Cut the milk weed plant and place it in a jar of water. The caterpillar will eat voraciously and grow quickly. You may need to pick more milk weed leaves for him to eat.
When he reaches his ultimate size, he will look for a quiet place to make his chrysalis. At this point it is good to have him trapped in a jar because he will roam out of sight! An ideal system is a large gallon size jar with a small baby food jar of water inside for the milk weed. But if you don't have a jar big enough, a box with a screen top so you can watch him, works as well.
The caterpillar will hang from his tail with a little webbing and then change into his lovely green chrysalis. Two weeks later he will emerge as a beautiful monarch! Release him to the outdoors to begin his long flight to Mexico for the winter. To learn more about these fascinating insects, check out this site here. We've been enjoying some of the library books about butterflies but nothing beats watching it first hand.
Give it a try, and maybe it will become a favorite memory for your children as well. (And you don't have to have a child around to enjoy it!)
The photos in this post are mostly from last year's butterflies, though a few are from our present caterpillar!