This is the Woolly Bear or the caterpillar form of the Isabella Tiger Moth, Pyrrharctia isabella. This little insect overwinters in this form and survives when it is literally frozen solid. It survives being frozen by producing acryoprotectant in its tissues. In the spring it thaws out and emerges to pupate. Once it emerges from its pupa as a moth it has only days to find a mate. See Wikipedia: Pyrrharctia isabella.