Where do fleas come from?


Most flea infestations begin as eggs in shady, protected areas of yards. Once they reach adulthood, the fleas emerge from their cocoons and jump on 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 of these insects from one potential habitat to another relies mainly on the movements of their primary hosts. Temporary hosts, especially predators, 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, 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.

Flea dispersal is primarily passive. Though they can jump or crawl short distances, transport from one habitat to another relies mainly on their primary host. 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 have access to.

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 quickly accumulate in these locations. And fleas thrive in shady, protected habitats. Pets entering these zones can rapidly acquire fleas.

Domestic & Feral Animal Infestation Cycle

Conversely, pets can spread fleas to feral animals. Wildlife ranging through urban environments may enter the yard of an infested domestic animal, 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 fleas that jump off of another animal. It’s rare for fleas to 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 the area where a flea infestation took root can be difficult. External flea sources may include cars, other homes, as well as parks where many owners are walking with their pets. 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 (dormant) state. This pre-emerged state can last for up to 5 months. Fleas won’t emerge unless heat and physical pressure are detected—two cues which indicate a nearby host. Once triggered, they’ll 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 lying dormant. When new occupants arrived, the fleas were triggered to 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

It’s also possible for wildlife to 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 become noticeable. By 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 outside in shaded areas.

Urban wildlife passing through yards can prevent infestations from ever getting completely eliminated. 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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