How butterflies become blue

There are no natural blue pigments in biological tissues, so animals resort to optical tricks to produce luxurious blue tones. A study in the Journal of Experimental Biology reveals how brilliant South American morpho butterflies (Morpho peleides) use thinly spaced chitin plates and ridged structures that select out blue wavelengths to produce their lustrous wing colours.

The image here is a coloured scanning electron micrograph of a scale from the wing of a blue morpho butterfly. Layers of wing scales are transparent but tiny ridges on the scales break up and reflect light to give the scales their shimmering iridescent appearance.

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