Flea Biology and Control

Adult fleas are small, wingless critters with backward projecting spines on their flattened highly sclerotized (hard) body. All these characteristics are well suited for their ectoparasitic way of life. Of course, there would be no advantage in being large as the host could easily remove such a creature. Insect wings are generally most useful in either finding a mate, food or seeking a favorable environment and all these factors seem to be readily available on the flea’s host. The backwards-projecting spines make it more difficult for the host to scratch-out or remove an adult flea because the spines can readily lodge in hair or feathers. Of course, forward projecting spines would hinder the flea’s movement through the forest of hair of many hosts. The adult flea is flattened from side to side thus allowing it to easily move through the host. Finally, a heavy sclerotized or thick exoskeleton makes it more difficult for the host to kill adult fleas by scratching or biting.

Fleas have a limited sense of smell with small antennae concealed in grooves. However, they can readily detect carbon dioxide thus possibly explaining why fleas get so excited and jump wildly when coming in contact with breath. Depending on the species, fleas may or may not have eyes but even in the case of the former they are thought to have a poor sense of vision, which is limited to detecting changing pattern of light and shadows. Their bodies are covered by a variety of sensory hairs and spines that can detect the vibrations of other animals. As a result of these various structures fleas are well adapted for detecting a host using smell (CO2), vibrations and shadows. This ability was recently illustrated by an experiment conducted on rabbit fleas. Two hundred and seventy-five adult fleas were marked and randomly released in an 18,000 square foot enclosed field. Then three rabbits were released in the field. After a few days over half of the released fleas were found on the rabbits.

Flea Identification

Worldwide there are over 1,600 species of fleas while in the US there are a few hundred. Most species are somewhat host specific and this alone can be used to a degree for identification (rabbit fleas occur mainly on rabbits, mice fleas occur primarily on mice, etc.). Regardless of this large number some species are much more commonly encountered and of more economic importance than others. The following is meant to be a beginning source for the identification of some of the more common economic species. The main criteria that are used for species identification in fleas are the presence or absence and shape of the pronotal and genal combs (Figure 1), length of the labial palps, shape of the head and a few other minor morphological characteristics.

Figure 1. The head and thorax of a cat flea illustrating the teeth of the genal and pronotal combs. Images courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

Based on structural differences the fleas that are commonly encountered in the US fall into 3 groups, mainly those which possess a genal and pronotal comb, those that only have a pronotal comb and those that lack both types of combs. The following key can be used to identify many of the common fleas found in the US.

Fleas with a Genal and Pronotal Comb

The cat flea (Ctenocephalides felis) and the dog flea (Ctenocephalides canis) obviously belong to the same genus and are very similar in appearance. They can be distinguished from other common fleas by the presence of both genal and pronotal combs. The mouse flea and rabbit fleas share this characteristic and can be distinguished from the cat and dog flea later. The main characteristic that is used to distinguish a cat flea from dog fleas is that in the dog flea the first tooth on the genal comb is distinctly shorter than the second while in the cat fleas they are of equal length. (Figure 2).

With paper wasps the nest is a single layer that is suspended upside down by a short stalk. Around the home, paper wasp nests typically are found under eaves, along fences, or can be found attached either to trees or plants. Hornet and yellow jacket nests may exist above or below ground; their nests are much larger than those of paper wasps, and are constructed of many layers of cells that are surrounded by a capsule-like structure.

Cat Flea

Dog Flea

Figure 2. A comparison of the cat and do fleas. Note in the cat flea the first and second teeth on the genal combs are of equal length, while in the dog flea the first is significantly shorter than the second. Images courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

As previously mentioned the rabbit and mouse fleas also possess a genal and pronotal comb. The mouse flea can be distinguish from the above 2 fleas and the rabbit flea by the fact that it lacks eyes (Figure 3).

Figure 4. A mouse flea (Leptopsylla segnis). Distinguished by the presence of a genal and pronotal comb and absence of an eye.

