SGU Science Picture Of The Week: Wings & WIPs
What you see here is one of the most beautiful phenomena in nature, iridescence.
Iridescence is an optical phenomenon that is often called thin-film-interference. It is most often seen in the man-made and iconic parking lot puddle. The oil on the water is so thin it reflects light from both its top surface and bottom. That tiny tiny extra distance that the bottom light travels before it reflects towards your eyes causes it to be out of phase with the top-reflecting light. As this light interferes with itself, the colors implicit in the white light, reveal themselves to glorious effect.
A thin film of oil isn’t the only way to produce iridescence as evolution discovered quite some time ago. Many creatures and objects do it such as butterflies, beetles, shells, and even minerals. In these cases the ever-important light interference is caused by what’s called structural coloration. The vivid colors are caused by microstructures that manipulate light in various ways to produce a color explosion. Some animals like butterflies have wings consisting of many thin layers. This is thin-film-interference on steroids since there are so many more opportunities for interference to take place. When you add this to their natural pigment you often see colors that are combinations of both.
Other creatures create light interference from structures acting as diffraction gratings. These structures owe their abilities to their diminutive size on the scale of the wavelength of visible light. A peacock’s feathers produce iridescence this way. And there are yet other structures like crystal fibers, photonic crystals, and selective mirrors that all perform similar functions.
This brings us to the beautiful beasty pictured above. The striking colors on the parasitic wasp’s diaphanous wings seen here are the result of their extreme thinness producing, you guessed it, thin-film interference. These Wing Interference Patterns (WIPS) are only visible against certain backdrops with certain light patterns. The frequencies of light produced lack a pure red color which matches the range of light detectable by many insects. This leads researchers to suggest that these insects can use their WIPs for visual signaling. Some species display sexually dimorphic patterns meaning you can tell males and females apart by their WIPS.
So check-out all the wonderful and beautiful ways iridescence can occur and bring some color into your life.
Image Credit: Ekaterina Shevtsova of Lund University, Sweden.