Natural Iridescence

Source: Eddy Van 3000. License: CC share-alike, attribute

Just look for a bit. I'll be quiet.

I came across the morpho butterfly in a book awhile back, but forgot the name. To my delight, I saw this picture today on Flickr while hunting for something else, and finally got to see a much bigger picture than the one in the book.

That blue is not merely "intense". Tiny scales on the wing actually bounce the lightwaves around to heighten the color. As the current Wikipedia article explains:

These colors are not a result of pigmentation but are an example of iridescence: the extremely fine lamellated scales covering the Morpho's wings reflect incident light repeatedly at successive layers, leading to interference effects that depend on both wavelength and angle of incidence/observance.

There's a diagram that might make that a bit clearer. Basically, when light hits you or me, what doesn't get absorbed simply bounces off our skin and goes its merry way. But when lights hits these scales, it cascades into multiple layers of reflections. Some waves bounce off the highest scales, some off the lowest, and some off those in between. Almost all of these reflected waves cancel each other out. But the scales are perfectly spaced so that these particular shades of blue bounce back in phase--and we see a brilliance that, unless I'm mistaken, isn't possible with normal pigments.

To top all this off, the underside of the wings is brown. So one moment you think you're looking at a moth, and the next moment, an open butterfly flashes a blue that would vanish if its scales were a few more nanometers apart. (In fact, the scales are even based in melanin, to absorb the other colors.)

The description was fascinating, the picture is gorgeous, and now I can't wait to see one in flight.