It is fun reading your posts on facebook. I read the butterfly story and like it very much. What you speak of makes a lot of sense and is a good lesson.
I would like to make one comment though, about the biology of butterflies, which most people forget once they leave school. Butterflies FORM a chrysalis, not spin it. (did you know the pupas already have wings just under their outer layer, what we would call skin, which are forced to the surface just before the chrysalis is formed?). Some types of moths SPIN cocoons, but most form a chrysalis like butterflies.

Just thought you would like to know.