What happens inside a pupa stays inside a pupa. Or it used to, anyway. Until recently, when special x-ray imagers were turned on a developing butterfly to elucidate its metamorphosis.
the process of caterpillar-to-butterfly is a messy one. An overfed worm not only has to convert a lot of the stored energy it gathered stuffing its face for a few weeks into new body parts, it does so by essentially dissolving much of its body and reforming. The pupa isn’t so much a dressing room for a beautiful diva as it is a bag to keep all the goopy globs of proto-butterfly from dripping on the ground. Sounds like both butterfly and human puberty involve a mess of bodily fluids and hiding in your room.
That’s what most biology books would have you believe anyway. This new work (written up in great detail by Ed Yong) demonstrates that while there’s still plenty of goop-globbing, quite a few structures remain intact, migrating and growing into adult forms in a more traditional way (like those blue circulation vessels). For the insect nerds in the bunch, this technique doesn’t revolutionize metamorphosis or anything, but it’s a view inside that most of us have never gotten.
And quite a view it is.