It is really the larva of the carpet beetle, and thrives on rosined hair and only in the dark. If the bow is used every day, the bug will not eat the hair. The fumes will kill existing larvae and prevent eggs from hatching. More bows are damaged by inept repair persons than by other accidents. Proper hair amount is essential.
Strong bows get more hair than weak ones.
Too much hair makes the bow sluggish in response. Too little hair produces weak sound. Hair, having been a living substance, lasts only six to eight months before becoming brittle. Frequency of installing new hair depends on use. It is common for very active players to rehair once per month.