I found this caterpillar on a trail in the North Carolina Appalachians (near Robbinsville). The closest match seems to be a satin moth caterpillar but their tufts of hair and pattern look slightly different, and I don’t think they are found in the US (seem to be mostly in Europe). Help!
With the help of a great taxonomist from Ohio State, I learned your caterpillar is called the black zigzag or tufted spruce caterpillar. It turns into a rather pretty black and white moth. The best ID is from moths because there is a lot of variation in the caterpillars.
It is common in the Smoky mountains, but not further south. It ranges from Canada south over the Great Lakes, west to Colorado and then south to Georgia.
The black zigzag lives in coniferous forests with the caterpillars eating fir, hemlock, larch , pine and spruce. They overwinter as pupae in leaf litter or soil. There are two generations in the Appalachians while only one north of there.
Moni has an ebook “Garden Insect Pests of North America – Pictures for Identifying and Organic Controls” Check it out!