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 for a few hours to allow it to fumigate.
- The next day leave the case open in the sun for a little while so that it warms up a little. Note: don't let your case get too hot.