Cat fleas are frequently encountered in homes and are common pests on domestic cats and dogs. Dog fleas look like cat fleas, but are rare in California. Fleas on either cats or dogs in California are most likely cat fleas.

Adult fleas are very small insects (up to 1/8 inch), so it is difficult to see a number of the characteristics used to describe them. These reddish brown to black, wingless insects are compressed from side to side so that they look like they are walking "on edge." They have piercing-sucking mouthparts through which they obtain blood meals from their hosts. Flea larvae are tiny (up to 1/16-3/16 inch), hairy, and wormlike with a distinct, brownish head, but no eyes or legs.

Female cat fleas remain on the host (unlike most other fleas) and lay about 20 to 30 eggs per day on the animal. Cat flea eggs are pearly white, oval, and about 1/32 inch long. The eggs are smooth; they readily fall from the pet and land on surfaces like bedding and carpeting in the animal’s environment. They hatch in about 2 days. The whitish, wormlike larvae feed on dried blood and excrement produced by adult fleas feeding on the pet. Larval development is normally restricted to protected places where there is at least 75% relative humidity. They feed and crawl around for 5 to 15 days at 70° to 90°F before they build small silken cocoons in which they develop into adult fleas. The cocoons are usually covered with local debris for visual camouflage. Flea larvae develop more quickly at higher temperatures. At cool temperatures, fully formed fleas may remain in their cocoons for up to 12 months. Warm temperatures and mechanical pressure, caused by walking on the carpet, vacuuming, and so on, stimulate emergence from the cocoon. At room temperatures, the entire life cycle may be completed in about 18 days. An adult cat flea generally lives about 30 to 40 days on the host; it is the only stage that feeds on blood. Fleas may be found on pets throughout the year, but numbers tend to increase dramatically during spring and early summer.

The cat flea is suspected of transmitting murine typhus to humans, but its primary importance is in its annoyance to people and pets. Cat fleas readily try to feed on almost any warm-blooded animal. Some people are bothered by the sensation of fleas walking on their skin, but bites are the major nuisance. Bites tend to be concentrated on the lower legs but can also occur on other parts of the body. The bite consists of a small, central red spot surrounded by a red halo, usually without excessive swelling. Flea bites usually cause minor itching but may become increasingly irritating to people with sensitive or reactive skin.

The best approach to managing fleas is prevention. New, safer, and more effective products aimed at controlling fleas on the pet have made flea management without pesticide sprays feasible in many situations. Management of fleas on the pet must be accompanied by regular, thorough cleaning of pet resting areas indoors and outside. Once fleas infest a home, control will require a vigilant program that includes cleaning and treating infested areas indoors, eliminating fleas on pets, and cleaning up and possibly treating shaded outdoor locations where pets rest.

On the Pet
Several types of products are available to control fleas on dogs and cats. The most effective and safest products inhibit normal growth or reproduction of fleas. Use of these products must be supplemented with good housekeeping in areas where the pet rests. Contact your veterinarian for advice and assistance in selecting the best flea control product for your situation.

Preferred On-pet Flea Treatment Products. New product innovations have made it possible to effectively, conveniently, and safely prevent flea populations from building up on pets. These products are more effective and safer than the traditional insecticide dusts and sprays, which until a few years ago were the only choice for pet owners. The new products contain insect growth regulators (IGRs) such as methoprene (Precor) or pyriproxyfen (Nylar), and insect development inhibitors (IDIs) such as lufenuron (Program). The IGRs are available as flea collars or spot-ons applied to one or two places on the pet’s coat. IDIs come formulated as a systemic treatment that must be administered orally and are available from veterinarians. These products work by either preventing the larvae from turning into adults (IGRs), or the eggs from hatching (IDIs), and are virtually nontoxic to pets and people. Two other new types of safe and effective chemicals are fipronil and imidacloprid, which are used as spot-ons. If properly applied before flea season begins and reapplied as necessary, any of these products can prevent a flea infestation.

Spot-on Formulations. Imidacloprid (Advantage) and fipronil (Front-Line) are available from veterinarians and are applied to the animal’s coat; a single application provides flea control for 1 to 3 months. These spray and spot-on formulations are much easier to use than baths and are more acceptable to the animal. Both products are available as spot-ons; a few drops applied to the animal’s shoulder blades move through the animal’s coat, providing whole-body treatment. Both materials kill adult fleas within hours of the flea jumping on the animal. Also, these compounds have lower mammalian toxicity than traditionally used flea control products such as carbamates and organophosphates and are safer to use on pets. Generally the spot-on formulations can withstand bathing; check the label for specific instructions.

Systemic Oral Treatments. Several flea control products are internal medications that are administered on a regular basis in the form of a pill or food additive. Older types of medications contained insecticidal materials, mostly organophosphates, that were transported to all skin areas through the animal's blood. Newer products contain insect development inhibitors that do not have the toxicity of the older materials and are much safer to use. The insect development inhibitor lufenuron (Program) can be given as a pill (dogs) or as a food additive (cats) once a month to suppress flea populations. It can also be administered as an injection every 6 months. While this compound does not kill adult fleas, it does prevent flea reproduction. If its use is initiated early in the year before flea populations begin to build, it can prevent the establishment of a flea population in the home, though an occasional adult flea may be sighted on the animal.

Flea Collars. Flea collars containing the insect growth regulators methoprene and pyriproxyfen are virtually nontoxic to pets and humans and can be used on both cats and dogs. The growth regulator is released by the collar and distributed throughout the fur of the pet. Adult fleas coming in contact with the growth regulator absorb it into their bodies where it accumulates in their reproductive organs. Eggs laid by the adult female do not hatch. Flea collars may contain the insect growth regulator as the sole active ingredient or it may be combined with an insecticide. If the collar contains only the insect growth regulator, use another treatment, such as a spot-on product, to control adult fleas if necessary. Flea collars containing methoprene are effective for 4 to 6 months on a dog and up to a year on cats.

Sanitation. Thoroughly and regularly clean areas where adult fleas, flea larvae, and flea eggs are found. Vacuum floors, rugs, carpets, upholstered furniture, and crevices around baseboards and cabinets daily or every other day to remove flea eggs, larvae, adults, and food sources. Vacuuming is very effective in picking up adults and stimulating preemerged adults to leave their cocoons, but it is not as good at removing flea pupae because they are attached to carpet fibers and can withstand the pull of the vacuum. Flea eggs can survive and develop inside vacuum bags and adults may be able to escape to the outside, so immediately destroy bags by burning or by sealing them in a plastic trash bag and placing them in a covered trash container. Launder pet bedding in hot, soapy water at least once a week.

Insecticides. Several insecticides are registered for controlling fleas indoors. Sprays are only needed when you detect an infestation in your home. The most effective products contain one of the insect growth regulators: methoprene or pyriproxyfen. Fleas are known to build up resistance to insecticides, so always supplement sprays with other methods of control such as thorough, frequent vacuuming.