Fleas: Identification, Life Cycle and Getting Rid of Them

The flea biting you or your pet is most likely the cat flea (Ctenocephalides felis). Despite the name, University of Kentucky Entomology identifies it as the most common flea on both dogs and cats. Adults are tiny, reddish brown, wingless and flattened side to side, and they jump. If you see them on a pet, find small dark specks in pet bedding, or get itchy bites around your ankles, fleas are a likely cause.

The most useful thing to know about fleas is that the adults you see are only a small part of the problem. Eggs, larvae and pupae live off the pet, in carpets, furniture and bedding. That is why fleas keep coming back when only the pet is treated, and why they can appear in a house with no pets at all.

How to identify fleas

Adult cat fleas are:

• Up to about 3 mm (1/8 inch) long
• Reddish brown to dark brown
• Wingless, with a body flattened from side to side, like a thin seed standing on edge
• Equipped with long hind legs; University of Kentucky notes they can jump up to about 6 inches straight up

On a pet, look at the base of the tail, the belly and the neck. Running a metal flea comb through the fur and tapping it onto a white paper towel is a reliable check. Tiny dark specks in the fur or bedding are likely flea feces (flea dirt), which is mostly dried blood.

Bed bugs, carpet beetle larvae and other small insects are sometimes mistaken for fleas. Fleas are the only common household biter that is flattened side to side and jumps. Our flea vs bed bug comparison and bugs in bed guide help sort out the possibilities.

The flea life cycle

Fleas go through complete metamorphosis: egg, larva, pupa and adult. Only the adult lives on the animal.

Adults

Adult cat fleas live on the host and feed heavily on blood. Mating and egg laying begin within about a day of feeding, and a female can lay roughly 20 to 50 eggs a day. University of California IPM reports that adults usually live about 30 to 40 days on a pet.

Eggs

Eggs are pearly white, oval and tiny, about 0.8 mm (1/32 inch). They drop off the pet wherever it rests, walks and sleeps: carpets, rugs, couch cushions, pet beds and your bed if the pet sleeps there. They hatch in about 2 to 5 days.

Larvae

Flea larvae are small, hairy, legless and wormlike, up to about 5 mm (3/16 inch). They live deep in carpet fibers, cushions, cracks and other protected spots. They do not bite. They feed on adult flea feces (the dried blood that falls from the pet) and other organic debris. Larvae need fairly high humidity and develop over about 8 to 15 days.

Pupae

A mature larva spins a silk cocoon, which quickly becomes coated with lint, pet hair and dust and is almost impossible to see. Inside, it turns into an adult.

This is the stage that makes fleas hard to control. The cocoon protects the developing flea from insecticides, and a fully formed adult can stay inside, waiting, for a long time. University of California IPM notes that in cool conditions fully formed fleas can remain in their cocoons for up to 12 months.

At room temperature the whole cycle from egg to adult takes about 18 days, so a few fleas on a pet can become a household problem within weeks. Flea numbers usually climb sharply in spring and early summer.

Why fleas appear after a house sits empty

A common story: someone moves into a house or comes back from a long trip, and soon their ankles are covered in bites. Here is why.

Adult fleas waiting in their cocoons emerge when they sense a host nearby. Mississippi State University Extension describes the cues as body heat, carbon dioxide in exhaled breath and, especially, vibration from movement. When the previous occupants moved out with their pets, they took the adult fleas with them but left eggs, larvae and pupae in the carpet. Those developed into adults and then sat in their cocoons with nothing to feed on. When people walk in, the vibration triggers a wave of hungry fleas that jump on the nearest warm body.

The same principle explains why vacuuming helps: the vibration coaxes waiting fleas out of their cocoons, where treatments can reach them.

Fleas in a home without pets

If you have no pets and still find fleas, look for wildlife. Raccoons, opossums, skunks or squirrels living in an attic, crawl space, chimney or under a deck can bring fleas that later find their way inside. University of Kentucky Entomology recommends having the animals removed by a wildlife control or pest professional, then treating the home. A previous occupant’s pets are the other common source.

