I think that this may be an early instar of a Gypsy Moth (Lymantria dispar). I tried to measure it and it crawled on my ruler.
http://bugguide.net/node/view/8780/bgimage
This page
http://www.inspection.gc.ca/english/plaveg/pestrava/lymdis/tech/lymdise.shtml states...
"Larva: The 1st (3 mm) and 3rd (7 mm) instars are black with long hairs; the 2nd instar (5 mm) is brown with short hairs. Instars 4, 5 and 6 are similar to each other and may be light to dark gray with flecks of yellow. They have long hairs that may be dark or golden and have 2 rows of tubercles along the back. Normally 5 pairs of blue tubercles are followed by 6 pairs of red, however variations are known to occur including all 11 pairs of tubercles being blue."