Motion cues provide the bee's visual world with a third dimension

Abstract

To extract the third dimension from a two-dimensional retinal image most insects, including bees, cannot rely on mechanisms common in vertebrates such as accommodation, binocular convergence or stereoscopic vision^1,2. Instead, they use the apparent size of familiar objects (the nearer the object, the larger its image), and objects' apparent motion (the nearer an object, the higher the speed of its image) ^3–8. In several studies^9–12 bees have been found to exploit size cues, whereas in others^6,11,13 they seem to use both strategies. We have studied the influence of motion cues in isolation by excluding size cues. We report that bees can discriminate between objects at different distances irrespective of their size. This discrimination is mediated primarily by the green-sensitive visual channel and is therefore colour blind, like all of the motion-dependent behaviours investigated so far in the bee^14–17. The bee's ability to discriminate range by motion of the image explains how bees manage to manoeuvre in novel environments, where the size of objects is unknown.