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1/4 inch in length

Distinguishing Marks

Laterally flattened
Brown to black or gray in color
Wingless and have long hind legs for jumping

Behavior and Ecology

Each species of flea has one or two kinds of animals it prefers, although when hungry, it will attack a wide variety of warm-blooded animals, sometimes including humans. Adult fleas live on the blood of the animals, and must have a blood meal to reproduce. Cat fleas (Ctenocephalides felis), and dog fleas (Ctenocephalides canis) are the species most often found in houses. Cat and dog fleas periodically jump on and off the host. When the host is removed for a period of time,

they are left without food. Hungry adult fleas often attack on the first warm-blooded animal that comes in the door, often biting people around the ankles. In addition, vibrations are known to promote emergence of new adults from pupae; walking across the floor may trigger emergence.


Female fleas lay eggs, usually on the host. However, the eggs are not attached to the host, and soon fall off and develop on the ground or in the host's nest or resting place. The eggs hatch in 2 to 12 days under favorable conditions (65-80 degrees F, and at least 70% relative humidity). The young larvae are tiny, whitish, and legless, with bristly hairs. They have a well-developed head capsule with chewing mouthparts. Flea larvae feed on organic debris (hair and shed skin of the animal), their own cast skins, and on the feces of adult fleas. Thus they are often found in pet resting places. Larvae tend to avoid light by burrowing down into carpeting, or hiding under pet bedding. The larval stage may last from 4 to 24 days in the summertime, 21 to 200 days under

less favorable conditions. When fully grown, the larva spins a silken cocoon and enters the pupal or resting stage. The pupal stage usually lasts 5 to 14 days, but if the stimuli for emergence are absent, fleas may remain in the pupal stage for prolonged periods of time. The adult cat and dog fleas emerge from the pupae, and often crawl up on blades of grass outdoors, or onto furniture, draperies or the like indoors, and wait for a host to pass. They jump quickly onto the host and begin feeding. Adults of the cat flea and dog flea are long-lived; they may live for a year or more, with periodic feeding.


Fleas have sucking mouthparts, and as adults, feed on the blood of mammals or birds. Many species are very annoying because of their bites, and a few act as vectors for disease. Some people and pets are known to develop allergic reactions to flea bites. Fleas become pests when they get into our houses. Fleas in houses are usually linked with a pet or a visiting cat or dog. Wild animals have fleas also, and if such animals are living in the homes, fleas may become a problem. Flea problems often occur when the host animal has been absent for a period of time, such as when the family goes on vacation, taking or boarding the pet. Fleas may also be driven into the house during prolonged periods of wet weather.
Cornell University, Dept. of Entomology, 2144 Comstock Hall, Ithaca NY 14853-2601
Prepared 1972 by Carolyn Klass, Senior Extension Associate, Dept. of Entomology, Cornell University
Updated 2012

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