As with the above 3 species, the rabbit flea possesses a genal and pronotal comb but the distinguishing characteristic is that the genal comb is almost vertical in the rabbit flea (Figure 54) as opposed to a horizontal position in the other 3 species. The teeth on the comb are blunt in the rabbit flea.

Figure 4. A rabbit flea with blunt teeth on a nearly vertical genal comb.

Common Fleas with Only a Pronotal Comb

The northern rat flea (Figure 5) and the ground squirrel flea possess only a pronotal comb. No image is available for the ground squirrel flea.

Figure 5. The northern rat flea, Nosopsyllus fasciatus, is distinguished by lacking a genal comb.

Common Fleas Lacking Both a Genal and Pronotal Comb.

The stick tight flea (Figure 6) is characterized by the absence of a genal and pronotal comb and presence of an angular head and contracted thoracic area.

Figure 6. Stick tight flea. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

The Oriental rat flea, Xenopsylla chelopis, (Figure 7) is characterized by the absence of a genal and pronotal comb, and the mesonotum is divided by a thickening and the ocular bristle inserted in front of the eyes.

Figure 7. Oriental rat flea. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

The human flea, Pulex irritant (Figure 8) is characterized by a lack of genal and pronotal combs, and no mesonutum division and the ocular bristle located below the eye.

Figure 8. Human flea. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

Flea Biology

Fleas are often found on birds and mammals with over 2,000-3,000 species occurring worldwide. Based on feeding habits, there are 3 main types of fleas. The first type does not attach to the host while feeding. These fleas are easily transmitted from one host to another and most belong in this category. The second type includes stationary females that are anchored by their mouthparts while feeding on the host. The third includes gravid females that develop under the host’s skin and maintain a breathing pore to the outside.

The life cycles of most common fleas found in the US are somewhat similar. The following is based on the most common flea found on pets, namely the cat flea, Ctenocephalides felis (Figure 2). As with most fleas in temperate areas of the world cat fleas infestations tend to be seasonal reaching peak population in the summer months and in the colder areas dropping to almost non-existent in the winter months. As with all insects the length of the life cycle and therefore rate of reproduction is directly proportional to prevailing temperatures. To a point the warmer the temperature the faster an insect completes its life cycle. Also outdoors colder temperatures and rain greatly increase the mortality rate of fleas. Of course if pets are confined to indoor conditions or someone live in warmer tropical areas flea season can be year around.

The flea spends most of its adult stage on the host. As with most fleas the cat flea has preferred hosts (dog and cats) but in the absence of these will find and feed on other warm-blooded animals, including humans.

The mouthparts of adult fleas are adapted for slicing the skin and siphoning blood. In order to produce eggs a female flea must have a daily blood meal. Once fed she typically deposit her eggs on the host but most will drop off, as they are relative dry. The eggs are relatively large for such small insects, about the size of a grain of salt or approximately 1/12th the size of the adult flee. They are oval and rounded on both ends. A female flea deposits several eggs a day but since they are long lived she is capable of producing 300 to 400 eggs during her lifetime. When an infested pet (such as a cat during fleas season) sleeps on a table or other surface and leaves, it almost looks as if someone has taken salt and pepper and sprinkled it on this surface. This is called the salt and pepper effect. Of course the salt is the fleas’ eggs and the pepper is the feces of the adult fleas.

Once deposited the eggs hatch in 2 to 12 days depending on prevailing temperatures. As previously discussed the warmer the prevailing temperature (to a point) the faster the eggs hatch. Optimum development for fleas typically occurs in locations protected from rainfall and sunlight with a relative humidity of at least 75% and temperatures between 70 to 90 F.

The flea larva is elongated, legless with a well-developed head capsule and elongated sparse hairs on the body. When disturbed they will characteristically flip in circles. The larval stage (Figure 9) is a scavenger feeding on any of a variety organic matter including dander, feces, food particles and other organic matter. One of main ingredients in their diet is the adult feces that is quite high in protein. Adult fleas bite and feed many more times than are needed to fulfill their nutritional requirements. As a result their feces is very high in partially or undigested blood. This is a very efficient system. As the host walks around it is not only dropping flea eggs into the environment but is also dropping the main ingredient of the larval diet.

