your tank is a ten gallon right? how many hermits did you have in there?
as dbacksrat said, they are very good scavengers...something to remember is that most hermits don't live more than a year or so and if they were big when you bought them it could have already been close to their time...chances are it isn't really your doing...but if you are concerned about it, check your nitrates, etc because they are more sensitive to those toxins than fish