What you describe is probably moth nibbles. I have stored several hats together on a coat tree only to discover one with moth nibbles. The others remained untouched. The hat that was damaged was an inexpensive Solentino, made in CZ or Yugoslavia or somewhere like that. Maybe it has something to do with the wool content. Who knows? I've taken to storing my nicer hats in the box wrapped in the plastic they came with. Moth Balls are now an additive to my closet.