What to Know About Fleas

Scratching Dog

The La Crosse Veterinary Clinic has created a Flea Questionnaire to help pet parents know how to start controlling these pests.

We speak with clients every day that know someone or are someone that has a current flea infestation.  A lot of these people Flea Illustration aren’t aware of the flea realities and some have fallen to the flea myths.  It’s disheartening to know that most of these pets could have been saved from ever getting fleas with the right monthly preventative.

I always tell a client who is struggling with fleas that it can be helpful to understand the life cycle of a flea.  Below, outlined is some very important facts including information about the life cycle.  It is very important to know that there is no “magic treatment” that will cause fleas to disappear instantly.  Flea infestations can take several months to get rid of, but understanding how will make all the difference.


  • They are about the size of the tip of a fine point writing instrument. Oval in shape and white in color.
  • 40-50 eggs per flea are laid on the host and most fall into the pet’s environment within a few hours.


  • Larvae look like maggots but much smaller. They are approximately 0.5cm long, about the size of a grain of rice.
  • Larvae feed on blood in adult flea feces, organic debris like dead skin, flea eggshells and other flea larvae.
  • Flea larvae will develop in areas that are undisturbed like under furniture, along baseboards and in carpets. Outside, this could be in bushes or grasses where your pet lays. They do not develop where there is a lot of sun.
  • The time it takes for larvae to develop into pupae depends on temperature and humidity.


  • This is the hardest stage to control. It is water tight and not affected by sprays or chemicals.
  • Vacuuming, cleaning and unfortunately, encouraging them to hatch, are the best ways to exterminate the pupae.
  • Pupae (or cocoons) are found in soil, bushes and grasses, in carpets, on bedding where the pet lays and are 0.5cm long.
  • Pupae may begin emerging into an adult flea around 8 days after starting the pupal development but may remain in the cocoon for up to 30 weeks. The average time to transform from larvae to pupae is 13 days.
  • The cocoon is stimulated to hatch by temperature and the activity of people or animals.


  • Adult fleas emerge from the Pupae stage around 21-35 days; emerging faster if it is warmer
  • Fleas begin feeding on the host immediately. Blood is then excreted on the host and resembles pepper flakes.  This is called “flea dirt”.
  • 20-24 hours later egg production begins and 40-50 eggs are produced per day.
  • Adult fleas can live 2-3 months long and can lay eggs every day.


Cat ScratchingFlea Facts


  • Fleas can withstand cold conditions for 10 days. Longer if they are in a pupal stage.
  • They can continue their life cycle through the winter while living on dogs, cats, rabbits, birds, squirrels, etc.


  • Anemia from an iron deficiency and death especially in young animals are from heavy flea infestations.
  • The common flea can transmit Bartonella hensalae (also known as Cat Scratch Fever), tapeworms, blood parasites, tularemia, and even the bubonic plague.
  • Flea allergy dermatitis (FAD) is an allergy to the flea saliva & causes a skin reaction.


  • Physically observing adult fleas on your pet
  • Using a flea comb on the pet over a wet paper towel. The “flea dirt” will turn red resulting in a positive flea test.  Remember, “flea dirt” is dried blood.


  • Veterinary recommended flea control products:
    • Frontline Plus (Canine & Feline)
    • Sentinel (Canine)
    • Nexgard (Canine)
    • Capstar (Canine & Feline)
    • Program Injection (Feline)
    • Siphotrol (Home spray)
  • Ask your veterinarian about what is currently recommended and what would be best for your pet
  • A large flea infestation can take several months to control.
  • Many people will see a drop in flea activity after 2 weeks of treatment. This does not mean that the fleas are gone, they just have not hatched yet. Keep treating your pet and environment.
  • Occasionally, the flea control product recommended to you will not meet your expectations. A number of variances may be the cause.  Please ask your veterinarian if additional measures should be taken, such as environmental control.

Source: https://www.capcvet.org/capc-recommendations/fleas/

 Now that you have learned more than you may want to know about fleas, you are prepared for the war!  If you are looking for more answers to fleas, visit these sources:

What you need to know about fleas, a quick read on the basics of fleas.

La Crosse Veterinary Clinic FAQ’s page frequently asked questions.

Companion Animal Parasite Council an independent council established to create guidelines for the optimal control of internal and external parasites.

VeterinaryPartner.com is a good source for animal health, medical conditions, therapies, surgery, behavior and much more.

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