My dog brought the little fockers in several months ago, and the things loved my ferret. I had to apply the Frontline every three weeks for 9 weeks...it didn't maintain it's month long protection for the amount of fleas. By the end of the 9 weeks, the dog and ferret were clear and the house was also. Now a monthly application of frontline is enough. Well worth the expense to save your sanity and your cats fur.