bought some pet grade diatomaceous earth (at Western Farm). They also carry D.E. for chickens!
Interesting, you can give it to pets (dogs/cats) in their food to control internal parasites (worms, etc.).
Very happy with the results and also happy that it aids in combating tapeworms - so when the cats lick it off, as they will, it then goes to work against the tapeworms (which cats get from ingesting fleas!)