death spiral. This vortex of death involves a group of ants continuously following the ant in front of them, forming an endless loop. Army ants are the only species with this deadly behavior, and the ants will eventually die of exhaustion. The explanation is still limited, but we do have some answers to this.
1What Causes An Ant Mill?
Army ants are different from most other ant species; they are blind and lack permanent nesting sites. That means the army ant colonies are constantly on the march for food. They communicate their movement patterns through pheromone tracks. Each traveling ant leaves behind a pheromone trail that other ants can and may follow. Sometimes, through terrain, wind, or just bad luck, the lead ant circles back and crosses the trail of the last ant. People can also sometimes accidentally cause an ant mill to form if they disturb an ant trail. This causes separation of a large group, and the loop begins.
When a group of army ants is separated from the main foraging party, they lose the pheromone track. When that happens, they begin to follow one another, creating a circle known as the death spiral. Their instinct is to follow the pheromone track, and each ant follows the ant in front of it. So when the ant in the front loses its track and forms the spiral, there is no end to the circle. Eventually, the ants will die of exhaustion and starvation.
2When Did It Happen?
The first time this bizarre phenomenon was recorded was in 1921, by William Beebe, explorer and naturalist. He stood there in the Guyana jungle, witnessing something that he couldn’t take his eyes off of. Then, he timed the spiral. The circle was 1,200 feet (366 meters) in circumference, and each ant completed one lap every 2.5 hours. They continued their once-purposeful journey for 46 consecutive hours before meeting their demise. He called it a “death mill”, and we call it an “ant mill” today.
3Can Ants Escape The Death Spiral?
Not by themselves, no; every ant mill ends in the death of all the army ants. They will blindly follow the scent of the ant in front of them until they die. However, if luck is on their side, they can live to forage another day. Weather events like rain or wind can disrupt the scent trail and scatter the trapped ants. Sometimes, there are a few individual ants that manage to break away from the outer edges. And some other times, they find the center exit and create a new trail that breaks the loop. If you come across a death spiral and want to help them, you can. You can blow them or slide a thin object into the circle to scatter the ants. This will break the circle, and no ants will die.
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