I've been getting my hives ready for winter, and noticed four hives, of twenty, with a pile of dead bees on the screened bottom. (Pile defined as screen almost completely covered with bodies) I haven't thoroughly then in a while, as they have been bringing in pollen. Could this just be a build up of bodies, and since I run top entrances, maybe they can't easily remove? These hives are weak now so I combined. Tks for advice.