[Karen K]

Again, always use FOOD GRADE. The DE for pools and such contains toxic chemicals.
DE is used in grain silos to control weevils & such. It can be taken internally for parasites but will not kill every type of parasite so research this and also the amount to use. It does not require a large amount of DE.
DE kills fleas because it kills exoskeleton pests which also includes roaches, spiders, etc.
It kills them because the sharp edges of the material (think really tiny tiny sand) of the diatoms from which it is made puts cuts in exoskeletons and the bug dehydrates to death.
Works great on Palmetto bugs (think huge roaches) in Florida. I have used it on kittens & puppies. Expose the skin by holding back the hair and powderpuff it on the area around the neck and tail (fleas favorite places). Eventually the fleas will crawl over the area and they are goners. No need to create dust while applying it. The dust is very dangerous if inhaled as it will also cause tiny cuts in lung tissue of any mammal. DE does not kills bugs by chemical action but by a natural method which does not harm mammals as long as they don’t breathe the DE dust in.