Fall Webworm Moth caterpillar - Hodges#8140 (Hyphantria cunea)

caterpillar info
http://bugguide.net/node/view/453
this is the northern version, it has a black head
southern versions have reddish heads and brown hairs

more about this webworm
http://hyg.ipm.illinois.edu/article.php?id=611

and more further down on the page:
http://matthewwills.com/tag/moths/