This is the best picture I can get of this (and others) on Joe Pye Weed. What looks gray is actually black. There are several in the early AM but as the sun moves around they disappear, then back in the AM.
I'd sure like to see other images....perhaps of true color. It's one of the many tussock caterpillars but can't tell you which one from that image. Let's see if anyone else can.
Tussocks need to be handled with care, by the way. Those rows of tussocks contain urticating hairs. Their stings don't pack a huge wallop, but can be a little painful.
Yes, Rhizo 1, it is the Milkweed Tussock. Thank you for the warning. I will just let them be!!
Gotta love Google :-)
Here is a link that might be useful: Milkweed Tussock images
A beautiful caterpillar.