Cool Butterfly Photonic Crystals The small structures in the
scanning electron microscope image of a butterfly wing scale (a)
are natural photonic crystals that give the wings of some
butterflies their brilliant iridescent blue colors. The
structures in the second image (b) are responsible for a blue-
violet iridescence. In the third image (c), the small structures
are almost entirely absent, and the butterfly wing scales are a
dull brown shade. New research suggests that photonic crystals
keep butterfly wings cooler, as well as making them beautiful.
In higher elevations where butterflies are more reliant on
sunlight to keep them warm, some of the insects have evolved
wing scales in which the photonic crystals have been disrupted
(as in image c), improving the chances that they survive long
enough to mate despite the frigid climate.