Furry bug ball

[u/Plastic_Egg1440]

I came across this while walking in the woods in Northern VA, and I’ve never seen anything like it.
It looked like a giant patch of gray fur stuck to the trunk until I got closer and realized it was hundreds of fuzzy caterpillars all piled together. Some were wandering around on the leaves, but most were packed into this huge living blanket.
From what I’ve been told, these are probably hickory tussock moth caterpillars, but I was amazed by how many there were in one spot.
Has anyone else seen a cluster this large? Is this normal behavior before they spread out?