Okay, this is a pretty big segue: I was watching a video of some C&W fiddler (not my normal fare) and there were many hairs broken on his bow. It made me wonder how many of those hairs can be broken or missing before something needs to be replaced? I’ve not seen this happen in a classical concert, though it probably does, but as some point those little butters need to be restrung as well. Does this happen to violinists like Anne Akiko Meyers?
Yep, it happens to nearly every violinist or fiddler, especially if they have a heavy handed bow arm. Once about 1/3 of the hair is gone, by breaking (or being eaten by mites!) the bow should be rehaired. Depending on which side of the bow the hair is breaking, but usually the "playing side" facing the player, dictates if the bow will curve over to the opposite side and allow the hair to get pinched between the bow stick and the string. If this happens, it's sort of a cascade effect and more hairs get broken.