Not a Metaphor: A Whole New Way to Watch a Caterpillar Become a Butterfly

Scientists use CT scanning technologies to better understand the insect world.
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A painted lady butterfly, in adult form (Shutterstock/Gary L. Brewer)

The caterpillar-into-butterfly evolution is nature at its most literary. Egg, to larva, to pupa, to rainbow-winged adult -- a transformation that is at once an embodiment of, and an allegory for, progress itself. A bildungsroman that happens, in this case, to take the form of a living creature.

It's a narrative arc, though, that has always been a little bit enigmatic to the scientists who want to understand it in detail. Entomologists have traditionally relied on dissections of species at various stages in their life cycles to understand insects' metamorphoses -- a method that has been time-consuming and labor-intensive for humans, and, for obvious reasons, even worse for the insects in question.

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The pupa, as imaged on day 1 of the researchers' trials (Tristan Lowe via Live Science)
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The pupa, as imaged on day 14 of the researchers' trials (Tristan Lowe via Live Science)

Now, though, two scientists at the University of Manchester have developed another way to study the life cycle of insects -- and it involves common imaging used in human medical practice. The researchers, Russell Garwood and Tristan Lowe, captured images of the metamorphosis of the painted lady butterfly with a Computed Tomography (CT) scanner -- a device with a resolution capable of imaging insects as small as 0.2 inches in length.

The team described the technique in a paper just published in the Journal of the Royal Society Interface.

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Renderings of the scans: By the time the butterfly nears completion of metamorphosis, the eyes, gut structure, and antennae are visible. (Tristan Lowe via Live Science)

To take their images, the Garwood and Lowe hung their sample pupas inside drinking straws and then slowly spun the straws around. From there, their CT scanner took some 2,000 X-rays, documenting the physical changes that took place as the pupas grew and, finally, burst out of their chrysalises. The machine rendered images of the butterflies' developing tracheal airways. And their antennae. And their midguts. It captured views of butterflies-in-process that were never before possible to see or create. 

And it found, among other things, that the creatures' tracheal systems may undergo less remodeling in the pupa stage than we previously expected -- a significant finding, since technological limitations have previously made insects' tracheal systems overall "an often-understudied character system in development."

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Renderings of the pupal development process based on CT images (Tristan Lowe)

But the CT scanning technique, the researchers say, could also have broad implications when it comes to biological research. In the wake of the alarming collapse of bee colonies, it could help scientists understand how pesticides might be affecting the anatomy of those crucial pollinators. It could answer questions about how genetic manipulation affects the development of the fruit fly. It could help us, overall, to better understand the insects that comprise as much as 85 percent of all the animals on the planet. "Insects are the main pollinators for the majority of our crops," Garwood put it, "so understanding what causes them to become ill is critically important."

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Megan Garber is a staff writer at The Atlantic.

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