Fleas

Fleas are tiny wingless insects, about 1/16 to 1/8 inch long, that live by drinking the blood of mammals and birds; in US homes almost all of them are cat fleas, which feed just as happily on dogs, wildlife and people. You see the adults, but most of an infestation is hidden as eggs, larvae and cocoons in carpet, pet bedding and floor cracks, which is why fleas come back after a single spray.

This page explains how fleas live and why that matters. For the treatment plan, go to how to get rid of fleas. To check what you caught, see what fleas look like and bugs that look like fleas.

Which fleas live in US homes

• Cat flea (Ctenocephalides felis). Despite the name, it is the flea on most American dogs too, plus raccoons, opossums and feral cats. It bites people readily but cannot complete its life cycle on a human.
• Dog flea (C. canis). Uncommon in the US; mostly seen in rural kennels.
• Oriental rat flea (Xenopsylla cheopis). Lives on rats and matters because it can carry murine (flea-borne) typhus and plague.
• Human flea (Pulex irritans). Rare in modern homes; more often found on wildlife and livestock.
• Sticktight flea. Attaches in clusters around the eyes and ears of poultry, dogs and cats, mainly in the South.

For practical purposes, if you have fleas indoors you are fighting the cat flea.

How to recognize a flea

• Flattened side to side, like a sesame seed standing on edge, so it slips between hairs.
• Reddish-brown to almost black, shiny, with backward-pointing spines.
• Six legs, the hind pair long and thick for jumping. Two short antennae tucked into grooves on the head.
• No wings. Do fleas have wings? No, and they cannot fly. Anything that flies away is not a flea.
• Moves by jumping, vanishing from sight in one hop. Ticks crawl, springtails flick, fleas launch.

On a pet, look for flea dirt: black, comma-shaped specks at the base of the tail and on the belly. It is flea droppings made of digested blood.

The life cycle, and why one treatment fails

Fleas go through complete metamorphosis: egg, larva, pupa, adult.

1. Eggs. A female starts laying within 20 to 48 hours of her first blood meal and produces 20 to 50 smooth white eggs a day (Texas A&M measured about 27 a day at peak, while she drinks some 15 times her body weight in blood). The eggs are not sticky and fall off within hours wherever the pet sleeps, sits and walks. The CDC gives 1 to 10 days to hatch.
2. Larvae. Blind, white, bristly worms up to 1/4 inch long. They avoid light and burrow into carpet base, cracks and bedding, eating flea dirt, debris, eggshells and even other larvae. This stage takes about 5 to 20 days. UC IPM puts their comfort zone at 70-90°F and at least 75% relative humidity; Texas A&M says they die below 50% humidity or in soil above 95°F.
3. Pupae. The larva spins a sticky silk cocoon that gets coated with dust and fibers, so it is nearly invisible. Inside, an adult forms in about 8 to 13 days at 75°F, then waits. The cocoon shields it from insecticides.
4. Adults. They leave the cocoon when they sense vibration, warmth or carbon dioxide, which is why a house that was empty for weeks "explodes" with fleas the day you move in. Pre-emerged adults can stay put for up to 30 weeks at 52°F (CAPC) and, by UC IPM's estimate, up to a year in cool conditions. A new adult must feed within days; once on a host, it rarely leaves voluntarily.

In a warm house the whole cycle takes about 18 days to 3 weeks. At any moment, adults on the pet are roughly 5% of the population. The other 95% sits in the carpet and cocoons are largely immune to sprays, which is why every successful plan includes an insect growth regulator, daily vacuuming and a follow-up two weeks later.

How long do fleas live?

• On a host: an adult cat flea typically lives several weeks to two or three months. Grooming cuts that short: Texas A&M found fleas average about 8 days on short-haired cats and dogs, while UC IPM reports that when grooming is restricted is restricted, 85% of females are still alive at 50 days.
• How long can fleas live without a host? Texas A&M gives a few days to 2 weeks for adults off the animal. A fully formed adult still in its cocoon can wait for months.
• Larvae die quickly in dry air, direct sun and heat, which is why sunny lawns rarely hold fleas while shady, moist spots under decks do.

