3. Glasswinged Butterfly
As the name indicate the butterfly has transparent wings. It is also called as greta oto and found across Mexico and Colombia. Their transparent wings make it too difficult for predators like birds and reptiles to catch them. In fact the reddish brown border on it’s wings itself make them visible but not so easy. Great oto butterflies also exhibit long distance migration to Florida. They mainly feed on common flower called lantana.
The wings are transparent, with a span of 5.6 to 6.1 cm. The butterfly’s most common English name is glasswinged butterfly and its Spanish name is mariposa de cristal, which means «crystal butterfly». The tissue between the veins of its wings looks like glass, as it lacks the colored scales found in other butterflies. The opaque borders of its wings are dark brown, sometimes tinted with red or orange, and its body is dark in color.
The transparency of its wings results from the combination of three properties: first, from the low absorption of the visible light by the material constituting its wings, second, from the low scattering of the light passing through the wings and finally, from the low reflection of the light impinging on the wings surface.
The latter occurs for a broad range of incident wavelengths, covering the whole visible spectrum, and of incidence angles. This broadband and omnidirectional anti-reflection property originates from nanopillars standing on the wing’s surface which ensures a gradient of refractive index between the incident medium and the wing’s membrane. Those nanopillars, non-periodically arranged on the wing’s surface, possess a high aspect ratio in excess of 6, where the radii are below the wavelengths of the visible light. Besides, they feature a random height and width distribution, which is directly responsible for the smooth refractive index gradient and thereby for the broadband and omnidirectional anti-reflection properties. These properties are further improved by the presence of pedestals at the base of the nanopillars.