Why do I still have fleas after treating my pet?

The most likely reason is that the treatment is working and the fleas you see are new ones hatching from the house. Even after the pet and the home are treated, expect to see some fleas for a few weeks or longer.^[1] If it has been longer than that, one of a handful of other causes is usually to blame, and each has a fix.

Reason 1: the house is still full of developing fleas

Adult fleas lay their eggs in the pet's fur, 40 to 50 a day, and the eggs soon fall off into carpet, under furniture cushions and wherever the pet rests or sleeps.^[1] The larvae hide under carpet fibers and cushions, feeding mainly on the dried blood adult fleas leave behind, then spin silk cocoons covered in bits of debris.^[1] At normal room temperatures, the whole cycle from egg to adult can take about 18 days.^[2] So on the day you treat your pet, there may be weeks of fleas already in the pipeline.

The cocoons are the stubborn part. Pupae stay in the cocoon for 1 to 4 weeks, and longer when conditions are poor, for example when an infested home sits empty.^[1] At cool temperatures, fully formed fleas can stay in their cocoons for up to 12 months, and warmth and the pressure of walking or vacuuming on carpet trigger them to emerge.^[2] That is why a house that sat vacant can erupt in fleas a few days after a family moves in. The cocoon is impervious to insecticides, another reason fleas can persist after the pet and home are treated.^[1]

The fix: time and vacuuming. Daily vacuuming is the best first step for a flea infestation, because it removes eggs, larvae and adults.^[4] Vacuuming also stimulates fleas to emerge sooner from their cocoons, bringing them into contact with the treatment.^[1] Keep going rather than respraying. If adult fleas are still showing up after 4 weeks, the house, the pets or both may need treating again.^[1]

Reason 2: not every pet is treated

A treated pet ends an infestation only as long as all pets remain treated.^[1] An outdoor cat, a second dog that hates pills, or a pet that was skipped this month keeps laying eggs in the house. Treating only the scratching pet does nothing for the one that is quietly carrying the colony.

The fix: treat every dog and cat in the home, on schedule, with a product meant for that animal.

Reason 3: the product, the dose or the schedule is off

• Wrong animal or weight. Use products only on the species and the size or weight the label names; products are designed for specific weights.^[5] Using a product made for a larger animal can overexpose a smaller pet to the pesticide.^[5]
• Wrong schedule. Follow the label exactly. As FDA puts it, "If the label says use weekly, don't use it daily,"^[7] and a monthly product given late leaves a gap in which fleas lay eggs.
• A weaker type of product. Flea shampoos and soaps, powders and dusts, spray-on liquids and dips are less effective, and more hazardous to pets and people, than spot-ons, oral products and some collars.^[2] A bath kills the fleas on the pet that day and little else.
• Resistance. Products that worked well in the past may be less effective because flea populations have developed resistance, and veterinarians tend to know which products are performing well locally.^[1]

The fix: reread every label, and if the product seems to have stopped working, ask your veterinarian about switching.

Reason 4: new fleas keep arriving

Pets keep picking up new fleas at kennels and groomers and while moving through yards and neighborhoods, and opossums, raccoons and other wildlife seed fleas into those outdoor spaces.^[1] The way to stop that is to keep pets on a preventive product, seasonally or year round depending on where you live, so stray fleas die before they lay eggs.^[1]

To check the yard: if your pets spend most of their time outdoors, walk the property in white athletic socks pulled high on the leg; adult fleas show up against the white.^[1] Check shaded areas where your pets often lie outside.^[3] Keeping fleas out of the yard covers what to do if you find them.

Reason 5: wildlife is bringing them in

Especially if you don't have pets, rodents and wildlife can bring fleas into your home, and the flea species can reveal animals in the attic or crawl space.^[3] A family of raccoons or opossums in the attic or chimney, or a skunk or feral cat living beneath the house, can be a hidden source of fleas, and the animals should be removed by a nuisance wildlife or pest control professional before the home is treated.^[1] Scratching or thumping overhead at night is a clue; see what animal is living in your attic.

Reason 6: a spot was missed

Pay particular attention to where pets spend much of their time, since most of the eggs, larvae and pupae are concentrated there; if the cat sleeps on a chair or hides under a bed, those spots need treating too.^[1] Closets, the car, a basement couch and a dog's crate are easy to forget. If you are not finding fleas on the pet at all, make sure the bites are fleas; how bed bug bites compare with other bites can help.

Stop and call a pro if

• Adult fleas are still appearing after four weeks of treating every pet and vacuuming daily.
• You have no pets, or you suspect an animal in the attic, chimney, crawl space or under a porch.
• Fleas are biting people heavily and you want the house treated professionally; in Virginia no one may apply or recommend a pesticide commercially without a pesticide business license and a certified commercial applicator on staff.^[8]
• A pet shows signs of a reaction to its flea product, such as trembling, vomiting or seizures; call your veterinarian right away.^[7][6]

Getting help on Loclis

Start with how to get rid of fleas in the house for the full routine, or read whether you need an exterminator for fleas. Browse flea and tick services, find pest control around Blacksburg or see more pest control answers. When you are ready, describe the job on Loclis so licensed pest control businesses can quote it.