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The Kid Should See This

Why Is Blue So Rare In Nature?

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Among living things, the color blue is oddly rare. Blue rocks, blue sky, blue water, sure. But blue animals? They are few and far between. And the ones that do make blue? They make it in some very strange and special ways compared to other colors. In this video, we’ll look at some very cool butterflies to help us learn how living things make blue, and why this beautiful hue is so rare in nature.

Joe Hanson talks with Smithsonian Curator of Lepidoptera Bob Robbins at the National Museum of Natural History to find out how butterflies use light to communicate, how blue animals are almost always not blue, and what exceptional creature has evolved a blue pigment. Come for the science. Stay for the joke at the very end.

blue morpho butterfly wing
Plus, from the video, re-read Hanson’s description of how structural color works:

The blue color isn’t from a pigment. The blue comes from the shape of the wing scale itself, and when I learned how this works, it kinda blew my mind…

If we zoom way in on a blue wing scale, we see these little ridges. If we slice across the scale, and look closer, we see those ridges are shaped like tiny Christmas trees. The arrangement of the branches is what gives Morpho wings their blue color. When light comes in, some bounces off the top surface. But some light passes into the layer and reflects off the bottom surface. For most colors of light, waves reflecting from the top and bottom will be out of phase, they’ll be canceled out, and that light is removed.

But blue light has just the right wavelength: the reflected light waves are in sync, and that color makes it to our eye. This hall of mirrors only lets blue light escape. There’s even a pigment at the base that absorbs stray red and green light to make the blue even more pure. That’s how we get this awesome iridescent blue.

blue jay wing

Next from It’s Okay to Be Smart: Go inside an ice cave to see nature’s most beautiful blue.

Then watch more blue morpho butterfly videos on this site:
• What Gives the Morpho Butterfly Its Magnificent Blue?
• Zoom into a Blue Morpho Butterfly
• Blue morphos emerge from their chrysalises

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