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Compendium April 2011 (Vol 33, No 4)

Flea Control: Real Homes, Real Problems, Real Answers, Real Lessons: Fleas in a Flash!

by Michael W. Dryden, DVM, MS, PhD, Doug Carithers, DVM, EVP, Michael J. Murray, DVM, MS, DACVIM


    This is the first of a five-part series of cases that formed part of a field-study research project conducted by the Kansas State University Flea Team in 2009 in Tampa, Florida. BOX 1 describes the criteria for inclusion and the methods used in this study.

    In this case, you will learn where in their own yard pets are most likely to acquire new fleas, what other animals might share the yard, and how quickly new fleas can jump onto pets.


    Flea control has always been difficult. The advent of modern flea control products with excellent month-long activity against fleas and/or their eggs has had a tremendous impact on flea control; however, for some pet owners, flea control still seems problematic. Consequently, veterinary practices continue to get cases in which it appears that the flea control product they sold failed to work.

    It is often not possible for the veterinary clinic to get to the root cause of all of these cases. Flea biology and its interaction with the environment and flea hosts are complex, and it is not feasible for veterinary staff to conduct in-home investigations. This series of cases illustrates real examples of challenging flea control situations in which owners continued to see fleas on treated pets. By understanding the results of these investigations, you and your staff can see how complicated flea infestations can become and why simply blaming product performance is not a solution.

    Essentials for Understanding Flea Biology and Flea Control

    Before examining this case, it is essential to understand the following facts about flea biology and flea control:

    • As an adult, Ctenocephalides felis felis, the cat flea, is an obligate parasite that is metabolically and reproductively bound to its host.1–3 This revelation dramatically changed approaches to managing fleas: by applying products to and on pets, owners and veterinarians attempt to control reproduction and “break the life cycle” rather than focusing on the environment.4–6
    • Once on a preferred host, cat fleas begin feeding within minutes and start breeding soon after. A female flea can begin laying eggs within 24 to 48 hours of jumping onto a host. In a few days, a female flea can lay 40 to 50 eggs/day.2
    • Flea eggs roll off the host, and larvae typically hatch in 3 to 5 days. The larval stage is the most sensitive. Flea larvae require flea feces for nutrition, protection from direct sunlight, temperatures in the range of 45°F to 90°F, and relative humidity in the range of 50% to 85%.7,8
    • The rate of flea development depends on the temperature. Development from eggs to fleas can take less than 3 weeks at 85°F and can take 7 to 12 weeks at 65°F.7,8
    • New fleas develop and emerge where pets or other flea hosts spend most of their time because this is where the most eggs and feces are deposited, and larvae require flea feces for nutrition.
    • Common hosts for C. felis include cats, dogs, opossums, raccoons, domestic rabbits, and hedgehogs.7,8 Squirrels and birds are not hosts for cat fleas.
    • Feral cats, opossums, and raccoons move throughout neighborhoods. These “urban wildlife” hosts for the cat flea often seek shelter in covered, protected areas, and wherever they rest, they leave behind flea eggs and flea feces.

    With some indoor flea infestations, the number of fleas emerging into the home increases substantially in the month after all pets are treated with a monthly flea control product.5,6 These are called redline homes, and in these cases, pet owners will see more fleas on their pets—and possibly themselves—than before treatment. When confronted with increasing numbers of fleas, pet owners inevitably conclude that the flea control product is not working at all. In fact, the fleas emerging into the home after the pets were treated came from eggs laid weeks before treatment. Those eggs will continue to develop into larvae, pupae, and adult fleas, and the pet owners will continue to see new fleas on their pets until all the adult fleas have emerged. Depending on the temperature, it can take 3 weeks to several months for the infestation to run its course.9–12

    Case Presentation: Fleas in a Flash!

    Signalment: A small, castrated, 4-year-old mixed-breed dog and a castrated, 13-year-old shepherd mix.

    Figure 1. Front yard. The owner had replaced the lawn with bark mulch.

    History: At the time of enrollment, the owner told the Flea Team that the dogs had always had a flea problem. The problem became so severe that in an effort to eliminate the fleas, theowner killed the grass in the front lawn and replaced it with bark mulch (FIGURE 1). Since then, she had sprayed her yard frequently with an insecticide, but the dogs still had fleas. After treatment with Frontline Plus, the dogs had fewer fleas, but the owner still found fleas on them every day (TABLE 1).

    Table 1. Questions Asked of the Owner



    How many hours a day does the pet spend outdoors? Where does it go: the backyard, shared courtyard, sidewalk, or dog parks?

    Both dogs go out frequently, but only to “use the yard.” They do not go outside the fenced-in yard.

    Do other pets visit your household, or does your pet visit another home?


    Where does your pet sleep or rest?

    The dogs sleep in the owner’s room and rest in the living room.

    Do you have an elevated porch, a crawl space, or another structure under which your pet, stray animals, or wildlife might go?


    Do you see feral cats, dogs, or wildlife in your yard or neighborhood?

    The owner sees opossums in the yard.

    Examination of the pets: Examination of the shepherd mix revealed just two fleas. The smaller dog (Ralph) had several fleas. The Flea Team combed all the fleas (21) off Ralph and took him outside to see where he might pick up new fleas.

    Figure 2. Ralph exits the makeshift shed next to the house. After spending no more than 10 seconds in the shed, Ralph had acquired four new fleas.

    Figure 3. After learning that Ralph acquired fleas from the shed, the owner thoroughly cleaned the area.