Figure 9. The larval stage of a flea, a scavenger. Image courtesy of CDC Healthwise Photo Library.

The larval stage may be completed in as little as 9 days or under unfavorable conditions can be extended as long as 200. Larval development is normally restricted to protected places where there is at least 75% relative humidity. At the end of this active feeding stage after the larva has reached full growth, it spins a cocoon around its body and pupates. The pupal cocoon (Figure 10) typically is covered by bits of their environment including such materials as lint, hair, dirt and sand. Again the length development of the pupal stage is quit variable but at room temperature approaches 2 weeks.

Figure 10. The pupa in case

Pupa removed from case. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

Once fleas emerge from the pupae they remain in the silken cocoons until the presence of an approaching host trigger them out. Prior to emergence from the cocoon an adult flea can survive for an extended period of time (350 days or more). However, once emerged the adult must feed or it will die in a few days. If continuously fed some species can live for a year or more. The longest recorded life cycle of a flea is 996 days for Pulex irritans, the human flea.

Frequently Asked Questions

A few occurrences or questions homeowners commonly encounter or ask can be explained by flea biology.

Scenario #1. Prior to taking their German Shepard with them on a 4-week vacation, homeowners have a little problem with flea bites. They return to find dozens of fleas jumping all over their legs. Answer. Prior to leaving, most of the fleas that emerged from their pupae fed on the preferred host--the dog. While they were gone, many fleas completed their life cycle as the host presence was not necessary; the larvae are scavengers. Because no one was home, the adult fleas that emerged remained in their loose cocoons. Upon their return, the homeowners’ vibrations triggered the fleas out of their cocoons. Of course one solution would be to send the dog in first to collect all the waiting fleas (joke).

Scenario #2. Someone has a flea problem in their home but does not have any pets. In this case, there was probably a flea-ridden animal in or under the home at one time. Upon its departure the fleas were left to seek the only available host, the human. Possibly someone had spent a few days in the home with their pet dog or possibly there was a litter of kittens below the house. There may not be many fleas in the home with this type of situation, but those that are left will make their presence known and will bite the homeowner.

Question #1. I am frequently bitten by fleas and my wife is almost never attacked. Why? Answer. Blood feeding insects such as fleas and mosquitoes are attracted to their victim by chemicals such as those found in sweat and breath (CO2). People obviously smell different and are more or less attractive. Amazingly, there even seems to be a difference in attractiveness to individuals depending on the geographical area. We have noticed that mosquitoes are more attracted to my wife in Thailand but are more attracted to me in Central America. Individual sensitivity to bites is another factor, which can partially answer this dilemma. To some bites are extremely annoying while to others they are hardly noticed. The difference is due to an allergic reaction to the saliva that is injected when a flea feeds. There are different degrees of allergic reactions amongst different individuals. The function of the saliva is to keep blood flowing while the flea feeds. It contains an anticoagulant.

Question #2. I just moved into an apartment and there were hundreds of fleas. This is especially puzzling since it has been vacant for 2 months and it was treated for fleas when the previous tenant moved. Answer. The people who lived there before you probably had pets. The adult fleas you are seeing are those that have not emerged from their cocoons. Remember adult fleas can remain alive in this condition for up to 12 months or so. If the house was previously treated, treatment probably did not penetrate the carpet where these larvae and pupae were developing.

Question #3. I have bombed my house three times this month and still have a problem with fleas. Why? Insecticide bombs do not to penetrate and would not reach developing flea larvae and pupae deep in the rugs. If you did not treat your yard it is possible that new adult fleas could be coming into your house on you or your pet.

Questions #4. Why do fleas seem to be more of a problem in my beach house as opposed to my home in the inland valley? Answer. First of all part of the answer may be due to differences in climate. Temperatures at the beach tend to be milder and therefore favorable for flea development and survival than those in inland areas. Beach areas tend to also have a higher humidity, which is also favorable for flea development and survival. Finally people frequently confuse sand fleas with true fleas.

