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G7380, Fleas

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Revised by Richard M. Houseman
Division of Plant Sciences

Fleas are blood-sucking ectoparasites of humans and domestic animals all over the world. More than 2,200 species of fleas have been identified worldwide, but only about 30 species are found in Missouri. Humans are affected by very few of these species. The most common species in Missouri is the cat flea, Ctenocephalides felis (Figure 1), but we also occasionally encounter the dog flea, Ctenocephalides canis, the human flea, Pulex irritans, and the oriental rat flea Xenopsylla cheopis. An understanding of flea control is important because of their worldwide distribution, abundance, irritating bite and ability to transmit diseases.

Cat flea Figure 1
The cat flea, Ctenocephalides felis.

Flea bites

The mouthparts of adult fleas are adapted for puncturing animal skin and sucking blood. Both male and female fleas suck blood. Fleas normally prefer the blood of pets over that of humans, so it is not unusual for people to coexist with their pet and its flea population under normal conditions and be bitten only occasionally. However, when the preferred host is removed from the environment, such as during vacation, a population of hungry adult fleas will accumulate. Hungry fleas lose their preference for pet blood and will attack almost any warm-blooded animal that comes near.

Cats and dogs scratch and bite themselves constantly when heavily infested. As a result, their skin is irritated and their coats become soiled and roughened. The initial irritation, itching, and rash are caused by salivary secretions that the flea injects during feeding.

Human reactions to fleabites vary from person to person. A typical human reaction is a small, hard, red, itchy spot. Fleas are apparently not attracted to some people, while other people are highly susceptible. Additionally, in flea-infested households, some may experience severe irritation from fleabites, while others show no signs.

Fleas bite people most often on the legs and ankles. They typically make two or three bites in a row. A small red spot with a light-colored center appears where the mouthparts entered the skin. There is normally no swelling. Some bleeding may occur, especially if the bite is scratched. A single puncture point caused by the mouthparts is generally apparent in the center of each spot. This characteristic distinguishes fleabites from the bites and stings of other arthropods. Spiders leave two marks when they bite, and the bites of mosquitoes, bees, wasps, and bedbugs normally produce a large swelling or welt.

Life cycle

Four stages make up the life cycle of fleas: egg, larva, pupa and adult.

Under normal conditions, the entire life cycle of cat fleas may be completed in as little as 20 to 35 days (Figure 2). The cycle is influenced by temperature and moisture conditions. Ideal conditions are 85 degrees Fahrenheit and 85 percent relative humidity. Under less favorable conditions, development takes longer and may require several months or even a year. Sustained temperatures below 55 degrees Fahrenheit inhibit development. Flea reproduction takes place indoors year-round, but outdoor reproduction is limited to warm-weather months.

Fleas life cycle Figure 2
Typical flea life cycle (20 to 35 days).

Flea eggs are smooth, oval, whitish and about 1/50 inch long. The fertilized adult female flea lays 2 to 14 eggs after each blood meal and up to 800 eggs during her lifetime. They are usually deposited onto the skin or hair of the host pet. These eggs drop off during a pet's normal activities onto bedding, carpet, rugs, mats, etc. The greatest concentration of eggs is usually where the pet spends the greatest amount of time.

Flea eggs hatch into larvae in 2 to 14 days, depending on environmental conditions. Newly hatched larvae are about 1/16 inch long and will grow to a length of 1/4 inch. They grow by molting, or periodically shedding their skin. They pass through three molts and are fully developed in 8 to 24 days. Larval growth can be prolonged to more than six months under adverse conditions.

Flea larvae live in floor cracks, rugs, carpets and animal bedding. They are legless but move with the aid of bristles on their body. Larvae prefer dark, moist environments where they feed on a wide variety of organic debris. Food items include dry feces from adult fleas, pet feces, and particles of pet food.

Before entering the inactive pupal stage, a fully grown flea larva spins a silk cocoon. It incorporates debris particles into the cocoon as it is spun. The debris helps camouflage the cocoon within its surroundings. The larva pupates inside the cocoon, gradually darkening to a brownish color. It remains in the pupal state 5 to 7 days, but this stage may last for up to a year in unfavorable conditions.

Adult fleas are small, wingless insects approximately 1/12 to 1/8 inch long. They are dark reddish-brown to black. The last pair of legs is modified for jumping and an adult flea can jump up to 8 inches vertically and 16 inches horizontally. Their bodies are thin (laterally compressed) and covered with stout, backwardly directed spines, which allow fleas to move forward through the hair or feathers of the host while also helping them to resist being pulled out during grooming.

Adult fleas remain in the cocoon until a suitable host is detected. Depending on environmental conditions, an adult flea can remain in the cocoon for up to five months waiting for a host. From inside the cocoon, adult fleas recognize the presence of a potential host by sensing body heat, odor, air movement or vibration of floors and surroundings. Once suitable stimuli are detected, the adult flea exits the cocoon and seeks out the host. This behavior is one reason flea infestations are often discovered by people returning home after vacation or moving into a new home or apartment where hungry adult fleas have been waiting for an extended period of time inside a cocoon without access to available hosts.

Medical importance

Several pathogens may be transmitted by the bite of adult fleas. Plague (black death) and typhus continue to be a threat to human populations in the United States. Plague is found in some western states. Rodent populations serve as the reservoir for plague-causing organisms, and several flea species vector the disease to humans. Typhus occasionally occurs in the southwestern and Gulf Coast states. This disease is transmitted from rats to humans by the oriental rat flea (Xenopsylla cheopis).

