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How to identify it
- Adults are reddish brown to nearly black, wingless and no more than about 1/8 inch long, with strong jumping legs.[1][7]
- The body is flattened side to side, so fleas look as if they are walking on edge.[1]
- Flea droppings (digested blood) show up as dark, pepper-like specks in the pet's fur.[6]
- Larvae are up to 3/16 inch long, hairy and wormlike, with a brownish head and no eyes or legs.[1][7]
- UC IPM describes a flea bite as a small red spot with a red halo, usually without much swelling.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Dog flea | Looks like the cat flea but is rare in California; fleas on pets there are most likely cat fleas, and CDC lists both among the few fleas that affect people's health.[1][4] |
| Sticktight flea | Females attach firmly along the ears and eyes of the host instead of moving through the coat; common on ground squirrels and poultry and a problem with pets that roam.[1] |
Where it lives
Adult cat fleas stay on the host; eggs, larvae and pupae develop where pets rest, especially bedding, carpets and shaded outdoor spots such as kennels, crawl spaces and areas beneath decks. Larvae need protected spots with at least 75% relative humidity and do poorly in sun or heavy foot traffic.[1]
Biology and life cycle
Adults feed, mate and lay eggs on the host. UC IPM says females lay about 20 to 50 eggs a day; Kentucky says 40 to 50, with mating and egg laying starting within 24 hours of a flea jumping onto the pet. The smooth eggs fall off into bedding and carpet and hatch in about 2 to 5 days.[1][6]
Larvae hide at the base of carpet fibers and under cushions and feed for 8 to 15 days on the dried blood and droppings adult fleas leave behind, then spin silken cocoons covered in debris.[1][6][7]
Warmth and pressure from footsteps or vacuuming trigger adults to emerge. At room temperature the whole life cycle can take about 18 days, and an adult cat flea usually lives about 30 to 40 days on the host.[1]
Adults jump up to about 6 inches high, so they easily ride onto passing pets or people's shoes and pant legs; they seldom jump directly from one pet to another. Pets also pick them up at kennels and groomers or from strays and wildlife such as opossums and raccoons.[6]
People may be bitten, especially when flea numbers are high, but cat fleas do not live and reproduce on people. Numbers usually rise sharply in spring and early summer, when conditions favor larvae.[7][1]
Damage and signs
Health risk
CDC says flea bites can cause itching and irritation, and that fleas sometimes infect people or pets with germs that cause flea-borne typhus, plague or cat scratch disease. Flea allergy dermatitis is the most common skin disease of small pets. Dogs, cats and people (most reported human cases are children) get dog and cat tapeworm by swallowing an infected flea. Cat fleas are also the main carrier of Rickettsia felis, the cause of flea-borne spotted fever.[4][8][5][9]
Control
Prevention
Treat every pet with a veterinarian-recommended spot-on or oral flea product; these kill fleas within hours of their jumping aboard and work better than collars, dusts, shampoos and sprays. Starting early in the year, or keeping pets on a preventive schedule, stops fleas from establishing in the home. Never use permethrin or amitraz products on cats.[1][6][7]
Sanitation
Vacuum floors, rugs, upholstered furniture and crevices daily or every other day, including under furniture and cushions and along walls, and wash pet bedding in hot, soapy water at least once a week. Texas A&M found a beater-type vacuum removes 15 to 30 percent of larvae and 30 to 60 percent of eggs from carpet. Seal and discard the bag outdoors, since fleas can keep developing inside it.[1][6][7]
Traps and physical control
A metal flea comb removes adult fleas and shows whether other measures are needed; dip it in soapy water or alcohol to kill the fleas you comb out.[1][7]
Pesticides
Indoors, the most effective flea sprays pair an adult-killing insecticide with an insect growth regulator such as methoprene or pyriproxyfen; spray carpets, pet sleeping areas and under furniture directly. Hardwood, tile and concrete floors usually need only vacuuming.[1][6]
Expect new fleas to keep emerging for about 2 weeks after spraying, because sprays don't kill pupae in their cocoons; keep vacuuming instead of re-treating right away.[1][6][7]
Outdoors, spraying is seldom needed if pets are treated. If it is, treat only where pets rest, such as kennels, under decks and along the foundation; open, sunny lawn is unlikely to hold many fleas.[1][6][7]