What do fleas eat?

Adults eat only blood. Larvae do not bite; they eat flea dirt, the blood-rich droppings of adults, plus skin flakes and organic debris. That is why the larvae are concentrated where the pet rests: the food rains down there.

Where fleas live

Indoors: the pet's bed, the carpet near favorite resting spots, under furniture cushions, along baseboards and in floorboard gaps. Outdoors: shady, humid, protected places such as under decks and porches, crawl spaces, dog houses, ground cover and leaf litter. Open lawns in full sun are poor flea habitat.

Where do fleas come from?

• Pets pick them up from other animals, yards, kennels, groomers and dog parks. Even indoor cats get fleas from people carrying adults or eggs in on shoes and clothes, or from a dog in the household.
• Wildlife. Raccoons, opossums, feral cats, squirrels and rats under the house, in the attic or crawl space are the top cause when there is no pet. Animals passing through the yard leave eggs that larvae develop from in shady spots. See opossums and raccoons.
• The previous occupant's pet. Cocoons in the carpet can wait months for the next person to walk in.

Do fleas jump, and how high?

Yes. A cat flea can jump about 8 inches high and about 13 inches forward, more than 100 times its body length. It is the reason bites concentrate on feet, ankles and shins, and the reason indoor sprays only need to cover floors, furniture undersides and the lower foot or so of walls.

What people who've had fleas say

The most common pattern in r/pestcontrol threads: someone moves into a home where the previous owner had pets, or comes back from a vacation, and gets bitten within days. Pest pros in those threads repeat three things people don't expect: a week after treatment is too early to judge (fleas keep hatching for about three weeks), vacuuming before each treatment matters because vibration wakes the cocoons, and treated pets are the best flea traps in the house. People without pets often struggle longest, sometimes for months, because nothing kills new fleas as they hatch.

Are fleas dangerous?

To people, mostly they are itchy. Flea bites are small red bumps in clusters on the lower legs; some people react strongly. Less often fleas spread disease in the US:

• Flea-borne (murine) typhus, mainly in Texas, Southern California and Hawaii, spread by cat fleas and Oriental rat fleas or their feces; linked to opossums, feral cats and rats.
• Plague, a handful of cases a year in rural parts of the Southwest, from fleas on rock squirrels, prairie dogs and other rodents.
• Cat scratch disease bacteria, which cats pick up from flea feces and pass on through scratches.
• Tapeworm (Dipylidium caninum), when a pet or a child swallows an infected flea.

For pets, fleas cause flea allergy dermatitis, tapeworms and, in kittens and puppies, anemia.

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How to prevent fleas in pets

• Keep every dog and cat in the household on a year-round, vet-recommended flea preventive, not just the one that scratches. Details for each: fleas on dogs and fleas on cats.
• Wash pet bedding every week in hot water.
• Vacuum resting areas often; it removes eggs and stimulates cocoons to hatch.
• Close off crawl spaces, porches and decks so wildlife cannot den there.
• Keep grass trimmed, avoid overwatering and clear leaf piles and debris in shady areas where pets lie outdoors. The CDC's reasoning: fleas avoid sun and need humidity.
• Store pet food in sealed containers and keep trash lids tight, so opossums, raccoons and strays don't hang around.
• Check pets regularly with a flea comb, especially in spring and early summer, when UC IPM says flea numbers rise sharply.

Getting rid of fleas: the short version

Treat the pet, the house and (if needed) the yard at the same time; use a product with an insect growth regulator indoors; vacuum daily for two weeks; repeat in 10 to 14 days. Expect to see a few newly hatched fleas for up to three weeks; they die on a treated pet. Full step-by-step plan: how to get rid of fleas in the house. Budget options and what actually works: home remedies for fleas.