Flea bites

Cat fleas prefer animals but will bite people, especially when their usual hosts are absent. A flea bite usually looks like a small red spot with a red halo and little swelling. It itches, sometimes intensely in sensitive people. Some people and pets develop flea bite allergic dermatitis, which can cause intense itching, reddened skin, hair loss in pets and infected skin. A single bite can set it off. A doctor or veterinarian can diagnose and treat it.

If bites become infected, or you have a rash or fever you are worried about, see a doctor.

Fleas and disease

The Centers for Disease Control and Prevention (CDC) lists these flea-borne diseases in the US:

• Flea-borne (murine) typhus, spread by infected cat fleas or Oriental rat fleas, or by their feces. Most US cases are reported from California, Texas and Hawaii.
• Cat scratch disease, usually spread through a scratch from a cat infested with cat fleas. The bacteria are shed in flea feces and get into the scratch.
• Flea-borne tapeworms, picked up when a person or pet accidentally swallows an infected flea. Young children are at higher risk, and most infected people have no symptoms.
• Plague, spread mainly by infected ground squirrel fleas. Most US cases occur in rural areas of the western states.

For most households, itchy bites and pet health are the main concerns. Keeping fleas off pets is the best way to reduce these risks.

How to get rid of fleas

Successful flea control treats the pet and the home at the same time, and keeps going long enough to catch fleas still emerging from cocoons.

Step 1: Treat every pet, with your veterinarian

Talk to your veterinarian about the right flea product for each animal. On-animal treatments such as spot-ons and oral tablets typically kill adult fleas within a day, which stops egg laying. Your vet can match the product to your pet’s species, age, weight and health.

A few important cautions:

• Treat every dog and cat in the household, not just the one that is scratching.
• Never use a dog product on a cat. Some dog flea products contain ingredients, such as permethrin, that must never be used on cats.
• Never apply carpet or yard products to pets.
• Keep pets on year-round or seasonal prevention as your vet recommends, since they can pick up fleas from kennels, groomers, other animals and wildlife.

Step 2: Clean the home

• Vacuum thoroughly all carpets, rugs, upholstered furniture, cushions, pet resting areas, along baseboards and under furniture. Vacuuming removes eggs, larvae and pupae, pulls up the carpet pile, and stimulates fleas to leave their cocoons.
• Vacuum often. University of California IPM suggests daily or every other day during an infestation. Empty the canister or seal and discard the bag outdoors.
• Wash pet bedding in hot, soapy water, and repeat at least weekly. Wash throw rugs and your own bedding if pets sleep on it.
• Vacuum hard floors too. Hardwood, tile and concrete usually do not need insecticide, but larvae hide in cracks and along edges.

Step 3: Consider a targeted home treatment

For moderate to heavy infestations, extension specialists recommend home treatments that combine an adult flea insecticide with an insect growth regulator (IGR). IGRs such as methoprene and pyriproxyfen do not kill adults; they stop eggs and larvae from developing into adults, which breaks the cycle.

Apply only products labeled for indoor flea control, follow the label exactly, focus on carpets, rugs and areas where pets rest, and keep people and pets off treated surfaces until they are dry. Total-release foggers are generally less effective than targeted sprays because the mist settles on open surfaces and misses the deep carpet and under-furniture areas where larvae live.

Step 4: Be patient and keep vacuuming

No treatment kills fleas inside their cocoons, so new adults may keep appearing for about two weeks or longer after treatment. That is normal, not a treatment failure. Keep vacuuming to stimulate emergence, and do not re-treat right away. If you are still seeing many adult fleas after about four weeks, retreatment of the home or pets may be needed.

The yard

Yard treatment is usually needed only when pets spend a lot of time outdoors. Fleas develop in shaded, sheltered spots where pets rest, such as doghouses, under decks, along fences and beside the foundation, not in open sunny lawns. A simple check is to walk through those areas wearing white socks pulled up high and look for fleas on them.

Preventing fleas

• Keep every pet on a vet-recommended flea preventive.
• Comb pets with a flea comb now and then to catch problems early.
• Wash pet bedding regularly and vacuum pet resting areas often.
• Keep wildlife out of attics, crawl spaces and the area under decks and porches.
• Before moving into a home where pets lived, have carpets thoroughly vacuumed or professionally cleaned.