This is a great question! Actually most of the parts (tissue) that we would call the brain in a caterpillar is broken down during metamorphosis and rebuilt in the adult butterfly. Remember we said most. The muscles are also broken down and rebuilt. This makes sense because of what you have probably observed – caterpillars crawl and butterflies walk and fly. They need different types of muscles for the different ways they move.
What is especially interesting is that the brain cells that aren't completely broken down are mostly the ones that send signals to the muscles to tell them to move. So even though the muscles in the caterpillar and butterfly are different, many of the brain cells that signal those muscles in the caterpillar will remain the same through metamorphosis and signal the new muscles in the butterfly. How neat is that?
To learn more about butterflies, try these links.
Blue butterfly image by Iaian Lawrie.
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Dr. Biology. (2017, May 12). Is a butterfly's brain the same as the one it had when it was a caterpillar?. ASU - Ask A Biologist. Retrieved December 3, 2020 from https://askabiologist.asu.edu/fr/node/3328
Dr. Biology. "Is a butterfly's brain the same as the one it had when it was a caterpillar?". ASU - Ask A Biologist. 12 May, 2017. https://askabiologist.asu.edu/fr/node/3328
Dr. Biology. "Is a butterfly's brain the same as the one it had when it was a caterpillar?". ASU - Ask A Biologist. 12 May 2017. ASU - Ask A Biologist, Web. 3 Dec 2020. https://askabiologist.asu.edu/fr/node/3328