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A caterpillar hatches from an egg, makes a cocoon, and emerges a fully-grown, beautiful butterfly. But, during its time in the cocoon, the caterpillar melts its body into bug goo... then even weirder stuff happens.

Hosted by: Olivia Gordon
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Olivia: You’re probably familiar with the basic life cycle of moths and butterflies: an egg hatches into a caterpillar, which becomes a pupa, which then transforms into a fully-grown moth or butterfly. But that transformation isn’t easy: if you sliced open a pupa at just the right point, you’d find nothing but bug soup.

Caterpillars grow the beginnings of their adult body parts before they even hatch. They have these tiny clumps of cells called imaginal discs spread around their bodies, and during metamorphosis, each disc develops into a different part of the adult butterfly or moth.

When a caterpillar becomes a pupa, it releases enzymes that dissolve almost all of its tissues. Only the imaginal discs, plus certain muscles and portions of the nervous system, survive. The rest of its body basically melts into goo.

This protein-rich slurry helps fuel an explosion of new cell division, as the imaginal discs grow into full-fledged wings, eyes, and legs for the adult insect. But even though they almost totally dissolve and rebuild themselves from scratch, adult moths can actually remember things from when they were caterpillars.

In one study, researchers gave mild electric shocks to tobacco hornworm caterpillars, a type of moth, while exposing them to specific smells. After metamorphosis, the adult moths still avoided the smells they’d learn to associate with unpleasant shocks. So at least some of the caterpillar’s brain seems to stick around through metamorphosis, even as most of its body dissolves.

Even though metamorphosis is a complicated process, we know that it’s helpful for insect species. The total rearrangement of body parts means that adults and young can rely on different food sources. Usually caterpillars eat leaves, while butterflies and moths specialize on nectar. Preventing different life stages from competing for the same resources gives these insects a big evolutionary leg up.

We’re still not entirely sure how metamorphosis evolved, though. One theory, which has since been discredited, suggested that metamorphosis became a thing when an insect that flew and an insect that crawled happened to mate. Instead, it probably evolved gradually from less-complicated forms of development.

So, no matter how metamorphosis evolved, it does make moths and butterflies super hardcore. They might look delicate and pretty, but those critters dissolved their own bodies and survived.

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