Ants use the panoramic skyline as a visual cue during navigation

Foragers of many ant species learn long, visually guided routes between their nest and profitable feeding grounds [1-3]. The sensorimotor mechanisms underpinning the use of visual landmarks are much studied [3], but much less is known about how ants extract reliable visual landmark information from a complex visual scene. For navigation, useful visual information should be reliably identifiable across multiple journeys in differing lighting conditions, and one such robust source of information is provided by the skyline profile generated where terrestrial objects contrast against the sky. Experiments with ants and bees [4-6] suggest that insects might use directional information derived from the skyline, and in the work reported here, we explicitly tested this hypothesis. Ants were trained to shuttle between their nest and a feeder. We then recreated the skyline profile as seen from the feeder using an artificial arena with variable-height walls. Ants returning from the feeder were captured near their nest entrance and released in the arena. Ants followed the direction given by the artificial skyline when it was aligned with their habitual homeward compass direction or rotated by 150°. This result indicates that a crude facsimilie of a skyline can functionally mimic the natural panoramic scene.