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University of Minnesota Extension


Quick Facts 

  • Fleas are primarily pests of animals but will bite people.
  • Treat fleas on pets and in the home at the same time.
  • The most effective flea treatments for pets are oral or topical spot-on medications or medicated collars.
  • Treating pets preventatively is easier and more effective than treating after a flea problem occurs.
  • Before using any flea or tick treatment on a pet, ask your veterinarian about the most appropriate product. Using the wrong product could cause medical problems for your pets.
  • When treating homes, use a combination of nonchemical and insecticide methods for the best results.

Fleas are parasites of many animals including cats, dogs, rodents, birds and bats. The cat flea (Ctenocephalides felis) is the most common flea that infests homes and attacks humans and pets.

How to identify fleas

Close-up image of adult flea
Adult flea

Adult fleas

  • Dark brown to black, less than 1/8 inch long.
  • Wingless; body is flattened from side to side.
  • Large hind legs for jumping.


  • About 3/16 inch long.
  • Whitish; resemble tiny worms.

Dark, pepper-like dried blood and dark reddish-brown or black flea excrement (called “flea dirt”) may be found on pets or their bedding.

Flea dirt in pet hair.
Watch for dark, pepper-like flea dirt on pet fur and bedding

Biology of fleas

Adult fleas

  • Feed on blood and spend almost their entire lives on their hosts.
  • Their favorite hosts are cats and dogs, but they also feed on wildlife, including raccoons, opossums, skunks and foxes.
  • Fleas can bite people but females require a blood meal from a non-human host to produce eggs.
  • Female fleas lay 4 to 8 eggs at a time and can lay as many 500 eggs in their lifetime.
  • Adults may survive for weeks without a blood meal.

Flea eggs

  • Nonsticky and typically fall to the ground.
  • After 2 to 5 days, eggs hatch into small, white, worm-like insects.
  • Larvae feed on flea feces (commonly referred to as flea dirt), which is largely composed of undigested blood.
  • Larvae normally take about 7 to 15 days to finish their development.
  • They avoid light and require humidity above 75%.
  • Eggs can take up to six months to develop into larvae if temperatures and humidity are unfavorable.


Close-up of flea larva.
Flea larva
  • Larvae make cocoons where they become pupae and remain for weeks or months.
  • Pupae can take 12 months or longer to develop into adults if temperatures and humidity are unfavorable.
  • Adult fleas emerge when cocoons are stimulated by warmth, carbon dioxide (breath), and pressure or vibrations (someone walking or vacuuming).
  • Adult fleas live for 1 to 12 months.

How fleas are harmful

Fleas are generally pests of animals, and dogs and cats serve as their primary hosts in homes. Adult fleas readily bite pets for a blood meal.


  • Can experience dermatitis as a result of flea bites.
  • Biting causes itching, reddening of the skin and further skin irritation.
  • Fur loss can also occur and in extreme cases, animals may become anemic.
  • Speak to your veterinarian about any animal health concerns associated with pets.


  • Adult fleas bite and feed on blood.
  • Often it results in raised, red bumps that itch.
  • Symptoms may persist for five days or more.
  • Bites typically occur in clusters on lower legs.

Some people do not react to flea bites and may not notice their presence. Other people may experience flea bite allergic dermatitis, resulting in more intense itching, hair loss and reddening. Scratching these areas may result in secondary infections. Speak to your physician about any health concerns associated with flea bites.

Caution: It is very challenging to diagnose flea bites only from lesions as other causes can look similar. The best method for verifying fleas is to find adult fleas on pets or in the home.

While fleas can technically transmit several diseases to people, like plague and murine typhus, cases of these diseases have not been found in Minnesota. Fleas are known to transmit tapeworms to dogs and cats in Minnesota.

How to control fleas

It is important to control fleas on your pets at the same time as in your home. Use a combination of nonchemical methods and insecticides to control fleas in your home.

You can have a flea problem even if you don't have pets. Wild animals such as raccoons, opossums or squirrels nesting in the attic, fireplace or crawlspace, can bring them in. Treat these areas, seal holes or other possible entryways so animals can't get back in, and remove wild animal hosts to control fleas in these situations.

Fleas are rarely found in lawns or other outdoors sites on your property in Minnesota, as they do not survive winter temperatures.

Treating pets

  • Dog laying on white dog bed
    Talk to your veterinarian about the best flea product for your pet
    It is very important to treat pets at the same time the home is treated. 
  • Be sure to consult your veterinarian for help in selecting a specific product to treat your pet. 
  • Different breeds of cats and dogs can also have different tolerances to particular active ingredients.
  • It is critical to follow all product directions to ensure effectiveness and safety. 

Preventing fleas on pets

Preventing fleas on pets is easier than treating infested animals. It can take several months to eliminate moderate to severe flea problems on pets. 

The most effective preventive medications are topical spot-ons and oral chewable tablets. These products are very effective and long-lasting (one to three months depending on the product).

Products used for prevention can also be used for treating existing problems.


CAUTION: Before using any flea or tick treatment on a pet, consult with your veterinarian to discuss the most appropriate product(s). Using the incorrect product could pose medical concerns to your pet.

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

Treating fleas in homes

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

Jeff Hahn, Extension entomologist, and P.J. Liesch, entomologist, University of Wisconsin

Reviewed in 2020

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