I've never heard of monarchs overwintering here in MS, but I have heard of them overwintering in southeastern Louisiana, somewhere south of New Orleans.
Does the swallowtail have a horn on its rear end? If so, it's probably a tersa sphinx moth caterpillar. I've still got some palamedes swallowtail cats - yesterday one of them "spilled its guts" and turned yellow, so it'll be pupating today. When the temps go below 40 degrees, I bring them into my unheated guest room, then bring them back out when the warm weather returns.
Here's a picture of a brown and a green tersa sphinx cat -
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And here's a picture of a palamedes swallowtail cat - they're usually the only swallowtails that I find this late in the year -
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MissSherry

Thanks MissSherry, it is indeed the spinx moth. The pics help out so much. I have never mastered the art of posting pics but one day I will and then I can share with you. How about this nasty weather we're having? It has sure put a damper on going out to work in the garden hasn't it. Again thanks for taking the time to help; you are just the best. Butterflutter

You're welcome, Butterflutter!
I just looked at the radar, and it looks like there's a lot of heavy rain in the McComb area - we're supposed to get it later tonight and tomorrow. I hope some drifts up Atlanta way!
MissSherry