Where do fleas come from?


Most flea infestations begin as eggs in shady, wind-protected areas of yards. After maturing, the adult fleas emerge from cocoons and jump onto pets. Infested wildlife, such as raccoons, traverse neighborhoods and deposit flea eggs into yards. Very few infestations begin from adult fleas transferring between animals.


Dispersal of fleas is primarily passive. Although fleas can crawl or jump over short distances, transport from one habitat to another relies mainly on the movement of their primary hosts. Temporary hosts, especially predators of the primary host, also can transport adult fleas from site to site.

Flea Infestations Originate Outdoors

The majority of infestations originate outside. They develop from eggs to larvae to pupae, and eventually exit their cocoons as adults to jump on pets. This commonly occurs in the shaded areas of yards, where cats or dogs frequently rest. Sunny areas can’t support developing fleas.

Infested Wildlife Spread Fleas

Many small animals living in urban neighborhoods can carry cat fleas. Common hosts are opossums, raccoons, foxes, coyotes, skunks, and feral dogs and cats. A survey in Florida found fleas infesting 92.5% of feral cats. In urban Kansas, cat fleas were present on 61.5% of opossums and 21.6% of raccoons. Squirrels and birds aren’t hosts for cat fleas.

As infested wildlife travel through neighborhoods, they continuously drop flea eggs into yards. They’re like living saltshakers, as flea eggs fall anywhere the animals access.

animals that carry cat fleas

Bruce Fingerhood, Greg Schechter, RichardH, DFB Photos, Dawn and Jitze Couperus

Img 1 Common wildlife hosts — raccoon, skunk, feral cat, fox, opossum and coyote.

Urban Wildlife that Carry Cat Fleas
  • Opossums
  • Raccoons
  • Stray cats & dogs
  • Skunks
  • Coyotes
  • Foxes
  • Rabbits
  • Mongooses
  • Hedgehogs
  • Ferrets
  • Weasels
  • Martens
  • Jackals
  • Bobcats
  • Panthers
  • Koalas
  • Marsh Deer
  • Cattle
  • Buffalo
  • Horses
  • Sheep
  • Goats
  • Poultry (rare)
  • Small rodents (rare)
  • Bats (rare)
  • Lizards (rare)
  • Armadillos (rare)

Outdoor Flea Hotspots

Both feral and domestic animals often seek shelter under covered areas. Common examples include structures like decks, porches, and crawlspaces. Hot spots also occur beneath bushes, shrubs, and other vegetation. Flea eggs and feces can quickly accumulate in these places. And fleas thrive in shady, protected habitats. Pets entering these zones can rapidly acquire fleas.

Domestic & Feral Animal Infestation Cycle

Pets can also spread fleas to feral animals. Wildlife enter the yard of an infested pet, and subsequently acquire fleas. The wild animal then further spreads the infestation around the neighborhood. There’s a continual feral–domestic infestation cycle wherever animal territories overlap.

Fleas Rarely Transfer Between Hosts

Dogs and cats seldom acquire adult fleas that jump off of another animal. Fleas rarely transfer hosts. Only 5% of fleas transfer between cage-separated hosts, and 7.5% transfer between animals which live together. It’s also a myth that fleas spread from being scratched off their host and into the environment.

Adult cat fleas are permanent parasites, preferring to remain on their host. They’ll only abandon a dead or dying animal. As a result, new infestations can begin when a predatory animal attacks and kills its flea-infested prey.

Other Flea Sources

Pinpointing where a infestation took root can be difficult. External flea sources may include cars, other homes, as well as parks where many pets are walked. Fleas also occasionally hitchhike on people and get brought into homes to infest pets.

Examples: (1) A friend visits your home along with his infested dog. (2) Your sister agrees to watch your dog, and her home has fleas. (3) You take a road trip, pausing at a rest stop. Your dog lays down in the shade of a tree, where other flea-infested dogs have rested.

Dormant Pre-Emerged Adult Fleas

Within their cocoon, adult fleas can enter a quiescent state that lasts for up to 5 months. Fleas won’t emerge unless heat and physical pressure are detected. These cues indicate a nearby host. Once triggered, fleas emerge in 5 seconds.

Moving into a New Home

People moving into a new home or apartment sometimes encounter fleas, seemingly out of nowhere. This can happen if they don’t have pets. In all likelihood, the previous tenant’s pet had fleas. The fleas developed in the carpet and were in quiescence. When new occupants arrived, the fleas were triggered to wake and emerge.

Sending Infested Pets Away

Similarly, infested pets are sometimes sent away to a veterinary clinic or boarding kennel. During this time, pre-emerged adult fleas are accumulating in the home, waiting for a host before they emerge. When the animal returns home, the fleas exit their cocoon and re-infest the dog or cat.

Wildlife Entering Homes

Wildlife sometimes enter into homes through attics, basements, or crawl spaces. When the animals leave, they’ll have deposited eggs which develop into pre-emerged adults. Eventually the adult fleas emerge to bite people or pets in the home.

Causes for Reinfestation

Flea infestations often go undetected for 3-8 weeks. The population grows until it becomes noticeable. During this time, flea eggs have been continually deposited inside and outside the home. This biomass of immature fleas will be a source of emerging adults for 1-3 months. Pets are at risk of re-infestation from inside the home, and also outside in shaded areas.

Urban wildlife passing through yards can prevent infestations being completely eliminated. At any time, the problem can start all over again. Animals that live in an open environment, as opposed to indoor pets, are at a greater risk of re-infestation.


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  • Darlene Ray August 3, 2017, 9:06 am

    How do wildlife deal with fleas. We recently had a stray dog show up and he was totally covered with thousands of fleas and was extremely anemic and sick. How do wildlife animals keep from getting this infected? We live in the country in Illinois and this year has been horrible for fleas and ticks. Several dogs have contracted Lyme disease from deer ticks and died of kidney failure. One of our labs died last year from undetected Lyme Disease so how do wlldlife fare with so many fleas and ticks in the wild?

    • Adam Retzer August 13, 2017, 4:38 pm

      I am not sure about ticks. But with fleas, the infestations aren’t usually that severe (thousands of fleas). In geographic parasite surveys, the normal population on animals rarely exceeds a couple dozen. Extreme infestations (above a couple hundred) are rare. Host grooming is the primary cause of flea death. Animals continually exposed to flea bites develop some resistance to the effects of their bites, so they wouldn’t be as itchy as those that aren’t bitten often.

  • Lorraine Benninghoff November 18, 2017, 6:49 pm

    My dog doesn’t have fleas but we have fleas for the first time in 30 years in our home. They seem to only be on our couch. If we take the couch outside when it is below freezing out and leave it out there for several hours will that kill the fleas and any eggs that may be there?

    • Adam Retzer November 19, 2017, 3:44 pm

      Exposure to below freezing temperatures should kill all flea stages. However, you may want to leave it outside for longer than several hours. Parts of the couch may be insulated and may not reach subfreezing temperatures quickly. Read our article on Do fleas die in the winter?. You’ll probably want to leave the couch outside for at least 5 days.