In a first, scientists captured growth of butterfly wings inside chrysalis on video - Ars Technica

Now, a team of researchers at MIT have captured on video the unique structural growth of butterfly wings—continuously, as a butterfly develops inside its chrysalis—for the very first time.

As I've written previously, the bright iridescent colors in butterfly wings don't come from any pigment molecules but from how the wings are structured.

Essentially, they form a diffraction grating, except photonic crystals only produce certain colors, or wavelengths, of light, while a diffraction grating will produce the entire spectrum, much like a prism.

Also known as photonic bandgap materials, photonic crystals are "tunable," which means they are precisely ordered in such a way as to block certain wavelengths of light while letting others through.

First, the researchers exposed the forewing by removing part of the cuticle with a scalpel; the pupae were anesthetized for this process.

Once again, the researchers used a glass coverslip to protect the exposed wing and provide a window into the chrysalis, sealing the window in place with dental composite.

However, the researchers needed a special kind of imaging to capture the wing formation, since simply shining a wide beam of light on the wing could damage the cells.

The solution: speckle-correlation reflection phase microscopy, which involves shining many tiny points of light on specific points on the wing.

"A speckled field is like thousands of fireflies that generate a field of illumination points," said co-author Peter So, one of three experts in this imaging type of imaging who collaborated on the experiments.