The nanostructures on the wings of Idea malabarica (Moore, 1877) were analysed using scanning electron microscopy, energy dispersive X‐ray spectroscopy, atomic force microscopy, Fourier transform‐infrared spectroscopy, and reflectance measurements. The chemical and morphological analyses revealed the chitin‐based intricate nanostructures. The influence of the nanostructures on the wetting characteristics of the wing was investigated using optical imaging. Applying the Maxwell‐Garnet approximation to the porosities within the nanostructures, the refractive indices, which relate the reflectance response, were estimated. It was concluded that the colour seen on the wings of the Idea malabarica originate from the nanostructural configurations of the chitin‐based structures and the embedded pigment.