Various tapeworms are transmitted by the cat (Ctenocephalides felis) and dog (Ctenocephalides canis) flea. Many cats and dogs are infected with the tapeworm Dipylidium caninum. This tapeworm is transmitted when your pet ingests an adult flea infected with the larval tapeworm. Once inside the pet, the adult tapeworm develops and begins to produce eggs, which are shed in the pet's feces. Young children are infected when they are in close contact with pets and inadvertently swallow an infected adult flea.

Rodents and pets are the most common sources of fleas and the diseases they vector. Flea feeding behavior and their lack of host specificity increase the potential for fleas to transmit disease-causing organisms between humans and their companion animals. An increased risk for flea bites and disease transmission from animals to humans exists in environments such as urban/rural interfaces, parks and natural areas.


Flea control is a complicated problem. This is because there are multiple stages in the flea life cycle, and these stages are found on and off the pet both inside and outside the home. Flea control strategies have to consider all of the growth stages and where they are located. Treating for only one or two stages or locations almost always leads to reinfestation, because any growth stage that is not eliminated will eventually find hosts and become redistributed. Despite these challenges, you can solve flea problems by first directing control strategies at flea stages on infested pets, and then focusing on the places these pets spend their time.

Because pets are the primary sources of flea infestations, attention should be given to pets and pet activities first. Whenever possible, establish one sleeping area for your pet that can be cleaned easily and regularly. Don't allow a pet in areas of the home where fleas are particularly annoying or where cleaning is difficult. Regularly wash all bedding, rugs, etc., to which a pet has frequent access. When grooming a pet, use a flea comb, and bathe pets regularly. Soaps are very effective at killing fleas, especially when left on for 5 to 10 minutes before rinsing. However, you only kill the fleas on the animal, so reinfestation is likely unless you also treat places where your pet spends time.

Veterinarians are able to provide flea control recommendations for your pet, and some of the best flea control products are available for purchase only through a veterinarian. These products are usually formulated to be absorbed into the bloodstream of the pet and kill adult fleas that take a blood meal. They may also contain an ingredient that disrupts the reproduction of female fleas or the growth and development of immature flea stages.

Approved over-the-counter insecticides can be purchased for direct application to your pet. Flea control products come in a variety of formulations including oils, dips, dusts, sprays and shampoos. They vary in their cost and effectiveness. If you choose to treat your pet without the advice of a veterinarian, always use flea control products according to instructions on the label. Dust formulations are often more effective than sprays. When using dusts, put on rubber gloves, use a shaker, and rub the dust into the hair, being particularly thorough around the ears, between the legs and around the tail. Be sure to keep the dust out of the animal's eyes, nostrils and mouth. Flea collars are of some value in preventing an infestation from getting established but are of practically no value in eliminating an existing one.

Because flea development occurs off of the host, attention must also be given to the areas in which pets are active. Remember that flea eggs fall off of the hosts as they move around their environment, and these eggs hatch into larvae that eventually develop into new adult fleas that reinfest your pet.

Vigorously vacuum the entire house--especially areas visited frequently by pets. Although vacuuming will not remove all fleas or all life stages, you should vacuum regularly (weekly) and thoroughly to remove as many fleas as possible. Areas that require special attention include pet resting areas, carpets (particularly around legs of furniture that pets rub against), cracks and crevices along baseboards, upholstered furniture (if the pets are allowed on such furniture), and under beds if the pets are allowed on the beds. As soon as vacuuming is completed, remove the vacuum bag and put it in a sealed plastic bag and place in the trash. If the vacuum bag is not removed, it can become a source of reinfestation inside the home.

If a flea infestation is minor, frequent and thorough vacuuming might solve the problem. However, heavy infestations usually require an accompanying application of an insecticide spray to carpeting, cracks and crevices, or other areas where fleas are present. Several over-the-counter insecticides with varying effectiveness can be purchased for this purpose. Products containing pyrethrins or synergized pyrethroids (active ingredients usually have the suffix — thrin) are the most common. Good results have been achieved using these products along with a product containing an insect growth regulator (active ingredients are methoprene or fenoxycarb). These products are odorless and nonstaining.

When using spray treatments, it is usually necessary to make a second application 10 to 14 days following the first. This is necessary because eggs and pupae are more resistant and may not have been affected by the initial treatment. By the second application, eggs and pupae will have developed into larvae and adults, which are more susceptible to spray treatments.

A pest management company can apply spray treatments if you do not want to do it yourself. If you choose to hire a pest management professional, you should obtain estimates from two or three companies and understand exactly what services you will receive. Normally, they will recommend a thorough cleaning of carpets, bedding areas, etc. before they treat these areas with a spray treatment. They will not treat animals, so you will still be responsible for the fleas on your pets.

Total release aerosols (bombs) containing pyrethrins or pyrethroids are available for killing adult fleas. Although effective on adults, this type of application does not affect the other life stages, and reinfestation is likely unless treatment incorporates other strategies.

Warning on the use of chemicals

Apply chemicals only where needed or justified. Before using any chemical, read the label carefully for directions on application procedures, appropriate rate, first aid, storage and disposal. Make sure that the chemical is properly registered for use on the intended pest and follow all other label directions. Keep insecticides in original containers, complete with labels, and keep them out of the reach of children and pets. Do not allow children or pets near treated areas before these areas dry. Carefully and properly dispose of unused portions of diluted sprays and empty insecticide containers.

G7380 Fleas | University of Missouri Extension