the caterpillar's internal organs liquefy to build the new butterfly body

perhaps even weirder, it would appear as though memories of being a caterpillar are preserved:

The researchers trained the caterpillars to dislike the smell of ethyl acetate, a chemical often found in nail polish remover.

They did this by giving the caterpillars little electric shocks every time they smelled the chemical. Soon, these caterpillars were trained to avoid that smell because it reminded them of the electric shock.

They let the caterpillars transform into adult moths, and then tested the moths again to see if they still remembered to stay away from the ethyl acetate smell.

And guess what? Most of them did! The scientists had shown that the memories of avoiding the bad smell experienced as a caterpillar had been carried over into the moth stage.

The study showed that memory, and therefore the nervous system, stays during the complex transformation from the caterpillar to the adult moth. So while a moth or butterfly may not remember being a caterpillar, it can remember experiences it learned as a caterpillar.

https://theconversation.com/curious-kids-do-butterflies-remember-being-caterpillars-99508