Throughout the summer at the Brooklyn Children’s Museum, we hold a public program every Tuesday at 2:30 called “Extraordinary Laboratory.” This inquiry-based science lab allows kids to take their learning in any direction that suits their interests. We provide microscopes, magnifying glasses, and an array of fascinating specimens on a particular theme. It’s their job to run wild with their own observations and scientific questions. Sometimes we discover answers to their quandaries and sometimes the kids take their questions home as mysteries to be solved with a little library or internet research.
This week, the theme of our lab session was bugs. We offered all sorts of dead bug specimens to observe under a microscope: everything from dragonflies to water beetles, bees to butterflies. The specimen that most captured the junior scientists’ attention was the wing of a blue morpho butterfly. Every time a kid put their eye up to the microscope, we’d get a chorus of “Whoa!” “Wow!” “Awesome!” “So cool!”
A butterfly wing is covered with hundreds of brilliantly colored scales. When the kids handled the wing specimens, they found a bright blue powder left behind on their fingers; the tiny scales had fallen off the wing. Throughout a butterfly’s life, these scales rub off from daily butterfly activities and cannot be regenerated. The brown patches in these pictures show where the shingle-like scales are missing. One child looked down at their finger and exclaimed “The spots on the wing look like glitter!”
Blue morpho butterflies, like some other species of butterflies, get their brilliant blue color from iridescence rather than pigmentation. Pigment color works by absorbing certain wavelengths of light on the color spectrum and reflecting others back. For instance, the chlorophyll pigment in plants absorbs all wavelengths of light except green which is reflected back to your eye.
Iridescence is special because it’s all about reflecting light waves multiple times. Within each tiny butterfly scale are lots and lots of semi-transparent surfaces for light to pass through and reflect off of. These surfaces are stacked with equal distance between each layer so that each reflected blue light wave lines up perfectly with the other reflected blue light waves, a phenomenon called constructive interference. The result is a bright amplified color!
- Image from www.HowStuffWorks.com
There is no blue pigment in the scales – that's right - there is not a single bit of blue pigment in that super bright blue wing! Because what you're seeing is light bouncing off tiny clear cuticles inside the scale, the color can shift or even disappear depending on how the light is bouncing from the scales to your eye and which light waves are being reflected multiple times in perfect sync! When you look at the butterfly wing from the side, you will see a shorter wavelength violet color. When you light the wing directly from behind, the blue light waves become completely jumbled with other light waves and the blue color disappears!
Remember our series on biomimicry? Researchers in nanotechnology study blue morpho wings and are attempting to mimic their iridescent scales for use in security. The goal is to create tiny materials that reflect light in the same way and could be used to make counterfeit-proof money, passports, and IDs.
At $129 a pop, these microscopes are a bit of an investment, but we've found them to be durable and really easy to use for ages five and up. If looking at iridescent specimens through a microscope isn't an option, don't fret, stay tuned to learn how to explore iridescence in other ways!