When I first saw these caterpillars I thought they were still in a silk cocoon, but looking closely it was just very dense long hairs. The Buff-tip Moth is a very difficult moth to see, as it looks exactly like a broken bit of branch from a birch tree, and blends in fantastically well (I wish I had a photo). They fly at night, making it even more difficult to find one resting in the daytime. Many hairy caterpillars can cause skin irritation, so best to never touch them.