When I got home from work the next day, caterpillar #2 was missing! It had crawled out of the box! Luckily I found it close by, but already attached to the underside of a page of junk mail. I didn't dare disturb it, so I carefully cut out the piece of paper it was stuck to, and taped it inside the box. I later learned from reading that the caterpillar will leave the milkweed and crawl 30-40 feet away when it's ready to pupate.
My photos may be a bit fuzzy due to low lighting. I didn't know if a camera flash would upset the natural process. But the chrysalis, or cocoon, is still pretty distinctive. Caterpillar #2 is also a chrysalis now (more photos soon), but the baby caterpillar is gone. Although it had plenty of milkweed to eat and didn't seem big enough to start its cocoon, it disappeared from the box.
The entire caterpillar-to-butterfly metamorphosis takes only 9-14 days. You can read more here: