Annoying yes, but the optical marvels these insects show have not been lost on companies such as 3M, which have found ways to emulate insect iridescence in thin sheets of plastic, and artists such as Sydney-based designer Donna Sgro, who has made dresses using a high-tech material that displays a shimmering blue appearance even though there isn’t a molecule of dye in it.
Why do these jewel bugs look so much more colorful and shimmery — and, for the bug-lover, way cooler — than your average kitchen fly or dime-a-dozen gnat? The answer has to do with the way their fingernail-like exoskeletons transform visible light when they reflect it into our eyes and, also, how we perceive color.
All of the reds, greens and blues in your life correspond to specific wavelengths of light that stimulate the color-sensitive cells, or cones, of your retina, which then send signals to your brain. The wavelengths of these colors range from about 700 billionths of a meter on the redder side of the spectrum to about 300 on the bluer side. Things have specific colors because the materials they are made of, or are coated with, absorb different portions of the visible spectrum and reflect the rest. A leaf is green because its chlorophyll and other pigments absorb all colors except the green that reflects into your eye.
In addition to this absorption and reflection, the colorfest of the world’s most spectacular bugs — and even the ones in your own back yard — is often the result of other types of optical acrobatics, such as refraction and diffraction, which bust up mixtures of wavelengths into their color components.
Consider, for example, the Costa Rican beetles Chrysina aurigans and Chrysina limbata, which look like solid nuggets of gold and silver, respectively. Reporting in the journal Optical Materials Express, a team of chemists, physicists and materials scientists at the University of Costa Rica spell out how the optical bling of these beetles derives from dozens of thin layers of organic material with spacings comparable to the span of a single wavelength of light.
When sunlight enters the stack of layers, something quite eye-catching happens. At each successive layer, some of the light reflects back out, and some penetrates to the next layer. This results in a two-way traffic of light coming and going, with some wavelengths getting dimmed or canceled out by the process but many getting boosted, notes physicist and study leader William E. Vargas. The enhanced reflectiveness of these wavelengths looks to our eyes like shininess, and “this leads to the metallic appearance of the beetles,” he says.
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