    Examination of the premises: After a couple minutes in the front yard, Ralph was scratching at himself and one flea was found. The dog then went into the backyard and ran into a covered shed between the house and a fence (FIGURE 2). Various yard items were stored in this area. Ralph stayed in the shed for about 10 seconds. When he ran out, Dr. Dryden caught him and found four new fleas crawling in his inguinal area. Two weeks later, the Flea Team returned and again combed fleas (12) off Ralph and let him into the yard. The owner had cleaned the shed and sprayed it with insecticide (FIGURE 3), and this time, when Ralph went into the shed, no new fleas jumped on him. However, when he went under the arborvitae trees (FIGURE 4) along the other side of the house to “use the yard,” he picked up two new fleas. The owner acknowledged that her other dog had recently cornered an opossum under the trees.

    Diagnosis: The source of the dog’s fleas was the backyard. Fleas were developing in sand in the covered shed and under the arborvitae trees. The source of flea eggs was suspected to be opossums.

    Figure 4. When Ralph went under the arborvitae trees to use the yard, he acquired new fleas.

    Conclusions and lessons learned: Dogs can pick up fleas “in a flash” when they go outdoors, even for just a brief time. Emerged fleas orient toward light, and when an animal (or human) walks in front of the light, the change in light triggers the fleas to jump in the direction to which they are oriented.13 The fleas may not have found a preferred host (or even an animal), but it is an instinctive reflex. Ralph picked up four new fleas in just seconds. These fleas emerged from pupae that had developed from eggs that fell off a flea-infested animal, probably an opossum. Opossums are excellent hosts for cat fleas (C. felis), and in many suburban areas, they are a primary source of outdoor flea infestations.14 The shed and the arborvitae trees provided excellent shelter for opossums, and the shaded, sandy soil under the shed and trees provided ideal conditions for flea development. The key lesson is that as long as opossums or other flea-infested animals, such as cats or raccoons, have access to a yard, dogs will continue to acquire new fleas when they go out into the yard. Another important lesson is that it was not necessary for the owner to destroy her yard. Fleas do not develop in sunny lawns because flea larvae can be killed by exposure to direct sunlight or drowned by rain. Cleaning the shed and sweeping out the sand was probably helpful because it may have made it less inviting for an animal to seek shelter and less hospitable to flea larvae development. Judicious weekly spraying of an approved yard insecticide can also help reduce flea numbers outside.


    Click here to take a quiz and see what you have learned!

    In next month’s case, “Where Are All These Fleas Coming From?”, you will learn why pet owners may see many fleas on their pet even when the flea control product they applied is working as it should.

    This information has been peer reviewed. It does not necessarily reflect the opinions of, nor constitute or imply endorsement or recommendation by, the Publisher or Editorial Board. The Publisher is not responsible for any data, opinions, or statements provided herein.

    © 2011 Merial Limited, Duluth, GA. All rights reserved. Sponsored by Merial.

    The study from which these cases were selected was funded by Merial Limited, Duluth, GA. Dr. Dryden is a professor at Kansas State University College of Veterinary Medicine, and he performs studies and consulting work for Merial Limited and other animal health companies. Dr. Carithers and Dr. Murray are employees of Merial Limited.


    1. Dryden MW. Evaluation of Certain Parameters in the Bionomics of Ctenocephalides felis felis (Bouché 1835) [master’s thesis]. West Lafayette, IN: Purdue University; 1988:115.  

    2. Dryden MW. Host association, on-host longevity and egg production of Ctenocephalides felis felis. Vet Parasitol 1989;34:117-122.  

    3. Dryden M, Gaafar S. Blood Consumption by the cat flea, Ctenocephalides felis felis (Siphonaptera: Pulicidae). J Med Entomol 1991;28(3):394-400.  

    4. Dryden MW, Broce AB. Integrated flea control for the 21st century. Compend Contin Educ Pract Vet 2002;24(1 suppl):36-39.  

    5. Chin A, Lunn P, Dryden M. Persistent flea infestations in dogs and cats controlled with monthly topical applications of fipronil and methoprene. Aust Vet Pract 2005;35(3):89-96.  

    6. Dryden MW. How you and your clients can win the flea control battle. Vet Med 2009;Mar (suppl):17-26.  

    7. Dryden M, Rust M. The cat flea: biology, ecology and control. Vet Parasitol 1994;52:1-19.  

    8. Rust M, Dryden M. The biology, ecology and management of the cat flea. Ann Rev Entomol 1997;42:451-473.  

    9. Dryden MW, Perez HR, Ulitchny DM. Control of fleas on pets and in homes by use of imidacloprid or lufenuron and a pyrethrin spray. JAVMA 1999;215(1):36-39.  

    10. Dryden MW, Denenberg TM, Bunch S. Control of fleas on naturally infested dogs and cats and in private residences with topical spot applications of fipronil or imidacloprid. Vet Parasitol 2000;93(1): 69-75.  

    11. Dryden M, Denenberg TM, Bunch S, et al. Control of fleas on dogs and cats and in private residences with the combination of oral lufenuron and nitenpyram. Vet Ther 2001;2:208-214.  

    12. Dryden MW, Burkindine T, Lewis L, et al. Efficacy of selamectin in controlling natural flea infestations on pets and in private residences in comparison with imidacloprid and fipronil. Proc Am Assoc Vet Parasitol Annu Meet 2001:34.  

    13. Dryden MW, Broce AB. Development of a trap for collecting newly emerged Ctenocephalides felis (Siphonaptera: Pulicidae) in homes. J Med Entomol 1993;30(5):901-906.  

    14. Dryden MW, Broce AB, Cawthra J, Gnad D. Urban wildlife as reservoirs of cat fleas, Ctenocephalides felis. Proc Am Assoc Vet Parasitol Annu Meet 1995:65.  

    References »

    NEXT: Focus on Nutrition: Quiz: Hand Feeding Orphaned Small Ruminants


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