What’s in a band? The function of the colour and banding pattern of the Banded Swallowtail

Butterflies have evolved a diversity of colour patterns, but the ecological functions for most of these patterns are still poorly understood. The Banded Swallowtail butterfly, Papilio demolion demolion, is a mostly black butterfly with a greenish-blue band that traverses the wings. The function of this wing pattern remains unknown. Here, we examined the morphology of black and green-blue coloured scales, and how the colour and banding pattern affects predation risk in the wild. The protective benefits of the transversal band and of its green-blue colour were tested via the use of paper model replicas of the Banded Swallowtail with variations in band shape and band colour in a full factorial design. A variant model where the continuous transversal green-blue band was shifted and made discontinuous tested the protective benefit of the transversal band, while greyscale variants of the wildtype and distorted band models assessed the protective benefit of the green-blue colour. Paper models ...