In a video clip recently uploaded by a netizen, a flock of ants form a spiral and run clockwise in it continuously until they die of exhaustion. In the circle is a pile of dead body of ants. No one seems to dare to stop.

This phenomenon, known as "Ant Death Spiral", perhaps exists for thousands of years. It was first observed in 1936 when an American animal psychologist Theodore Schneirla met with several hundred ants running in a circle.

The phenomenon lasted for a whole day. And it was not even stopped by a heavy rain. On the following day, the death carousel left many dead behind as it continued to spin until some groups of ants broke it and split away from the group.

A well-known insect photographer Alex Wild described the phenomena several years ago on his blog. "I used to see ant spirals all the time when I lived in Paraguay, and not just in the field..." He found circles of ants whirling about on top of plates in the kitchen, or sometimes an intimate ring of 5-6 ants on a coffee mug.

Expert said that these circular mills are a common byproduct of army ant navigation. On the earth there are over 200 kinds of army ants, but genetic evidence suggests that they may have a common ancestor which is completely blind, so ants in this genus get about by following the insect in front and laying down a chemical trail.

The system works well enough in a straight line. The trouble begins when the ants loop around and intersect their own path.