Nice spotting!
This cool moth is one of two species of Slug Caterpillar Moth, either Euclea nanina – Nanina Oak-Slug Moth - http://mothphotographersgroup.msstate.edu/species.php?hodges=4697.1
or Euclea delphinii – Spiny Oak-slug Moth - http://mothphotographersgroup.msstate.edu/species.php?hodges=4697
Apparently these two species can appear virtually identical in some areas so I will leave it up to you to decide. You may want to consider submitting this to a site for ID but I am not sure they will be able to help more. It might be worth it.
A little more info:
http://bugguide.net/node/view/424
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