
Browntail Caterpillar - Euproctis chrysorrhoea
This is a non-native species, introduced from Europe. It's a forest pest and feeds on 26 different genera of trees, in 13 different families!
It is reportedly only currently found (in the US) on Cape Cod, MA, and a few islands off the Maine coast in Casco Bay. But, I found it inland in Maine, although within 30 minutes of the coast.

The brown-tail is a moth of the family Lymantriidae. It is distributed throughout Europe. It is found in North America only on the coast of Maine and Cape Cod where it is considered an invasive species that arrived in the U.S. in the 1890s on nursery stock coming from Europe.