Black Swallowtail Butterfly Emerges in Winter

We found a black swallowtail caterpillar in our garden last fall and put it in a jar to see if we could watch it go through it's change. It just "hatched" this week.

We live in central Minnesota, and the outside temps. are highs around 20 degrees and lows of about 0. I am afraid if we release him now he'll freeze. But I don't know what to feed (or how to raise in general) the adult butterfly. Any suggestions?? My kids are so excited, and I hate to tell them we have to let him go just to have him freeze to death.
Thanks.

Karen says
I live in Minnesota also and know how cold it is right now! The chrysalis you brought inside is the generation of Black Swallowtails that "overwinter" and hatch in the spring. Next time you could put it in your garage and bring it inside in the spring to observe it. Then after it emerges you can release it outside.

For now, you can feed the black swallowtail Gaterade, Juicy Juice or sugar water (boil water and add sugar to dissolve at 10 to 1 ratio - ex. 10T water to 1T sugar). Saturate a crumpled white paper towel with the nectar and place on a shallow plate or dish.

This book has detailed information on raising butterflies inside.