Movie S2

The water surface of a petri dish was used as a treadmill for Acromyrmex lundii worker ants. A single vertical black strip was provided as a visual cue which was slowly moved around the petri dish. The angular position of the ant and stripe are shown in the right-hand graph. The ant exhibited directed movement towards the strip which indicates that visual cues are recognised by this species. Visual cues are probably an important fallback option when chemical cues are absent.