Polarization-dependent Tessellated Pattern of the Wing Scale of the Parides Sesostris Butterfly

The Emerald-patched Cattleheart butterfly Parides sesostris is known to possess a gyroid-type photonic crystal within its wing scales. However, the photonic crystal is observed to be separated into many small domains with different crystal orientations. It has been assumed that this domain structure causes the beautiful tessellated pattern of the scale that can be observed under a crossed polarizer and analyzer. To confirm this assumption, we carefully observed the polarization-dependent reflection from the wing scale, examined the surface morphology of photonic crystal domains using electron microscopy, and theoretically calculated the reflectance of a gyroid-type photonic crystal. By comparing the results of these investigations, we show that the tessellated pattern originates from different angle between the incident polarization and the crystal orientations of different crystal domains.