Diatomaceous Earth (food grade) has been used by farmers for years.  It is a great cure for fleas and scabies - the "earth" (the powdered skeletons of Diatomes) dries out the exo-skeletons of insects.  It is edible, and can be dusted on animals for flea control, and can be added to the food to remove worms.  It is full of minerals, so good for you and the earth.