Bees can combine range and visual angle to estimate absolute size

Previous work has shown that bees can discriminate objects viewed on a vertical plane on the basis of angular size, as well as objects on a horizontal plane on the basis of range. In the present study, we first demonstrate the bees’ ability to measure range to a vertical surface, and discriminate angular subtense to objects on a horizontal plane. The question whether they can combine the independent measurements of angular size and range to infer the absolute size of an object is then examined for the horizontal and vertical planes. Bees were trained to expect a reward of sugar solution when they correctly discriminate a black circular target of fixed absolute size from a similar target which is of different absolute size. Apart from absolute size, the two targets may differ from each other in either angular size, or range, or both, depending on the experiment. In the experiments conducted on a vertical plane, the two targets were each placed in one arm of an Y-shaped choice box. In the experiments on the horizontal plane the bees could freely fly above the targets. In both types of experiments, using a variety of test situations, the bees discriminate the target of a given absolute size irrespective of angular size or range.