We’ve all “turned green” after a night on the town, but for butterflies in the genus Morpho, alcohol quite literally reveals their hidden colors. Pour a bit of isopropanol on their wings, and the butterflies change from iridescent blue to a deep, forest green. That’s interesting enough, but what happens next is even better: as the alcohol evaporates, the wings return to the exact shade they started with. This is possible because, contrary to what your brain is telling you, they aren’t actually blue.
You’re being duped by a light-bender.
Morpho wings are some of the most brilliantly-colored structures in the natural world, but they contain no blue pigment. In fact, you might be surprised to find that most of the animals you associate with the color blue aren’t blue at all.
This peacock’s feathers, for example, are actually a mixture of black, dull yellow, red and brown.
This blue jay’s, too.
Even the plant that produces the most intense blue color in the world—a small, African berry—contains no blue pigment whatsoever. So what’s going on? The iridescent color you see is the result of “constructive interference,” a structure’s ability to cancel out certain wavelengths of light.
Butterfly wings look smooth to the naked eye, but a closer inspection reveals that they’re actually covered by thousands of modified hairs, known as scales. Each scale contains unique ridges and grooves that act like tiny prisms when light hits them at the right angle. In the case of the Morphos, the scales are perfectly shaped to trap all wavelengths of light except blue, the only color that hits your eyes.
Take a look at what happens when the wing-scales of a different insect, a uraniid moth, are viewed under a microscope:
“The green scales on the moth turn purple when we zoom in,” explains entomologist and photographer Aaron Pomerantz, who spotted the stunning creature on a riverbank in Peru. “This is likely due to the structural nature of the scales – light is coming in at a different angle and thus changes to a purplish color.”
The same thing is happening in the alcohol experiment above. When liquid hits the butterfly wing, it floods the tiny nanostructures, temporarily changing their shape. This scrambles the way they interact with incoming light. As the structures dry, their shape is restored, and they resume refracting blue light.
As a general rule of thumb, pigment produces “hot” colors like red and yellow, whereas structural color produces “cool” colors like blue, and violet.
Nature is one step ahead, but understanding this evolutionary workaround could lead to some interesting developments in human tech. For example, in 2013, research and development firm NanoTech Securities managed to recreate the effect by punching 500 million—yes, MILLION—carefully crafted holes into a piece of plastic. Check it out in this video from Veritasium: