Hag moth caterpillar or “monkey slug”, Phobetron pithecium.
This one was definitely a “lifer” — approximately 1.5cm long, this wandering, tentacled floofball is the hag moth caterpillar, or “monkey slug”, the larva of the moth Phobetron pithecium.
Like many things with inviting, fuzzy backs and adorable tentacles, this caterpillar is venomous — I’m actually having trouble finding out if it’s the tentacles, or the individual black “hairs” you can see in this photo that cause the “sting”, but petting this soft friend will produce stinging, itching, and possibly anaphylactic reactions, so these caterpillars are best enjoyed visually.
Hag moth caterpillar or “monkey slug”, Phobetron pithecium. 
Hag moth caterpillar or “monkey slug”, Phobetron pithecium.
There seems to be huge variation in hag moth caterpillars. As they grow older they seem to acquire more and more “arms”, change color from gold to red, etc. The tentacles are the identifying feature, though — no other caterpillar in North America looks quite like this. The adult moth is also furry, and a charming tortoise-shell pattern.
Hag moth caterpillar or “monkey slug”, Phobetron pithecium.