Thank you so much - I vote for Two tailed swallowtail!!!
I need to get a good larvae book - could not believe I couldn't locate this one, and also knew I had "seen pictures" of it ...somewhere!!!!!
My neighbor found it - just hunkering along on the grass, I believe...so no clue as to food source.
Those protuberances were going in and out of the head of the little guy - so strange to watch that going on!!! You could see moisture on them when you shifted it in the light...boy, I need to go back to school to learn some things about caterpillar morphology.
Vickie, it says Caterpillar hosts: Leaves of ash (Fraxinus), hop tree (Ptelea), and chokecherry (Prunus).
If you have any of these to feed him you can probably keep him. He'll make a chrysalis then become a butterly. He's a pretty thing, that's for sure!
On further inquiry, I learned the neighbors dog was rolling it along in the gravel ... I encouraged them to put him/her out in the "woods" - away from the dog. Those protuberances are called "osmateria" - my new word for the day, and are the source of the acrid smell. That you, Floridian, for the wonderful links that added to my knowledge base!!!