"At least 40 species of tarantulas come in shades of blue. [...] To find out more about the "tarantula blue," researchers used different microscopy techniques to analyze tarantula hairs. They found that although these species share a shade of blue, tarantulas don't use pigments to produce it. Instead, the blue colors are produced thanks to nanostructures in the spiders' hair, which reflect blue light. And these nanostructures differ between species, the scientists found. Most importantly, however, these blue colors don’t change intensity or hue as the viewing angle changes. That's a big differentiator from the highly iridescent structural colors seen in most birds, butterflies, and beetles."