‘Christmas Trees’ light up butterflies
Many artists struggle to illustrate the stunningly beautiful wings of iridescent butterflies, such as the blue morpho of South America. That’s understandable, because the iridescence is not due to a pigment.
Rather, the dazzling effect is known as structural colour, produced by light reflecting off the wing scales, producing constructive interference in blue light. You have to peer into the tiny nanostructure of the scales themselves to understand how it works. An electron microscope reveals structures “which can only be described as Christmas Trees”1 standing up from the surface of the scale, like a commercially planted forest, with the ‘trees’ (just one micron2 high) in orderly lines.
Light differentially reflects off the different structures within the ‘Christmas trees’, and this dynamically changes with the angle of view.3 Little wonder then, that artists cannot truly ‘capture’ the shimmering wings of an iridescent butterfly in flight!
What’s more, the wing scales have inspired scientists and engineers to design improved high-tech textiles, cosmetics, self-cleaning surfaces and security tags. At the forefront of these discoveries is optical physicist Professor Peter Vukusic of Exeter University. He recalls, “We shone a laser through a single one of those wing scales and we saw a wonderful diffraction pattern produced. I had goose-bumps along the back of my neck … It was a life-changing moment.” It certainly was, for Vukusic explains that now even the American military have become interested. They are looking to mimic the wing scale nanostructure to build better explosive-agent vapour detectors. As the test vapour displaces normal air from the air gaps between the ‘Christmas tree’ structures, the optical appearance changes accordingly.
So, butterfly wing scales are certainly not simple. As Professor Vukusic enthusiastically pointed out, “They are complicated. They are adapted to serve a set of complicated functions. The optical ingenuity that’s responsible for the appearances which we see is tremendous.”
Who is responsible for that “optical ingenuity”? The Psalmist certainly knew:
“O Lord, how manifold are your works! In wisdom have you made them all; the earth is full of your creatures.” (Psalm 104:24)
And the writer of Ecclesiastes, pondering the world around him, similarly praised God,
“He has made everything beautiful in its time.” (Ecclesiastes 3:11)
References and notes
- Bomford, A., Butterfly wings inspire cosmetics and bomb collectors, bbc.com, 9 July 2014. Return to text.
- A micron or micrometre (µm) is one-millionth of a metre. Return to text.
- For further explanation, see Sarfati, J., Butterfly-brilliance, creation.com/butterfly-brilliance, 1 January 2009. Return to text.