The Life Cycle of the Flea

Understand Fleas so You Can Get Rid of Them on Your Pet and in Your House

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.

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. The main flea food is blood from the host animal. Host animals are many species—cats, dogs, humans, etc. Fleas primarily utilize mammalian hosts (about 95%). Fleas can also infest avian species (about 5%). 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, or FAD.

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


The adult flea is very flat side to side. There are hair-like bristles on the flea body and legs to aid in their navigation through pet hair. Fleas have 3 pairs of legs, the hindmost pair designed for jumping. Fleas are well known for their jumping abilities.

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, 500-600 eggs over several months.


The eggs are not sticky (like some parasites), and they usually fall off of the animal into the carpet, bedding, floorboards, and soil. 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.


(plural = larvae)

The larval stage actually has three developmental stages during this stage. Larvae are about 1/4" (6.35 mm) long, and semi-transparent white. They have small hairs along their body and actively move. They eat the feces of adult fleas (which is mostly dried blood) and other organic debris found in the 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.


(plural = pupae)

The pupa is the last stage before 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. When is the right time? (Never, say pet lovers everywhere!) 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 with 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, or FAD, is a common reason for veterinary visits all year-round in some areas.

A mistake seen all too often is the "more is better" approach that some people take. More is NOT better when it comes to chemicals or medications. Following package directions is essential when using over the counter products and medications. Only buy products that are labeled for use on the species you will be using them on (dog, cat, etc.). Cats, in particular, are very sensitive to drugs and chemicals—be sure to read all labels carefully.

Even when labels are read and instructions are followed, adverse reactions to flea product can happen. Call your vet immediately. Other resources are animal poison control center and adverse drug reporting hotlines.

Shampoos and Dips

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. Cats can be difficult to bathe. It is important to know how to properly use the medicated shampoo to effectively rid your pet of fleas. It is also important to realize that a flea shampoo is not intended for lasting control. Many people are surprised when they see fleas and it was "only a week ago" that the pet had a flea bath. Shampoos are only effective for a day or less. They leave little residual chemical on the animal when properly used.

Flea dips are strong chemical rinses to rid animals not only of fleas but mites and ticks as well. I do not recommend dips unless absolutely necessary, as in the case of a mite infestation. Dips last approximately 1 to 2 weeks. That is a lot of chemical residue to leave on an animal. Flea shampoos and dips are effective for adult fleas.

Flea Collars

Flea collars work one of two ways—by emitting a toxic (to fleas, anyway) gas, and by being absorbed into the animal's subcutaneous fat layer. The toxic gas is usually only effective in the immediate area of the head and neck. This type of collar is best used in the vacuum cleaner bags to kill any fleas vacuumed up. The collars that absorb into the subcutaneous fat are much more effective. Ask your vet what collars they carry. Collars are not for all pets—particularly cats that roam outside.

Flea collars are effective for adult fleas. Some collars have an IGR, or Insect Growth Regulator, to prevent flea egg and flea larval development as well.

Flea Powders and Sprays

Flea powders and sprays offer short-term (2 to 3 day) protection from fleas, and with some products, ticks, and mites too. Powders and sprays have fallen out of favor recently with the newer spot-on treatments that are available.

Most flea powders and sprays are only effective for adult fleas, some offer additional flea protection by inhibiting flea egg and larval development (contain an IGR).

Spot-on Treatments

Common brand names include: Advantagetm, Frontline, and Bio-Spot just to name a few. These products are applied between the shoulder blades of the pet and typically last about one month.

Spot-on treatments are effective for adult fleas. Some include ingredients to inhibit the larva from emerging from the flea egg and some are active against larval development as well.

Oral medications

Flea "pills" work by stopping the larva from emerging from the flea egg. Program is also available as an injectable medication for cats. Fleas ingest the blood of animals on these medications, and the female fleas then lay eggs that are unable to hatch. They do NOT kill adult fleas. These medications are essential to break the flea life cycle and stop the flea problem when used in conjunction with flea adulticide treatments.

Flea Control for Your House and Yard

Flea control doesn't stop after your pet has been taken care of! Only about 10% of the flea population (mainly the adults) are on your pet. The flea eggs, larvae, pupa, and the few adults that reside in the carpeting, bedding, and living areas make up approximately 90% of the flea population. Neglecting this population of fleas will ensure that the flea problem will continue and worsen over time.


  • Daily vacuuming - this is very important for picking up adults, eggs, larvae, and pupae before they develop. Putting a flea collar in the vacuum bag and emptying the bag frequently are also important; otherwise, the fleas will hatch, develop, and leave the vacuum to re-infest the living quarters. See: Sharing a ha
  • Wash all bedding, clothing, and removable furniture covers.
  • Apply insecticide - over the counter fogger or by a professional exterminator, such as Orkin. Follow all instructions very carefully, remove all pets, people, and cover all food in the environment before applying insecticide and make sure everything is dry and it is safe to return according to package directions. Take special precautions for pets and children—eating or putting items in their mouth, etc.