Barb at the Handbook of Nature Study blog found out these two words are not interchangeable. From the Butterfly Gardening Glossary:
chrysalis - the pupa stage of a butterfly. The chrysalis is often mistakenly called a cocoon. The chrysalis forms when the butterfly caterpillar sheds its skin for the final time, and a hardened outer covering forms to cover the changing pupa inside. Chrysalis means gold in Greek. Many - though not all - chrysalises have gold spots or markings. pl - chrysalides, chrysalises
cocoon - the pupa stage of a moth. The cocoon is a covering that protects the pupa inside as it changes into a moth. Cocoons are formed from silken threads spun by the last instar caterpillar. Some species of moths will also incorporate leaves into their cocoons. After the cocoon is formed, the caterpillar inside will shed its skin for the final time, and a pupa with a hardened outer coating will form.
So now we know! I'm glad she took the time to research it out. I should have done a little more research before posting that Spunky was in a cocoon. But I know now. Spunky was in a chrysalis.