Flashes of orange and metallic blue shift and change in the morning air; waves of sunlight landing on the scales of their wings and scattering colors like a prism.
The Texas Butterfly Festival has come and gone, but the shimmering colors of a butterfly’s wing continue to resonate in the minds of their endless fan club.
Monarchs, malachites, gulf fritillaries, Mexican bluewings, blue morphos – they all wear a distinctive color scheme which distinguishes them from all others. Butterfly lovers can quickly identify butterflies by their unique markings.
But do we know how they get their colors?
Butterflies have a complex anatomy filled with chemoreceptors for taste on their feet and smell throughout their bodies.
Every part is a new journey through nature’s intellect.
The wings themselves have a clever assemblage that multitask for many purposes: veins pump fluid through the wings to gather heat, and the colors are used as camouflage, to warn off predators, signal other members of their species and attract mates.
The colors come from two sources: pigmentation and scales.
Most people understand pigmentation very well, but the scales of a butterfly’s wing have a more intriguing kind of structure and functionality, said Prof. Matthew Terry, associate professor in the biology department of the University of Texas Rio Grande Valley.
Scales, made of a carbohydrate called chitin, refract different bands of light which create constant changes of colors and patterns like a kaleidoscope, pieces of color splitting and coming together and spinning again.
“Refraction is something similar to what we get in a prism in which you get white light split into its components,” he said. “You can do that through different planes like in a glass prism. It can also occur through very small regular structures. Those are almost like a ladder but at the micro level. The light gets essentially split into its different wavelengths, which is essentially what iridescence is.”
Now, that’s fascinating enough, but it gets better.
A complex tapestry of disciplines – physics, chemistry and biology just to name a few – emerges in a feat of engineering much deeper than any refined study.
“With refraction, if you change the angle, you’ll see the different colors kind of play across,” Terry said. “A place that was once green, you change the angle, and it looks reddish or yellowish. That’s iridescence rather than simple light reflection.”
The hard science described here barely touches on a butterfly’s power.
Beyond the science of scales and refraction there is the passion, the nuance and the intimacy that touches everyone.
Writer Jenny Oh in the online publication KQED describes the work of Nipam Patel, a professor in the molecular and cell biology department at the University of California, Berkeley. The 2014 article refers to Patel’s study of the thousands of tiny cells, known as scales, on a butterfly’s wings.
“From a distance,” she writes, “the rows and rows of scales look like vivid patterns that decorate a butterfly’s wings. But up close, each scale is like a dab of paint in a Pointillist painting.”
Some butterfly scales are colored by pigments, she writes. However, others rely on something called “structural color,” the production of color by tiny elaborate shapes that reflect and bend light. One color often created through refracted light is blue, as most animals can’t produce that color as a pigment.
How that light refracts depends on the specific structures of individual scales, Terry said.
“It will depend on the space between those small structures that are causing the iridescence, how wide that spaces is, how widely distributed those organs are,” he said. “It could be also that you’re seeing a combination of pigmentation and iridescence. You might see an underlying color that doesn’t change much, but the overlying effect, you can get both at the same time.”