This is a Tussock Moth caterpillar, but I'm not sure which one. There are quite a few Tussock Moth species, including the banded, spotted and milkweed. I have a feeling this is the Milkweed Tussoc Moth (Euchaetes egle). If so, it only eats Milkweed, in the process absorbing cardiac glycosides that are retained through the adult stage. In other words it becomes poisonous to birds and other predators, and the bright colors and fierce look remind them of this.

Joey Anderson, 14