Bow bugs are to bow hair as woodworm is to wood. They are tiny grubs that eat bow hair. If your hairs keep breaking, take a closer look. If the ends have been nibbled, then look at the bow - or more usually the case - and see if you can spot a white grub, about 2mm long. If so, vacuum out the case, and you can get a treatment dust for the bow. Ordinary clothes moths will sometimes get into a felt case, causing similar damage. Moth balls or treated paper are best protection for this. Bow bugs are not, generally, a problem where the bow, or case containing it, is in constant use.