Diseases fleas can spread to people
Flea-borne (murine) typhus spreads to people through infected fleas, most often the Oriental rat flea and the cat flea, which pick it up from animals such as rats, cats or opossums. Most U.S. cases are reported from southern California, Hawaii and southern Texas; symptoms include fever, chills, aches and headache, and about half of patients get a rash.[2][4]
Cat scratch disease spreads when a cat's scratch is contaminated with flea feces; kittens and stray cats are more likely to carry the bacteria. CDC advice includes veterinarian-approved flea control, keeping cats indoors, and washing scratches with soap and water.[3][4]
Dog and cat tapeworm segments look like grains of rice near a pet's anus or in fresh stool. CDC calls flea control the most effective way to prevent infection in pets and people, and says children should wash their hands after playing with pets.[5]
CDC's typhus prevention steps: keep fleas off pets, keep rodents and wild animals such as opossums away from the home, and protect yourself from flea bites with EPA-registered repellents.[2]
Where sources disagree
Eggs: UC IPM gives about 20 to 50 eggs a day per female; Kentucky gives 40 to 50.[1][6]
Time in the cocoon: UC IPM says fully formed fleas can wait in the cocoon up to 12 months at cool temperatures; Kentucky gives 1 to 4 weeks, longer when conditions are unfavorable such as a vacant home, and Texas A&M says the pupal stage normally lasts 7 to 14 days.[1][6][7]
Foggers: UC IPM says total-release foggers lack the coverage of direct sprays unless they contain methoprene or pyriproxyfen; Kentucky does not recommend foggers for fleas at all.[1][6]
Re-treating: UC IPM says not to treat again for at least several weeks; Kentucky says retreatment may be needed if adults are still seen after 4 weeks, and Texas A&M says follow-up treatments are usually needed with short-lived botanical sprays.[1][6][7]
Common questions
- Why do I still see fleas after treating?
- Sprays don't kill pupae in their cocoons, so new adults keep emerging for a couple of weeks or more; keep vacuuming to draw them out, and keep pets treated so emerging fleas die.[1][6]
- How can I tell if my yard has fleas?
- Walk around pet resting areas wearing white socks pulled up to the knee; fleas will jump on and be easy to see.[1][6]
- Do brewer's yeast or ultrasonic collars repel fleas?
- No. Studies show neither vitamin B1 nor brewer's yeast prevents flea feeding, and herbal collars and ultrasonic devices aren't effective repellents.[1][7]
- Can fleas make my pet sick?
- Yes. Flea allergy dermatitis is the most common skin disease of small pets, and pets get tapeworms by swallowing infected fleas while grooming.[8][5]
- Can I get fleas without a pet?
- Yes. Raccoons, opossums, skunks, squirrels or feral cats living in an attic, chimney or crawl space can bring fleas into the home; have the animals removed, then treat.[6]
Sources
- University of California Statewide IPM Program, “Pest Notes: Fleas, Publication 7419 (September 2010).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnfleas.pdf (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “About Flea-borne Typhus (updated December 11, 2025).” www.cdc.gov/typhus/about/murine.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “About Cat Scratch Disease (reviewed September 11, 2026).” www.cdc.gov/bartonella/about/about-cat-scratch-disease.html (accessed 2026-11-11)
- Centers for Disease Control and Prevention, “About Fleas (updated November 2, 2026).” www.cdc.gov/fleas/about/index.html (accessed 2026-11-11)
- Centers for Disease Control and Prevention, “About Dog or Cat Tapeworm Infection.” www.cdc.gov/dipylidium/about/index.html (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-602: Flea Control and Prevention (revised March 2026).” entomology.mgcafe.uky.edu/ef602 (accessed 2026-11-11)
- Texas A&M AgriLife Extension, “Flea Control in and around the Home (ENT-3001).” citybugs.tamu.edu/factsheets/biting-stinging/others/ent-3001/ (accessed 2026-11-11)
- Compendium: Continuing Education for Veterinarians, via PubMed, “Lam and Yu (2009), Overview of flea allergy dermatitis.” pubmed.ncbi.nlm.nih.gov/19517416/ (accessed 2026-11-11)
- Current Tropical Medicine Reports, via PubMed, “Brown and Macaluso (2016), Rickettsia felis, an emerging flea-borne rickettsiosis.” pubmed.ncbi.nlm.nih.gov/27340613/ (accessed 2026-11-11)
- iNaturalist, “Ctenocephalides felis taxon page (order and family).” www.inaturalist.org/taxa/311218 (accessed 2026-11-11)