I use it for ant control. Googled and found this about use for fleas (scroll down a little). http://wolfcreekranch1.tripod.com/no_flea.html
One thing to remember when using, for oneself or animal, is to avoid breathing in the dust or getting it in the eyes. Ingesting is safe so if your dog or car licks it there isn't a problem (some people put it in food for worm control)