Diatomaceous Earth (D.E) is a naturally occurring, soft, siliceous sedimentary rock that comes from the fossilized remains of diatoms, a type of hard-shelled algae. When used internally in dogs and cats, D.E. can work as a natural dewormer and control internal parasites. It can also improve coats, appetites, metabolism, and digestion. For external use, it is a natural and non-toxic means of controlling external parasites on dogs and cats, such as fleas, ticks and mosquitos. Diatomaceous earth has microscopic, sharp edges that can damage the exoskeletons of insects and lead to death.