Close-up of a dragonfly wing, not stained glass.
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Fun fact: common buckeye butterflies (Junonia coenia) can be selectively bred to be blue fairly easily!
It turns out the only thing needed to go from brown to blue is a slightly thicker lamina, which is a flat layer at the bottom of the wing scale:
The lamina's iridescence is caused by the same phenomena as soap bubbles: thin-film interference. When light hits the transparent film of the lamina, it reflects off both the top and bottom of the layer.
Depending on the thickness and refractive properties of the material, the two reflected light waves can be in sync (image below) or cancel each other out. At the perfect thickness, the blue waves of light are enhanced and the butterfly becomes iridescent!
Because the difference in thickness needed to cause iridescence is so slight, it took less than a year to shift a population from just a few blue scales to full-on fabulous blue.
Photos & figures by Rachel Thayer, Nipam Patel, and Edith Smith.
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~ Texture | Pattern | Design ~
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