Fleas Under the Fur. How Cats and Dogs Get Infested Differently in Pictures


Cat fleas (Ctenocephalides felis) and dog fleas (Ctenocephalides canis) are two common external parasites that affect cats and dogs. While they may look very similar, cat and dog fleas have some key differences in terms of appearance, host preference, breeding habits, feeding behavior, potential to spread disease, treatment options, prevention methods, and environmental factors.

The purpose of this article is to provide a comprehensive overview comparing and contrasting cat fleas versus dog fleas. Understanding the differences between these two pests can help pet owners better protect their cats and dogs.


Cat and dog fleas look very similar, but there are some subtle physical differences between the two species. Both cat and dog fleas are very small insects, about 1-3 mm in length. Dog fleas (Ctenocephalides canis) tend to be slightly larger than cat fleas (Ctenocephalides felis).

Under a microscope, the easiest way to distinguish between cat and dog fleas is by looking at the genal comb, a row of spines on the head. Cat fleas generally have 5-6 spines in the genal comb, while dog fleas have 7-8 (1). The spines help stabilize the flea when it jumps between hosts.

Dog fleas also tend to have thicker and longer rear legs compared to cat fleas, which enables them to jump higher and farther. Cat fleas have rear knees that extend above their backs, while dog fleas’ knees do not extend above their backs (2).

Despite these subtle physical differences, cat and dog fleas are extremely similar in appearance. Examining their genal comb and back legs under a microscope is the most reliable way to tell them apart.

(1) https://www.pinterest.com/pin/33495590955320094/

(2) https://www.pinterest.com/pin/how-to-get-rid-of-fleas-naturally-shtfpreparedness-in-2023–1034279870652356740/

Host Preference

Although cat fleas and dog fleas are different subspecies, they are capable of living on both cats and dogs. However, each subspecies prefers and thrives better on their namesake host.

Cat fleas (Ctenocephalides felis) prefer cats as hosts and will thrive better on them. As reported on Quora, “Whilst it is true that cat fleas can certainly use dogs as a host, (animal that the flea gets its blood meal from), fleas prefer the species that they evolved to live on, which in the case of cat fleas is cats.” (Source)

Similarly, dog fleas (Ctenocephalides canis) prefer dogs as hosts. The Merck Veterinary Manual states, “Cat fleas that have found a preferred host (eg, dog, cat, opossum) and have initiated reproduction generally do not leave their host unless forced off by insecticides or for lack of a blood meal.” (Source)


Cat and dog fleas prefer to live on their hosts, but they must lay eggs in the environment for their life cycle to continue. Female fleas will periodically leave the host to lay eggs in places like carpet, bedding, crevices, and vegetation. According to Merck Veterinary Manual, flea cocoons containing larvae and pupae can be found in soil, under vegetation, in carpets, under furniture, and on animal bedding. Flea eggs hatch into larvae within 2-12 days, and the larvae feed on organic debris before spinning a cocoon and entering the pupal stage. After 1-2 weeks in the cocoon, the adult flea emerges when stimulated by vibrations, warmth, carbon dioxide, or other signs of a host. Newly emerged adult fleas then jump onto hosts to feed and mate.

The Hartz article notes that while adult fleas live on pets, the eggs, larvae, and pupae develop off-host in areas like carpets, crevices, bedding, and vegetation. Female fleas must leave the host periodically to lay eggs in these areas, enabling continuation of the flea life cycle.

Biting and Feeding

Fleas have specialized mouthparts called a siphon that allow them to pierce the skin and feed on blood. When a flea bites, it uses two tube-like structures – one injects saliva into the bite wound to prevent blood from clotting, while the other sucks blood from the host.

Cat and dog fleas prefer feeding on pets, but will readily bite and feed on humans as well if given the opportunity. They are able to sense the presence of a nearby host through body heat, vibrations, and exhaled carbon dioxide.

Once on the host, fleas quickly locate a blood vessel using specialized sensory organs on their legs and mouthparts. They pierce the vessel using their siphon and feed rapidly, often finishing a blood meal within just a few minutes.

Flea saliva contains compounds that numb the area and prevent clotting during feeding. This allows the flea to feed freely, but can lead to significant blood loss for the host. Flea bites are usually located around the legs and ankles in humans.