Question #5. What are sand fleas? "Sand fleas" or "beach fleas" are common names for small orange crustaceans called amphipods found along the beach. They are distant non-insect relatives of true fleas, and do not even bite. Also, some people may refer to fleas that just happen to be developing in sandy areas as "sand fleas".

Flea Disease and other Maladies

Fleas are common vectors of some very notorious diseases. The most well known worldwide disease is the Bubonic Plague (Figure 11). In the sixth and fourteenth century this disease swept the earth with hundred year plagues killing approximately 1/4 the population of Europe. The most recent epidemic of this disease was in Northern China at the turn of the 20th century. The plague is still present today and is mostly harbored in rodent populations (Sylvatic plague).

Figure 11. Worldwide distribution of plague. Image Courtesy of the Center for Disease Control and Prevention.

New Mexico has the highest incidence of the disease in the United States, especially in American Indian reservations. There are locations in California where plaque is known to periodically occur in the rodent populations. Some of these locations include Diamond Bar, Anaheim Hills, Griffith Park and Angeles Crest. The rodents in these areas (ground squirrels and voles) are closely monitored by the Health Department during the summer months for any signs of plaque. If found the situation is quickly corrected by rodent eradication and flea control. Through these efforts plague is kept in check in California and other states. Annually we average less than one human case of this disease in California (Figure 12).

Figure 12. Distribution of plague in the Western US by County. Image courtesy of The Center for Disease Control and Prevention.

The symptoms of the disease include a rapid onset, with an incubation period of only 2 to 10 days, a fever reaching up to 104oF, and flu-like nausea. In some cases, buboes (hence the name bubonic plague) form from swollen lymph nodes in the pelvic area, groin, armpits, and back of neck. The buboes form on the second day after symptoms appear and are very tender and sore. The disease can then progress to the blood (septicemia plague) system where the spleen and liver are affected. In the third stage, which is 90% lethal, the disease progresses to the respiratory tract (pneumonic plague)? This is an extremely contagious stage and can be transmitted through coughing. Handling of any wild animals should not be undertaken unless absolutely necessary. Veterinarians appear to be the group most at risk for contracting this disease.

Both male and female fleas transmit the disease while feeding. This occurs due to a plague bacterial buildup in the gut of the insect and subsequent regurgitation of the blockage by the flea into the host while feeding. Plague season typically occurs during the summer months. Apparently higher temperatures are necessary for a bacterial blockage to occur in the flea’s gut. Because of the blockage, the flea does not "feel" full and jumps from host to host in order to feed more. This, of course, spreads the disease even further. There is a vaccine available, but it is not recommended because of severe side effects. Currently, only military personnel are given this vaccine.

Murine Typhus (Rickettsia typhi) is another disease that fleas transmit and is usually found in rural areas. The fleas responsible for this disease are the same as those that vector plague. Antibiotics are effective when given at the first onset of symptoms.

With very heavy prolonged flea infestations pets can develop anemia. In extreme cases a pet may harbor an infestation of several hundred fleas. In such cases the animal’s immune system can be severely damaged resulting in death. Heavy infestations are more common in kittens and puppies as they are less proficient than adults in mechanically removing fleas by biting and scratching.

Pets may develop allergic reactions to flea bites. This is especially true in older pets, which have a long history of flea infestations. As with most allergic reactions the tendency to do so is genetically linked. It is not uncommon in households with many cats for a few to develop this type of allergies while others harboring approximately the same number of fleas are apparently unaffected. In cases of extreme allergic reactions the animal will loose large amounts of hair, especially around the rump and on the tail. One of our black cats (we call him old bald butt Bart) develops this condition every flea season. Once such an allergy develops the bite of a single flea can initiate the condition. In addition to hair lost the animal may develop reddened skin and small scabs over much of his or her body. The latter are partially due to the excessive scratching of the animal. Normally a veterinarian can be corrected allergic reactions by injection and oral administration of cortisones and flea control.

