Well, I am so NOT good at comparing photo's! I've searched through my book Butterflies of Florida and couldn't seen to find anything that matched. I started googling and found this site with different instar stages of the Luna Moth. Scroll down this page and look at the fourth and fifth stages:
http://entnemdept.ufl.edu/crea...
Or maybe the Polyphemus Moth?:
http://www.ag.auburn.edu/enpl/...
http://www.google.com/search?q...
I'm leaning more towards the resemblance to the Luna Moth Caterpillar but that may be because I just LOVE the Luna Moth and I've never seen one in person!
