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Flea Prevention

Fleas can be very frustrating for owners and their pets. They not only cause itching and dermatitis but can transmit parasites, such as tapeworms. Sometimes it may seem as though a flea infestation persists even with the use of a flea preventative. It is important to understand the flea lifecycle and how flea preventative products work in order to best protect your pet from a flea infestation.

Fleas Life Cycle


The flea life cycle involves four different life stages:

1.  Eggs - Flea eggs are very small, about 0.5mm in length. An adult flea will lay up to 50 eggs per day. The eggs fall off of the host (dog, cat, etc) and into the environment. If your pet is inside when eggs are laid, they will fall into the carpet, rugs, and furniture where your pet spends its time. The eggs are not sticky, so they can sometimes be removed with a vacuum. However, the eggs are so small that sometimes they fall too deep into the carpet for a vacuum to completely remove. Eggs hatch 1-12 days after being laid depending on the type of environment. Most of the time eggs will hatch in 2-3 days.​

2.  Larvae - Larvae hatch from the eggs and are 3-5mm long. They seek our dark areas such as cracks in the floor, under furniture, or deep in the carpeting. Larvae feed on the feces from adult fleas, food particles, skin cells, and dead insects. The larval stage 4-18 days after which the larvae spin a cocoon around themselves and enter the next life stage.

3.  Pupae - When fleas are in the pupal stage they are very hardy. The cocoon protects the larvae from insecticides and desiccation. The cocoon is also very sticky making it difficult to remove from the environment. This is often the life stage that leads to a persistent flea infestation because they are difficult to remove or kill. The flea is typically in the pupal stage from 5-10 days, but can survive for up to 6 months. The flea must eat a blood meal within one week of emerging from the cocoon or it will die. If there are no suitable hosts, the flea will remain in the pupal stage until a host is present. When a host is nearby, the flea senses its presence and will emerge from the cocoon.

4. Adult - Adult fleas are about 2.5mm long and are the most commonly noticed stage of the flea life cycle. They have long, powerful legs that are used to jump onto their host. Adult fleas live on a host for two to three months. Female fleas can lay up to 50 eggs per day or 4500 eggs in their lifetime. Fleas feed on blood from their hosts. They inject a numbing agent while feeding so the host does not feel the bite. However, flea saliva can cause skin irritation and lead to itching. Adult fleas are the easiest life stage to kill because they are susceptible to insecticides, vacuuming, and manual removal.

Overall, the flea life cycle can occur in as short a period as two weeks or last for several months. This is important to understand so that flea preventatives can be used effectively to eliminate a flea infestation.

Flea Eggs

Flea Preventatives


There are a variety of oral and topical flea preventatives and insecticides that can be used on cats and dogs to kill fleas. These products will kill the adult stage of the flea and some will kill eggs and/or larvae. Products may take anywhere from a few minutes to several hours to start killing fleas. Most flea products require a flea to bite the pet before it will be effective, but some include a repellant action. Below are some common flea preventative products and the differences between them.

Dog Flea Preventatives
Canine Flea Prevention

The mode of action refers to how the flea is affected by the preventative product. “Bite” means that the flea must bite the dog to be affected while “repellant” means that the product helps to repel fleas.

Cat Flea Preventatives
Feline Flea Preventatives

 The mode of action refers to how the flea is affected by the preventative product. “Bite” means that the flea must bite the cat to be affected while “repellant” means that the product helps to repel fleas.

Diseases caused by fleas


Fleas are best known for causing irritation, scratching, and dermatitis, but they can cause other diseases as well.


  • Allergies: Some dogs are more sensitive to the irritation caused by flea saliva leading to a flea allergy. Flea allergy is the most common type of allergy in dogs and cats. Flea allergy dermatitis is most common near the base of the tail and along the top of the back. Cats may also develop dermatitis around their ears, chin, and neck. Flea allergy dermatitis is more likely to occur when flea control is inconsistent. In addition, flea allergies can enhance the response to other allergens, such as pollen, dust mites, and grass.

  • Tapeworms: Fleas play an important role in transmitting tapeworms. Flea larvae eat tapeworm eggs, which then develop inside the adult flea. When a dog or cat is grooming or scratching at fleas and ingest them, they also take in the tapeworms inside the flea. While the flea is digested, the tapeworms emerge and mature in the dog or cat.

  • Bartonella: Bartonella is the name of a group of bacteria that can be transmitted by fleas, and can infect dogs and cats as well as humans. Bartonella bacteria invade red blood cells and can cause a variety of diseases depending on the bacterial strain. One strain of Bartonella is responsible for cat-scratch fever in humans.

