Fleas on Dogs and Their Life Cycle

Flea, Cat or Dog (Ctenocephalides sp) 10X at 35mm. Ectoparasite, wingless insect, flattened laterally. Siphonaptera
Ed Reschke/Photolibrary/Getty Images

If you know about dogs, then you probably know what fleas are. You surely know that you don't want to see fleas in your home, on yourself, or on your dog. However, these parasites are more than just a nuisance.

Fleas pose a significant health risk to dogs and other animals, including humans. These tiny external parasites feed on the blood of mammals, and their bites can lead to major health issues.

As a dog owner, there are some basics you should know about the risks, prevention, and treatment of fleas. With proper knowledge, you can help protect your dog and your home from fleas.

About the Flea

The flea is a tiny wingless insect with a hard and laterally flat body designed to easily navigate through pet hair. The flea also has legs designed for jumping great distances and mouthparts designed to suck blood. This parasite feeds upon the blood of a host, usually a mammal.

There are several species of fleas, but the one that most commonly affects dogs, cats, and other house pets in North America is the cat flea, also known as Ctenocephalides felis. While this type of flea can and will bite people, humans are not an ideal host. This flea prefers cats, dogs, rabbits and similar small mammals.

The Life Cycle of Fleas

The flea life cycle has four stages.

  • Egg: An adult female flea can lay up to about 40 eggs a day. The eggs are laid on the host but will dry and fall off that host into the environment. They land on pet bedding, carpet, wood floors, upholstery, etc. Eggs typically hatch within about two days.
  • Larva: When the eggs hatch, the larvae emerge. These tiny worm-like creatures feed upon flea feces in the environment (this is essentially dried blood) The larva goes through three molts before it can spin a cocoon and enter the pupal stage. The larval stage typically lasts from 5 to 15 days.
  • Pupa: Once in the cocoon, the larva begins its transformation into the adult flea. The cocoons are nearly indestructible and attract dirt and debris that camouflage them. Pupae can remain dormant in the environment for many months. Fleas in the pupa stage will not emerge until they sense a host. They are able to do this by sensing factors like warmth, vibration, and carbon dioxide from host exhalation.
  • Adult flea: A fully-developed flea only emerges from its cocoon when a host is available. The newly-emerged flea jumps on the host right away and begins the blood meal. A female flea will begin to lay eggs within 24-48 hours of her first blood meal. She defecates blood from her host that will fall off the host along with the eggs, re-starting the life cycle. Adult fleas can live for about 4-6 weeks depending on the environment.

    Now that you know the life cycle of a flea, you can understand why many dogs get infested with fleas soon after moving into a new home or even visiting a new place that has been free of pets for a few months. The pupae emerge as soon as they sense a host. One dog can suddenly have hundreds of fleas that seem to have come out of nowhere! Within a couple of days, the fleas are reproducing like crazy and the infestation can seem out of control.

    The Dangers of Fleas on Dogs

    Beyond the obvious fact that a flea infestation is disgusting, fleas also pose health risks to you and your pets.

    • Flea Allergic Dermatitis: Itching from fleas is caused by a localized allergic reaction to flea saliva. Some animals are more sensitive than others, so flea bites can lead to severe itching, irritation, major skin infections in some pets. Other pets will not seem to react at all to the fleas because they do not have the same allergic reaction.
    • Anemia: If enough fleas infest the host, it is possible for the host animal to lose enough blood to become anemic. Small puppies and weak or sickly dogs are especially at risk. If not caught soon enough, a dog can easily die or suffer other medical complications as a result of anemia.
    • Tapeworm infection (Dipylidium caninum): This type of tapeworm can be contracted after accidental ingestion of an infected flea. Flea larvae often ingest the microscopic tapeworm eggs, causing adult fleas to be carriers.

    Not all dogs are allergic to fleas. Some dogs will ignore the fleas on them and you may not even notice there is a flea problem in your home. However, these dogs can still get tapeworms and even anemia.

    The best way to keep your dog safe from fleas is to prevent a flea infestation in the first place. It's important to check your dog for fleas periodically and give flea prevention to your dog regularly. Keep fleas from disrupting your life and the lives of your pets and your family. 

    If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.