The transformation from caterpillar to butterfly usually happens quietly, inside a firm opaque husk that protects the pupa as it slowly forms its showy wings.

Back in 2015, at a summer course in Woods Hole, Massachusetts, some graduate students had a relatively simple idea that would enable them to get a closer look into this metamorphosis.

In the lab, graduate students Julian Kimura from Harvard University and Ryan Null from the University of California Berkeley made a small incision into the side of a caterpillar and pulled out the blob of cells that normally form the forewing in a butterfly.

After this surgery, which doesn’t hurt the caterpillar, they let it pupate—but the cells they removed created a clear window for a real-time view of the colorful wing formation.

Time-lapse video from Berkeley graduate student Aaron Pomerantz, who now uses this technique to view real-time color formation in butterfly wings for his research, shows off this process for the first time.

WINDOW OF OPPORTUNITY

Describing his video, Pomerantz notes that while other researchers have tried to peel wings back during pupation, this method is a bit simpler.

“Normally, the pupae are covered by a thin cuticle…we are just removing a few cells to create this window,” he says.

Taking one image every 20 minutes, Pomerantz has put together nearly 1,000 images to encapsulate eight days of butterfly pupation—and the transformation is magnificent.

And in case anyone is concerned about what happens after the video, he explains, the three-winged butterflies that develop from these experiments go on to live out their days in a Berkeley greenhouse. (Read more about a butterfly that looks like a dead leaf.)

LIVING COLOR

But what is the point of caterpillar surgery? “This is documenting structural color being made,” explains Pomerantz. Some colors in bird and butterfly wings, like black or yellow for example, are created by pigments. Blue, on the other hand, is what is known as a structural color that is created by the interaction of light with tiny nanostructures in the wing.

Watching the wing color form in real-time shows how the change in wing thickness is creating vivid blue structural color. (Read more about why butterflies are so colorful.)

“It was a happy accident in the lab that opened up a different avenue to study this process,” Pomerantz says. “It’s the first time anyone’s ever taken a crack at looking at structural color this way.”