Fleas can serve as an intermediate host for dog and cat tapeworms. Fleas are typically infested with the cyst when the larvae feed on the feces of a tapeworm infested host. The cyst form is subsequently passed on to the adult flea. Consuming the adult flea can in turn infest a cat, dog or even small child. Once consumed the worm form emerges from the cyst and begins to feed in the digestive tract. Tapeworm feed by absorbing nutrients. This may result in loss of weight and a rundown condition in the host. An infestation is usually diagnosed by the presence of the crawling almost square worms that are about the size of a grain of rice in the feces of the host.

Common Fleas

The Oriental rat flea, Xenopsylla cheopis (Figure 13), and northern rat flea, Nosopsyllus fasciatus are the primary vectors of the plague. These fleas attack the Norway rat, roof rat, and black rat, all of which are commonly associated with humans. They also are typically found on ground squirrels, wood rats, and prairie dogs.

Figure 13. The Oriental rat flea. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

The 2 major fleas that are of household concern are the dog flea, Ctenocephalides canis, and the cat flea C. felis, respectively (Figure 2). Both of these are problematic for pets in the US, with some animals having severe allergic reactions. Typical symptoms of an allergic reaction to fleas in cats and dogs include a loss of hair, especially around the upper rump, flaky dry skin and many bumps and scratches due to the pet’s attempts to remove the fleas. Older animals are typically most susceptible. This is especially true if the animal has had a history of flea infestations. In some cases the bite of a single flea can result in these symptoms if the animal is highly allergic. Treatment for allergic reactions includes flea control and cortisone shots by a veterinarian.

Typically when these 2 species bite humans most bites occur around the lower legs (Figure 14). As with some other fleas when they bite they will feed many more than needed for nourishment. The bites shown on the above illustration are those from a few fleas (possibly one).

Figure 13. Typical cat flea bites occurring on lower legs. Image Courtesy of Vopak Inc.

The human flea, Pulex irritans (Figure 14), is found all over the world. Besides humans, it infests cats, dogs and many other animals, particularly pigs. It breeds profusely in pigsties, and people working in them can pick up large numbers of fleas and start infestations in their own homes. The human flea is usually the most important flea in farm areas; while the bite of cat fleas tends to be concentrated on the lower part of the legs, those of the human flea may be spread all over the body.

Figure 14. The human flea. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

The human flea is the species that was used in the 1800’s in European flea circuses. They were chosen for their exceptional ability to jump (over 6 inches high and 13 inches laterally) and supposed strength. They can pull over 400 time their own weight. They later fact is especially impressive since the average human cannot pull much over once their weight. In the circuses these fleas performed a variety of acrobatic stunts including pulling tiny carts through the streets of miniature villages. These circuses eventually became sideshows in fairs and informal outdoor markets. These events became known as flea markets, a term we are all familiar with today.

The sticktight flea, Echidnophaga gallinacea, is one of the smaller fleas with males measuring less than 1mm (Figure 15). The adult flea attaches itself on the head or neck of domestic fowl, sometimes causing ulcers. Females lay their eggs in the ulcers and the hatching larvae fall to the ground and feed on decaying plant material. Sticktight fleas can become quite abundant in poultry yards and adjacent building. Besides birds they can attack humans, rat, cats, dogs, and many other mammals. They are potential vectors of plague but their habit of remaining tightly to one host greatly reduces this possibility.

Figure 15. The adult of the sticktight flea, a poultry pest.

The chigoe, Tunga penetrans, (Figure 16) is also known as chiggers, jiggers, chique and sand fleas. Some of these latter names can be misleading, as these are neither true chiggers, which are of course mites nor true sand fleas, which are actually crustaceans. This is a tiny burrowing flea that is found in the tropical areas of North and South America, Africa and the West Indies. It is said to have inspired the sailor’s saying, “I’ll be jiggered”.

Figure 16. The adult chigoe, also known as a jigger or sand flea. Image courtesy of Department of Parasitology, University of Sao Paulo, Brazil.

