I recently disoverd that my cats have fleas. It was a pretty bad infestation and it was in the carpets too. I used borax to kill the fleas living in the carpet and vacume often. It seems to have done the trick. I am using Frontline on the cats and have found that it has really helped but hasn't completely killed the fleas. How long does it take for the fleas to die? This is appliation #2 and its almost time for another dose. I have enough Frontline for one more month and hope that it will finally kill the fleas.