Warm weather brings pets into contact with cat fleas. Cat flea larvae develop off the host. Adult fleas wait patiently for a warm animal to pass near enough to hop on. Once your pet has fleas, the female fleas will produce eggs that drop off your pet and develop in areas frequented by your pet including in your house. Even if you remove all the fleas from your pet, your pet can become re-infested from fleas developing into adults within your house.
In order to eliminate the re-infestation, all pets (cats and dogs) must be treated for fleas at the same time to prevent additional egg production. New fleas jumping on your pet can be controlled for up to a month with some flea products. However, the eggs from the initial infestation can produce adult fleas for 3 months. Thus, vets recommend treating all pets monthly for 3 months to eliminate the source of infestation within your home.