this is a caterpillar known as spiny oak slug.  Many of these caterpillars  have a bit of venom in the spines which can deliver a stinging sensation when touched.  (I only know that because i could not help myself in touching it!)  The adult is a moth- brownish but still kind of pretty.  What a cool photo!  I am wondering if you might be willing to send me your shots to be used in an educational program in the future?  If so, my address is <personal data hidden>