  • Feline Infectious Anemia (FIA): This disease is caused by the bacterium Mycoplasma hemofelis. It is transmitted between infected cats by flea bites. The bacteria attach to the outside of red blood cells and weaken the cell membrane enough that the cell bursts. In addition, the cat’s immune system tries to get rid of the bacteria but often destroys the affected red blood cells in the process. This can lead to anemia, which can become severe depending on the stage of the infection. Cats affected by FIA may show signs such as anorexia, weight loss, lethargy, weakness, pale gums, vomiting, fever, rapid breathing, heart arrhythmias, icterus (jaundice), and kidney failure. FIA can be fatal if it goes untreated.

Goals for Flea Elimination and Control

When dealing with a flea infestation, it is best to keep three goals in mind: 

Goal 1 - Relieve your pet’s discomfort by killing the fleas that are currently feeding on your pet.

Your pet’s discomfort is caused by a reaction to the flea saliva, so relief is only achieved by killing the fleas that are currently feeding on your pet. This can be accomplished by using a flea preventative or insecticide with a fast killing action. Residual duration is beneficial to allow for the killing of any fleas that will subsequently jump onto your pet. For example, while a flea shampoo will kill any fleas that are currently on your pet, it does not have residual action. So, as soon as the shampoo is rinsed off, fleas can jump on your pet and continue feeding. Using a flea preventative that has a repellant action can be beneficial especially for pets that are demonstrating signs of flea allergy dermatitis or are at high risk of flea exposure. These preventatives will kill any fleas that are on your pet, but they will also repel future fleas that your pet encounters. We recommend using one of the veterinary prescription products listed above to protect your pet. Over the counter products may not be as effective or have as long of a duration. Some over the counter products can have toxic effects on your pet if used incorrectly. If your pet has dermatitis from the flea infestation, they may have a secondary bacterial infection as well. If this is the case, we may recommend an antibiotic to treat the infection as well as medication to reduce inflammation.

Goal 2 - Eliminate the flea infestation on the premises including eggs, larvae, and pupae.

Elimination of fleas on the premises is very important for preventing future flea infestations on your pet, but it is often difficult to achieve. Flea eggs, larvae, and pupae that are present in your house or yard will develop into adult fleas that can then infest your pet. It can take several months to completely eliminate fleas from the premises due to the potentially long life cycle, and you may never completely eliminate fleas from your yard. There are several points to consider when addressing this goal:

  • All pets in the household should be treated for at least three months. Fleas can infest dogs and cats as well as rabbits, ferrets, hedgehogs, and guinea pigs. All pets should be treated with a preventative because if there is an untreated pet in the household, it will serve as a source for flea feeding and reproduction. If a monthly dose is missed or delayed, elimination of fleas may fail because new adults can develop during that time, feed on the untreated animal, and produce 40-50 new eggs per day. If all pets are treated with an effective preventative for three to four months, a flea infestation can be eliminated.

  • Flea eggs, larvae, and pupae present in carpets, rugs, furniture, and bedding will continue to mature. Newly matured adult fleas may be seen on pets even after applying a preventative because they have not yet taken a blood meal and been affected by the preventative. Treating your home can help to break the flea life cycle and further reduce exposure of your pet to fleas. We recommend using a spray insecticide that can be targeted underneath furniture, radiators, appliances, and baseboards. Be sure to follow the label directions to ensure that products are used appropriately.

  • Identify sources of new infestations. Fleas are present on a variety of wildlife including squirrels, foxes, coyotes, raccoons, opossums, and feral cats. If these animals pass through your yard, flea eggs present in their coat will be deposited wherever they travel. Flea eggs and larvae will be especially prevalent in dark, protected places, such as under bushes, shrubs, and porches, in crawl spaces, or in barns. Treatment of your yard with insecticides may help to reduce the exposure of your pet to fleas. However, since wildlife can continually reintroduce fleas to a treated yard, it is usually more effective to use a flea preventative with residual protection on your pet.

  • Even if your pet does not spend time outside (such as an indoor cat), fleas can be transported into your house on human clothing. Fleas may come inside on your shoes, boots, or pant legs. In addition, flea eggs, larvae, or pupae can be brought into the house in dirt and mud on the soles of your shoes. Therefore, we recommend using a flea preventative on all pets even if they are spending minimal or no time outside.

  • While cold weather will reduce the number of fleas present outside, it is important to remember that fleas can survive the winter in protected places such as a garage, shed, or barn. If your pet is spending time in these areas, they could be at risk of becoming infested. It can be beneficial to use a flea preventative on your pet year-round especially if your pet has a flea allergy.


Goal 3 - Prevent future infestations.

Once a flea infestation has been resolved, it is important to continue flea preventatives in order to protect your pet from reinfestation. As mentioned previously, your pet can be continually exposed to fleas in the outdoor environment. Flea preventatives will kill those adult fleas before they can reproduce and establish an infestation in your home. We recommend life-long use of a flea preventative on all pets either year-round or seasonally - start in the spring when the weather is consistently above 50 and continue until after a hard frost in the fall.

Top 10 Flea Myths 

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