Possibly Obscure Sphinx Caterpillar:

Giant caterpillar in southwest Florida
Location: Corkscrew Swamp in Southwest Florida
December 30, 2010 2:50 pm
Hey…
I found this caterpillar in Corkscrew swamp near Naples, FL. It was late November and the caterpillar was in a tree about ten feet off the ground. It was about 5 to 6 inches long. I thought it was a branch but then it started moving. Im not sure what type of tree was feeding in. Is this some type of giant sphinx caterpillar? I’ve looked all over for his ID but cant find anything. This is probably the largest caterpillar I have ever seen.
(PS i got your book for Christmas and love it!)
Signature: Sammy

Hi Sammy,
It is difficult to be certain, but we suspect this may be an Obscure Sphinx Caterpillar, Erinnyis obscura, based on a photo posted to the Sphingidae of the Americas website.  Knowing the food plant is often a big help in caterpillar identification.  We will try to check with Bill Oehlke to see if he agrees with our tentative identification.