How does a caterpillar morph into a butterfly

Just wanted to say this is one of my favorite SD articles. In fact, I read it to my daughter when she asked this question a few years ago when she was starting to get into biology. Even re-reading it now inspires wonder in how nature works. Thanks for the clear, easy to read, and concise description on this topic!

Link to article.

It makes me think about the evolutionary path these animals must have taken to develop such a complex arrangement - what forces pressured them to evolve in phases like this. Good stuff!