Thanks so much! I figured it was a swallowtail because we have a lot of them around the house - will this one create a crysalis on the plant? You mentioned you had taken it in for rearing - can I do the same and what would I do? Thanks again.

I suspect it will pupate somewhere on or near the food plant. There are some hints for rearing butterflies at http://www.rearing-butterflies.com/. As long as you continue to supply them with access to food they should do fine. I usually put them in a large jar with netting over the top. In a jar, you have to make sure it doesn't get to moist inside. An open rearing cage is better, and one with a growing larval food plant is best.