Some insects have photonic nanostructures on parts of their body that can, for example, produce structural colours or achieve transparency for camouflage. One such insect is the glasswing butterfly Greta oto, which has wings that are mostly transparent, with low reflectance of a few per cent across the visible spectrum and for viewing angles up to 80°. The regular arrangement and size of nanostructures on the surfaces of certain insect's eyes or wings is responsible for their antireflection properties. Hendrik Hölscher and colleagues at the Karlsruhe Institute of Technology have now revealed that the origin of the transparency of the wings of Greta oto is instead linked to the irregular properties of nanopillars found on the wing surface.
The researchers found that the nanopillars are irregularly arranged with an average spacing of 120 nm and have random heights in the range of 400–600 nm. They proved that randomness in the arrangement and size of the nanopillars is the cause of the omnidirectional antireflection properties of this butterfly's wings by simulating the optical properties with an analytical model that includes a Gaussian distribution of the nanopillars' height.
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De Ranieri, E. Biological nanostructures: Transparent randomness. Nature Nanotech (2015). https://doi.org/10.1038/nnano.2015.122
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DOI: https://doi.org/10.1038/nnano.2015.122