Fall Fleas: The Itchy Facts

August 2006 - by Doctor Denise E. Roche, DVM  

Ctenocephalides felis – the cat flea- is the most common species of flea to infest our pets. September seems to be the time of year when flea infestations are at their worst.  Once you notice fleas on your pet, successful flea control involves two parts. First you must eliminate fleas from your pet and second you must control fleas in the environment. In order to effectively control fleas, it is important to understand the flea’s life cycle and how a flea infestation occurs. Often times the environment is overlooked because we don’t see fleas in our surroundings – we only see fleas on our pets.

Think of fleas as having a life cycle similar to that of butterflies. Each has a four-stage life cycle.  With butterflies, there is an adult that lays eggs that hatch into caterpillars and then become pupae in a cocoon from which a beautiful butterfly emerges.  Similarly, an adult flea lays eggs that become larvae (the caterpillar) that in turn become pupae in a cocoon before hatching out into young adult fleas.  The adult fleas that we see make up about 5% of an infestation.  The other 95 % of the fleas are developing in the environment and go virtually unnoticed. (Are you itching yet??)

The Egg Stage:

Eggs make up about 50% of an infestation. Eggs are about the size of a grain of salt. A female flea lays from 20 to 50 eggs per day which translates up to 2000 eggs in her lifetime. A female flea lays her eggs in the pet’s haircoat. Since the eggs are not sticky, they slip off the haircoat into the environment. Thus, flea eggs can be deposited in all the places that your pet has access. Eggs usually hatch in 1 to 10 days depending on temperature and humidity.  Humidity needs to be over 50% to prevent flea eggs from drying out and dying.

The Larval Stage:

Larvae make up about 35% of an infestation. Larvae are about an 1/8th of an inch in length. Larvae emerge from the flea eggs and begin feeding on organic debris and adult flea feces in their environment.  Larvae are free moving and can crawl as far as 20 feet.  Larvae are photophobic (light avoiding) and go deep into carpet fibers, mattresses, and furniture cushions. Larvae are usually not found in open areas or in area devoid of debris such as tile or wood floors. Moisture in the environment is essential for development and a relative humidity less than 50% will cause desiccation. The larval stage lasts 5 to 11 days. The transition from egg to larvae and larvae to pupae is regulated by a juvenile hormone.  When this hormone drops, the molting process can begin.

The Pupal Stage:

The pupal stage makes up 10% of an infestation. The mature larva produces a silken cocoon.  The cocoon is sticky and it is easily camouflaged with environmental debris.  Within the cocoon, the pupae become pre-emerged adult fleas. Pupae can become adult fleas in as quick as 5 to 10 days.  Or these pre-emerged adult fleas can survive in their protective cocoons for up to 9 months. Physical pressure (a pet or person’s steps), vibration (walking movements or vacuuming) carbon dioxide (exhaled from a mammalian host) and heat can all stimulate emergence from the cocoon. Flea pupae do not hatch all at once regardless of the stimuli. There is an unknown communication between the flea pupae that causes emergence to be staggered over time. This is to increase the likelihood of survival of the fleas. Thus, small numbers of fleas may continue to emerge for up to a year.  However, most emergence occurs within 2 to 4 weeks. This staggered hatching is called the pupal window and is sometimes perceived as a flea control product failure.  Actually it is not.  Please note that during this time, the pupae are safely protected in the cocoon and therefore resistant to any environmental insecticides.   

Adult Stage:

The adult stage accounts for only 5% of the infestation.  Under ideal temperature and humidity, the entire life cycle from egg to adult flea can be completed in 14 to 28 days. An adult flea can emerge from a pupal cocoon, jump onto the pet host and begin feeding in as little as 7 seconds. The adult flea is a permanent parasite and does not leave its host unless it is forced off by an animal’s grooming behavior, insecticide induced death or natural death.  The adult flea can survive as long as 4 months.

After all of that, it is easy to see how an infestation can take hold and become overwhelming in only 2 to 4 weeks.  Obviously, it is best to prevent rather than treat a flea infestation.  The best preventives are the newer, once a month preventives that are applied topically to the skin.  Frontline is our favorite topical flea control for dogs and Revolution is our favorite topical flea control for cats. Although expensive, both of these products are extremely effective and very safe and worth the additional cost. Using them monthly year round is the best insurance against fleas.

If you already have an active infestation, remember that these topical once a month treatments kill the adult fleas which make up only 5% of the total flea population in your home.  Use an environmental spray that contains an IGR (insect growth regulator) that will help arrest the development of the flea eggs and larvae. By mimicking the juvenile hormone, IGRs will stall the development of eggs and larvae.  Flea larvae prefer warm, dark, moist, low light environments (seasonal Fall weather). Concentrate on these areas with your IGR spray.  Be sure to vacuum prior to any indoor treatment to stimulate the pupae to hatch from their cocoons so that the newly emerged fleas will be susceptible to the effects of the spray.  Retreat your environment two weeks later to catch the pupal window.  Also, watch for tapeworms on your pets since fleas act as vectors for tapeworms. Tapeworms may not be evident for several months following a flea infestation. Call us with any questions that you may have concerning fleas or tapeworms. 

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