Collective behavior of inanimate boats

We propose an inanimate system composed of camphor boats in an annular water channel in order to understand the collective motions. The boats move on the water surface spontaneously and interact with one another through the concentration of the camphor molecules on the water. We observed several modes of collective motion, e. g., behaviors analogous to traffic flow or an ant trail. Our system provides a convenient experimental setup for the investigation of a variety of collective motions.