The green colour is created not by the refraction of light, but is due to the presence of a pigment. | Image: Alamy Stock

The green stripe across its wings protects this Asian swallowtail butterfly (Papilio demolion demolion) from predators. This has been shown in an experiment with differently patterned paper butterflies. Models were provided with such a stripe and placed in the forest: they were found to be practically invisible to birds. An analysis by Bodo Wilts from the University of Fribourg has proven that this colour is made by pigmentary absorption, not by iridescent structural colours as is the case in other insects. This makes the stripe green from any angle, and provides optimum camouflage.

E. J. Tan et al.: What’s in a band? The function of the color and banding pattern of the Banded Swallowtail. Ecology and Evolution (2020)