The flea’s rapid vessel feeding strategy allows it to finish a blood meal quickly before detection. But it can also lead to serious discomfort for the host, including red bumps, rashes, and significant itching from flea saliva allergens. Vigorous scratching of flea bites can further damage the skin.

For more details on how cat and dog fleas bite and feed, see this in-depth article from FleaScience.com: How do fleas bite and feed?


Fleas can transmit a number of diseases to cats, dogs, and humans. Some of the most common flea-borne diseases include:

Bartonellosis (also known as cat scratch disease) – Caused by the bacterium Bartonella henselae and transmitted through flea feces. Infects both cats and humans. Symptoms in humans include swollen lymph nodes, fever, and fatigue. See 4 Common Flea Diseases in Cats.

Tapeworms – Flea larvae ingest tapeworm eggs, which develop into cysts inside the flea. When a cat or dog grooms itself and ingests an infected flea, the tapeworm larvae are released into the intestines and develop into adult tapeworms. Signs include digestive issues and visible worm segments around the anus. See Beyond the Itch: 6 Flea Diseases in Cats and Dogs.

Flea allergy dermatitis – An allergic reaction to flea saliva. Most commonly causes severe itching, hair loss, and skin lesions in dogs and cats. See Flea Borne Diseases in Humans, Cats & Dogs.

Anemia – Can occur if a pet has a major flea infestation. The fleas feed on large amounts of blood, leading to anemia and pale gums.


There are several effective treatment options for getting rid of fleas on cats and dogs. Topical spot-on treatments like Frontline or Advantage are very effective at killing fleas and flea larvae. They are applied monthly to the skin at the back of the neck and spread over the body via the natural oils in the skin. Oral treatments like Capstar, Nexgard, or Bravecto are also options. These oral pills kill fleas within hours and provide longer protection. Flea collars impregnated with insecticides can also be used. Regular bathing with flea shampoos containing pyrethrins or insect growth regulators helps kill fleas on the skin. The environment must also be treated by vacuuming regularly and washing bedding at high heat. Using sprays, powders, or foggers helps kill flea eggs and larvae in crevices and fabrics. Be sure to treat all animals in the household and follow up with monthly topical or oral treatments.


There are several ways to prevent flea infestations in cats and dogs. The most effective prevention is using flea control products recommended by your veterinarian. Topical flea treatments like Frontline, Advantage II, or Seresto collars can kill adult fleas and eggs while also repelling new fleas. Oral flea preventatives like Nexgard or Bravecto are also highly effective. It’s important to use flea prevention year-round, even during colder months when fleas are less active.

Flea prevention should be used on all pets in a household. Thoroughly vacuum and wash all pet bedding weekly to remove eggs and larvae. Regular bathing and grooming can help remove fleas and eggs from your pet’s coat. Keep your home and yard clean by mowing grass short, clearing brush, and removing any standing water sources. You can also use sprays and foggers indoors or spray insecticides outdoors around kennels and play areas. Be sure to talk to your vet before using any pesticide products on your pet or in your home.


Cat and dog fleas thrive in warm, humid environments. According to Hartz, the three most common places fleas are found are:

  • On cats and dogs – Adult fleas prefer to live on the back, neck and underside regions of cats and dogs. Their eggs, larvae and pupae live in the host’s bedding and surrounding environment.
  • Carpets and rugs – Flea eggs and larvae can be found deep down in the fibers of carpets and rugs. The warmth helps them thrive and develop.
  • Yards and gardens – Fleas are likely to infest areas where pets spend time, like yards and gardens. They can live in shrubs, grass and soil.

Fleas can survive without a host for many months given the right conditions. They prefer warm, moist environments both indoors and outdoors. Reducing humidity levels can help control flea populations. Frequent vacuuming and washing of bedding are also recommended.





In summary, while cat and dog fleas are the same species (Ctenocephalides felis), they exhibit some key differences in appearance, host preference, breeding habits, biting behavior, potential for disease transmission, treatment approach, and optimal prevention strategies. The cat flea is more prevalent on pets, able to survive indoors, and lays eggs in the carpet. Meanwhile, dog fleas prefer outdoor, shaded areas. Both fleas can cause skin irritation, anemia, and transmit diseases. However, cat fleas pose a greater threat to humans. Effective flea control requires treating both the pet and home environment, and prevention is critical to break the flea life cycle. While challenging to eliminate, understanding the nuances of cat and dog fleas can help pet owners and pest management professionals target the pests appropriately.

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