I have a thing for butterflies – or more specifically for their erratic flight patterns and metallic shades. Even the cabbage white butterflies living in my backyard (and letting their young eat my cabbage), have this hint of iridescence giving the white of their wings a hint of shine. Sadly, my temperate climate doesn’t offer the full spectrum of butterfly bling that’s out there (but does save me from spiders with jaws strong enough to break my skin (mostly)).
A recent post I read about fear and spiders in Costa Rica, got me thinking about my own trip to the country years ago. Jungles are exotic – at least to me since I’ve always lived at mid-latitudes. They’re both fascinating and frightening, I certainly wouldn’t want to be out there alone at night. This trip was one of the few opportunities I’ve had to wander through jungles (and I didn’t get eaten!).
Out hiking, I spotted an iridescent green butterfly just off the trail. The green was colour of a granny smith apple and glittered with every flap the butterfly took. After getting my camera ready, I followed the insect through the undergrowth (mildly foolish, I know). I got lucky and it let me get close.
The iridescence in a butterfly’s wing (or dragonfly’s body, or a rooster’s tail, or even an oil slick on water), isn’t from a pigment. Instead an optical trick is required. In the butterflies case, the surface of the wing are covered in scales with a depth of one quarter the wavelength of blue (or green) light. Then the light reflected off the surface is augmented by the light reflected off the back surface giving the insect that fabulous iridescent effect.