Re: Is a caterpillar transforming into a butterfly a chemical change, physical

Is a caterpillar transforming into a butterfly a chemical change, physical change, both, or neither? why?

Hi. We have quite a few answers in our archives that address the question of chemical and physical changes for different cases. Take a look at these answers (951513342.Ch, 964040935.Ot, 968982143.Ch, 958169312.Ch and 1236267954.Bc). From those answers, you can see that for the question of what is a chemical or a physical change can be a complicated question for a living organism.

So, it might be best to say that, like the lifecycle of any organism, the metamorphosis of a butterfly -- from embryo (egg), to larva (caterpillar), to pupa (chrysalis), to imago (butterfly) -- represents a biological change. The caterpillar, chrysalis, and butterfly look very different in size, shape and color, but from the organism's last moment as a caterpillar, to its first moment as a butterfly, it is made up of almost all the same atoms (I say almost because the chrysalis IS breathing during pupation). So, in that aspect the change between caterpillar and butterfly stage could be considered to be largely physical -- just the atoms of the chrysalis being physically moved around.

Of course, the molecules that those atoms are made into are quite different. Lots of hormones are produced to govern the development of the butterfly body, and lots of new structures (like wings) are built, which requires the breakdown and synthesis of lots of proteins and other biomolecules. So in that aspect, a lot of chemical changes are taking place.

You can ask the same question about the lifecycle of any organism -- when a person learns a new skill, have they undergone a chemical or a physical change? -- the mystery of the transformation from caterpillar to butterfly is that it takes place hidden within the chrysalis, where we can't see what is happening.

References:
Hetz SK. The role of the spiracles in gas exchange during development of Samia cynthia (Lepidoptera, Saturniidae). Comp Biochem Physiol A Mol Integr Physiol. 2007 Dec;148(4):743-54.