Insect Wings Are Rainbows of Color

Scientists in Sweden have found that a feature of transparent insect wings – their shimmering colors – may have a purpose.  They are not just accidental patterns like the rainbow colors of oil on water, but are stable structures genetically determined for insect recognition and mating.  They call them “wing interference patterns” (WIP) but their evolutionary explanation for them appears to be a work in progress (WIP).
    Publishing in PNAS,¹ the team said that these color patterns “have been largely overlooked by biologists” even though they have been known since before Darwin.  Like the oil-on-water effect, “These extremely thin wings reflect vivid color patterns caused by thin film interference,” but the effect in insects is not accidental.  “The specific color sequence displayed lacks pure red and matches the color vision of most insects, strongly suggesting that the biological significance of WIPs lies in visual signaling.”
    The patterns, they found are not just genetically stable, but are reinforced by additional structures, such as “membrane thickness, pigmentation, venation, and hair placement.”  They continued, “The optically refracted pattern is also stabilized by microstructures of the wing such as membrane corrugations and spherical cell structures that reinforce the pattern and make it essentially noniridescent over a large range of light incidences.”  Their paper is loaded with dazzling color images of various insect wings.  They feel this largely-overlooked feature of Hymenoptera (bees, wasps) and Diptera (flies) can serve as a species identifier and a potent source of experimentation on genetic control of wings.
    The authors had a lot to say about evolution.  They ascribed these coloration patterns to sexual selection, but it was clear their thinking was largely unformed and tentative: “The WIP is potentially a major contribution to the toolbox for evolution of small insects with transparent wings and thus an important piece of the evolutionary puzzle, they said at the end of the paper.  Apparently no other biologist has examined these features of insects before in evolutionary terms.
Update 01/13/2010: Live Science posted an article and photo album about this phenomenon that they said was “hidden in plain sight” from scientists.  One researcher at the University of Lund said, “one day you handle a specimen, which you may very well [have] seen before, and suddenly you notice the wing pattern, which is beautiful and perfect, like an art painting.”  A colleague responded when shown these patterns, “It was like the world I knew suddenly was turned upside down and a totally new character system was sparkling from every wing of the flies I had been working with for years without really noticing.”  But then he said, “We find it hard to believe that insects walk and fly around with wings that can be turned on to large (to them) flashing billboards without evolution picking up on it.”  The article later acknowledged that evolution of these art paintings is not straightforward from the evidence: “They also hope to learn whether evolution drives changes in the color patterns,” putting any scientific understanding into future tense.  For now, “The study is an example of old-fashioned science yielding new information,” he said.

1.  Shevtsova, Hansson, Janzen and Kj�randsend, “Stable structural color patterns displayed on transparent insect wings,” Proceedings of the National Academy of Sciences, print January 3, 2011, doi: 10.1073/pnas.1017393108 (open access).

One thing is clear: insects did not decide to “evolve” this capability, nor did “evolution” as if it was some purpose-driven goddess.  Yet again and again, the authors spoke of evolution as a purposeful agent with a toolkit for getting things done.  We need to kick some butt about misuse of terms in evolutionary theory.
    The patterns truly are beautiful; you should look at the images in this open-access paper.  In creation, things are often functional as well as beautiful.  You yourself should be useful as well as ornamental.  For a new year resolution, work on whichever part is not optimum.