I returned a book to the Fox Point library today. Since I still had a couple of brief chapters to go, I read them at one of the tables. A few feet away, one of the librarians was giving kids the 411 on the development of a monarch butterfly. They had a display with caterpillars in glass 'n grass, the difference between a cocoon and a chrysalis, etc. It was kind of a neat refresher course for me, too.
The caterpillars turn from green to brown to avoid being eaten. Birds are either fooled by this or are really good sports.