Damselflies use their vision to actively hunt prey and identify mates. The color is important for mate choice and intraspecific communication. Female Familiar Bluet damselflies, Enallagma civile, will change color from turquoise to brown during mating. What causes the color change?
The turquoise color is not a pigment but a structural color. The color is created by spherical granules packed into pigment cells just beneath the cuticle. The spheres contain structured arrays that reflect light relatively equally in all directions. Thus, the turquoise color is constant irrespective of viewing angle and not iridescent as in some structural colors.
Like the chameleon grasshopper, Kosciuscola tristis, the granules can be moved by microtubules. Movement of the granules away from the surface produces the brown color. It is interesting that two very different organisms evolved very similar color change mechanisms.