Colour vision of the foraging swallowtail butterfly Papilio xuthus

This paper demonstrates that foraging summer-form females of the Japanese y ellow swallowtail butterfly Papilio xuthus have colour vision. The butterfl ies were trained to feed on sucrose solution placed on a disk of a particul ar colour in a cage set in the laboratory. After a few such training runs, a butterfly was presented with the training colour randomly positioned with in an array of disks of other colours, but with no sucrose solution. The re sults indicate that the butterflies learn rapidly to select the training co lour reliably among different colours. The training colour was also correct ly selected when it was covered with neutral density filters to reduce its brightness, or even when the colour was presented together with disks of a variety of shades of grey. These results demonstrate convincingly, for the first time, that a butterfly has true colour vision.