caterpillars’ bodies “melt” almost completely before morphing into butterflies in the chrysalis.
In order for the change from a caterpillar to a butterfly to take place within the pupa, the caterpillar begins releasing enzymes that literally digest nearly all of its own body. What’s left inside the chrysalis is mostly just a very nutrient rich soup from which the butterfly will begin to form.
It was thought until very recently that the caterpillar was completely converted to goo, excepting certain special cells necessary to create the butterfly body parts. This idea has recently been debunked with researchers at Georgetown University proving that moths retain at least some of the memories they had when they were caterpillars. For this to be the case, at least some of their memory storing neurons must survive the enzyme digestion process. Further, these neurons must somehow be incorporated into the moth or butterfly’s brain, which is quite a bit larger and more complex than a caterpillar’s brain.
Also left within the goo are very tiny imaginal disks, which are similar to embryonic cells. These disks are actually present within the caterpillar its whole life, but they stop growing at a certain point in the caterpillar’s development and only start again when it is time for the caterpillar to morph into a butterfly. Once the proper time comes, the imaginal disks use the nutrients from the digested body of the caterpillar as they form into different parts of the butterfly’s body, with different disks forming into different tissues. For instance, there are imaginal disks that will form the legs, antennae, specific organs, etc. of the butterfly. There are even four imaginal disks that form wings. If one of these forming wings is removed, the other three will simply adapt to form bigger wings to compensate for the loss of the one wing.
Once the process is complete, the imaginal disks ultimately replace nearly every part of the dissolved caterpillar’s body with new “parts”, forming the butterfly.