On days 14-17, our caterpillars crawled up their sticks (with one going up the side of the jar instead) and assumed the "ready position", as I think of it. Each one makes a little silk pad to rest its back end on and also spins two silk strings to hang its top end from. Then it scrunches up (it really does look smaller than before) in the shape of a comma or apostrophe. It hangs there for about 36 hours, occasionally wiggling. See the one farther down the stick? It's in a more classic semi-upright position than the top guy, but I didn't get a good enough picture of that one.
After the allotted time has elapsed, the final molting occurs. The [looks like a caterpillar] wiggles and shakes off the last skin.And from inside that skin appears the chrysalis!It is so much more dramatic than watching the spinning of a cocoon. One moment it's a caterpillar, and the next a chrysalis. Several years ago we actually caught that moment on video, but it's not digital so I can't show you.You can still see the silk strings holding it in place.If you get an early "batch" of caterpillars (say, July), they'll emerge as butterflies in the same season. That happened to some at my sister's house this year. Ours almost always appear later (the final chrysalis formed September 17th), and the chrysalises in real life would overwinter outside with the butterflies emerging in the spring. The Family Butterfly Book states that overwintering species can be kept in the refrigerator and removed about 30 days before it's time for them to emerge. We've had some success with this (and some failure, too).