Life Cycle of the Flea

Getting rid of fleas on your pet takes a few treatments

Colored SEM side view of a cat flea. x 50 The strong rear jumping legs can be seen as well as the eyes, and biting mouthparts.
Clouds Hill Imaging Ltd. / Getty Images

Fleas. They make pets' lives miserable, and humans begin to itch just at the thought of them. Vets are often asked what pill, drug, dip, collar, or shampoo works the best to get rid of these persistent parasites. The answer is there is no single method or insecticide that will completely eradicate (or at least control) a flea problem.

What are Fleas?

There are many hundreds of species of fleas. Collectively, all of the species of fleas are categorized under the order name of Siphonaptera. The cat flea, Ctenocephalides felix, is the most commonly found flea in the US and infests cats, dogs, humans, and other mammalian and avian hosts.

Fleas thrive in warm, moist environments and climates. Fleas subsist on blood from the host animal; dog, cat, human and so on. Ninety-five percent of flea hosts are mammals, the other 5 percent are bird species.

Flea saliva, like other biting skin parasites, contains an ingredient that softens, or "digests" the host's skin for easier penetration and feeding. The saliva of fleas is irritating and allergenic and the cause of all the itching, scratching, and other signs seen with flea allergy dermatitis.

Fleas have four main stages in their life cycles: egg, larva, pupa and adult. The total flea life cycle can range from a couple weeks to several months, depending on environmental conditions.

Adult Fleas

The adult flea has a very flat body. There are hair-like bristles on the flea's body and legs to aid navigation through pet hair. Fleas have three pairs of legs, the hindmost pair designed for their well-known jumping ability.

Adult fleas prefer to live on the animal and their diet consists of blood meals courtesy of the host animal. The female flea lays white, roundish eggs. The adult female flea can lay up to 50 eggs per day, and 500 to 600 eggs over several months.

Flea Eggs

The eggs are not sticky (like some parasites), and they usually fall off of the animal into carpet, bedding, floorboards and soil. The timing of when the flea egg hatches varies—anywhere from two days to a few weeks, depending on environmental conditions.

The larva emerges from the egg using a chitin tooth, a hard spine on the top of the head that disappears as the flea matures.

Flea Larvae

The larval stage actually has three developmental stages during this stage. Larvae are about 1/4 of an inch long, and are a semi-transparent white. They have small hairs along their bodies and actively move.

They eat the feces of adult fleas (which is mostly dried blood) and other organic debris found in carpet, bedding and soil. Depending on the amount of food present and the environmental conditions, the larval stage lasts about 5 to 18 days (longer in some cases) then the larva spins a silken cocoon and pupates.

Flea Pupae

The pupa is the final developmental stage of the flea before it becomes an adult. The adult flea can emerge from the cocoon as early as 3 to 5 days, or it can stay in the cocoon for a year or more, waiting for the right time to emerge.

Stimuli such as warm ambient temperatures, high humidity, even the vibrations and carbon dioxide emitted from a passing animal will cause the flea to emerge from the cocoon faster. This brings us back to the adult flea.

The entire life cycle is quite variable, as evidenced by the variability in each life stage progression. As mentioned above, the cycle can be as short as two weeks or as long as two years. That is why it is so important to remain vigilant, even when a flea problem is thought to be under control. The duration of flea season varies by location.

Flea Control on Your Pet

This is where most pet owners focus first—getting those fleas off of the beloved pet. The constant scratching, biting, and licking are bothersome on their own, and it is not healthy for the animal's skin, either. Flea allergy dermatitis is a common reason for veterinary visits all year-round in some areas.

Treatments for pets infected with fleas include:

  • Shampoos: A shampoo, or "flea bath" is a good first attack on fleas for the pet that has large numbers of fleas visible on its body. A flea shampoo is not intended for lasting control, usually only effective for a day or less. They leave little residual chemical on the animal when properly used.
  • Dips: These strong chemical rinses rid animals not only of fleas but mites and ticks as well, and last about two weeks. They're only effective at getting rid of adult fleas.
  • Collars: The best flea collars absorb into the animal's subcutaneous fat layer. While most are effective for adult fleas, some can prevent egg and larval development as well.
  • Spot-on treatments: These products are applied between the shoulder blades of the pet and typically last about one month. Effective for adult fleas, some also will inhibit larval development.
  • Pills: oral or injectable medications stop the larva from emerging from the flea egg, and help break the life cycle when used in tandem with an adulticide treatment.