This could be either a Fall Webworm or perhaps a White Caterpillar - Spilosoma virginica. Checking with Bugguide.net, and I'm still not sure. The Fall Webworm descriptions show it in tents and not so hairy looking. But the Peterson Caterpillar book says there are black spots on each body segment, which seems to be the case here. This guy, believe it or not, was crawling all by himself on black pavement - at high risk of becoming some bird's dinner.
It crawled willingly on to this twig and held on for dear life while I carried it to house and camera. Can a caterpillar have acrophobia? When the pictures were finished, it gleefully scurried off into the grass.