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 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 animals, and their bites can lead to health problems.

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, rodents and similar smaller 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 (20-30 is pretty common). The eggs are laid on the host but will quickly fall off that host into the environment. They land on pet bedding, carpet, wood floors, upholstery, etc. Inside a home, eggs typically hatch within about two to three days.
  • Larva: When the eggs hatch, the larvae emerge. These tiny worm-like creatures feed primarily upon flea feces in the environment (this is essentially dried blood) and unhatched eggs. The larva goes through three stages of growth before it spins a cocoon and enters the pupal stage. The larval stage typically lasts from 5 to 15 days under the conditions found within most homes.
  • Pupa: Within its cocoon, the pupa begins its transformation into an 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 generally not emerge until they sense a host. They can do this by sensing factors like warmth and pressure.
  • Adult flea: The newly-emerged flea jumps on the host and begins the blood meal as quickly as possible. A female flea will usually begin to lay eggs within two days of her first blood meal. She defecates blood from her host that will fall off the host along with the eggs, restarting the life cycle. Adult fleas typically live for about a week or two on pets but can survive much longer under ideal, artificial conditions.

Now that you know the life cycle of a flea, you can understand why some dogs get infested with fleas soon after moving into a new home or 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, scratching, skin damage, and 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, the host animal can 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 die or suffer medical complications as a result of anemia.
  • Tapeworm infection (Dipylidium caninum): This type of tapeworm can be contracted after the accidental ingestion of an infected flea (during self-grooming, for example). Flea larvae often ingest the microscopic tapeworm eggs, causing adult fleas to be carriers.
  • Fleas play a role in the spread of typhus, plague, and bartonellosis.

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 all year round. 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.