I was taking photos by a stream when I saw a tree with these bits of "fluff" all over it... I took a leaf with me since I couldn't photograph it very well on the tree from where I was standing. I carried it around for at least 15 minutes before sitting it down on the ground to take a photo. I thought it was some sort of fungus. A friend thought it was a flower at first, then he said "I think it's alive!." We both stared in amazement as the "fluff" began moving across the leaf.... (I have since learned that this is a butternut wooly worm)