Stavenga and colleagues Jürgen Otto and Bodo Wilts used scanning electron microscopy and other techniques to study the spider's colors in depth. They discovered that the blue is not only a structural color, but that it's a type that's never been described before.
"The special photonic invention of the Maratus splendens scales is the insertion of two layers of extremely fine threads or filaments that subtly tune the refractive index profile of the multilayers, thus creating the distinct, blue color," Stavenga explained.
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The male peacock spiders use the patterns and colors on their bodies for visual communication, including wooing attentive females.
You can see them in action in this video, shot by Otto: