It looks like a monkey slug to me, which is the caterpillar to the hag moth. http://www.whatsthatbug.com/2005/09/20/hag-moth-caterpillar-or-monkey-slug/ Abusive comment hidden. (Show it anyway.)
http://www.whatsthatbug.com/2005/09/20/hag-moth-caterpillar-or-monkey-slug/