Fipronil 10% w/v + [S]-methoprene 9% w/v Spot-On Solution What does this product do? Kills fleas on your cat or ferret for 4 weeks. Prevents the development of flea eggs, larvae and pupae for 6 weeks when used in cats. Kills ticks on your cat for up to 2 weeks and on your ferret for up to 4 weeks. Kills biting lice on your cat.