Movie S1

The water surface of a petri dish was used as a treadmill for Acromyrmex lundii worker ants. The surface tension supported medium-sized workers but the slippery surface together with the concave meniscus prevented the ants from reaching the wall of the vessel (first and second graphs showing the video image and the XY-position of the tracked position in the petri dish). In the absence of any visual cues, ants showed an innate bias to turn counter-clockwise (angular position of ant, third graph from left). By adding the slipped steps of the front limbs to the ant's position, the effectively walked path was reconstructed which revealed a looping pattern (right-most graph).