We found this 2 inch long caterpillar on our front steps yesterday. It is mostly grey with faint tan stripes and russet/orange spots where the very long hair tufts emerge. Picture 2218 is very out of focus but shows how the long hairs look like the fringes of a rug. I believe the caterpillar may be getting ready to molt or pupate as it has started to spin long spiderweb-like strands arond it’s enclosure. It might have fallen from the nearby linden tree (which just finished flowering) or come from some of the plants under the tree which include rudbeckia, hosta, creeping phlox, liatris, pansies, lavendar and purple coneflowers. We live in Southeastern Wisconsin.
This looks like the pestiferous Gypsy Moth, Porthetria dispar, to us.