If you keep bees then you are also keeping mites. The varroa destructor mite made its way to the US sometime in the 1980s and has been wreaking havoc on bees ever since. Much science, history and details aside, the jest of it is if you have a hive and are wanting to keep bees (and plan to have them survive and thrive) you will need to manage, control and therefore treat for mites.
