If you have opened your case after not playing for a while and the hairs are breaking it might be the work of the "Carpet Beetle Larvae". They like to eat horsehair when it's in a dark case. They tend to eat in one place straight across the hair, but I have seen violin cases that haven't been opened in decades and there isn't any hair that's longer than one inch.
If you look closely at the spot where the hair has broken most likely you will notice a slight divot out of the hair. Also, I think they must like the taste of rosin.
How to prevent bow bugs. If you are playing every day they don't seem to have time to eat the hair, so play daily. Keep unused bows out of a dark place and have them stored in a sealed plastic bow bag. If you don't have a bow bag, then wrapping the bow with cellophane plastic wrap should help protect the hair.
To clean your case I recommend using the following steps.
- Completely empty your case.
- Brush out the case with a good brush getting into all the little crevices.
- Vacuum out the case
- Spray lightly with a flying insect spray and then close the case and place it inside a large sealed trash bag. Allow it to fumigate for at least several hours.
- A flying insect spray puts out an Aerosol spray without leaving any residue, it is not a liquid stream.
- You only mist the inside of the case a little bit. Do not make the case wet.
- If you are unsure about what type of spray to use or how to spray the case, then just skip this step #4.
- The next day leave the case "without the bag" open in the sun for a little while so that it warms up a little. Note: don't let your case get too hot.