I am a holistic dog breeder and we have never seen another fleas since we started using DE. We did have fleas one time on a puppy we had purchased but we coated her with DE, kept her separate and the fleas were dead the next morning. There were a few who survived near her eyes but those we just plucked out with tweezers.
I think DE is the single most important thing that I use for my animals. It truly is an amazing thing.