An infestation of these fleas is referred to as tungiasis. Gonzalez Fernandez De Oviedo y Valdes noted the earliest report of tungiasis at the turn of the 16th Century when Spanish conquerors of the crew of the Santa Maria were shipwrecked on Haiti and became infested with the disease. A few years later, the Spanish conqueror Gonzalo Ximenes de Quesada reported an entire village in Colombia that had been abandoned by its inhabitants due to this disease. Consequently, his soldiers became so infected with the disease that they could barely walk. In the 17th Century, Aleixo de Abreu, a Portuguese physician working in the Brazilian government, provided the world with the first scientific description.

The sand flea is normally found in the sandy terrain of warm, dry climates. It prefers deserts, beaches, stables, stock farms, and the soil and dust close to farms. While both male and female sand fleas intermittently feed on their warm-blooded hosts, it is the pregnant female flea that burrows into the skin of the host and causes the cutaneous lesion. She does not have any specialized burrowing organs; rather, she simply attaches to the skin by her anchoring mouth and claws and burrows violently into the epidermis. Since this process is painless, it is thought that the flea may release some type of tissue dissolving enzymes. After penetrating she leaves her posterior (rear) end exposed (Figure 17). The "black dot" of the nodule is this posterior end of the flea sticking out. The opening provides the flea with air and an exit route for feces and eggs. With its head deep into the skin, the flea begins to feed on the host’s blood and enlarges up to 1cm in diameter. Over the next two weeks, over 100 eggs are released through the exposed opening and fall to the ground. The flea then dies and is slowly sloughed by the host’s skin. The eggs hatch on the ground in 3-4 days. In the next 3-4 weeks, they go through their larval and pupal stages and become adults. The complete life cycle of these fleas is about one month.

Figure 17. An adult chigoe buried into the skin.

The first evidence of infestation by this sand flea is a tiny black dot on the skin at the point of penetration. Because the flea is a poor jumper, most lesions occur on the feet (Figure 18), often on the soles, the toe webs, and around or under the toenails. Among natives who frequently squat, however, the buttocks and scrotal sac can be involved. A small, inflammatory papule with a central black dot forms early. Within the next few weeks, the papule slowly enlarges into a white, pea-sized nodule with well-defined borders between 4-10mm in diameter. This lesion can range from asymptomatic to pruritic to extremely painful. Multiple/severe infestations may result in a cluster of nodules with a honeycomb appearance. Heavy infestations may lead to severe inflammation, ulceration, and fibrosis. Lymphangitis, gangrene, sepsis, the loss of toenails, autoamputation of the toes, and death may also occur. In most cases, however, this lesion heals without further complications. Nonetheless, the risk of secondary infection is high. Tetanus is a common secondary infection that has reported associations with death. People should avoid walking with bare feet where these fleas are known to occur. Of course dogs and other pets are frequently infected (Figure 19).

Figure 18. Ulcers on the feet due to burrowing chigoe fleas. Image courtesy of Department of Parasitology, Sao Paulo, Brazil.

Figure 19. Ulcer on dog legs due to feeding of chigoe flea. Image courtesy of Department of Parasitology, Sao Paulo Brazil.

Flea Control

The cat flea is the most common flea found feeding on hosts such as domestic pets, humans, rodents, raccoons, and other wild animals. Successful flea control begins with identification of the species involved, determining the source of infestation and understanding the flea life cycle.

The first step is to interviews the building occupants concerning household practices and recent animal visitors. This will alert the professional as to hot spots and potential sources of the infestation. Next a thorough interior inspection should be made to determine the presence of fleas, concentrating on where domestic animals sleep or common avenues of travel. This can be accomplished by using a vacuum device, a white-sock test or a light trap, as well as inspecting domestic animals thoroughly. Finally a thorough exterior inspection should be performed, especially where domestic animals frequent or wild animals nest, such as under porches, crawl spaces, perimeter fence areas, kennel areas, and overgrown vegetation (shrubbery).

Successful control typically encompasses eradication of the fleas on the pet, in the home and in outdoor locations. Control on the pet alone is typically futile since the eggs, larvae and pupae are found off the host thus continually providing a source of new adult fleas for reinfestation.

Treatment of Pets

There are an infinite number of products and devices available for control of fleas on pets. Although the pest control operator typically does not (and should not) become directly involved in this aspect of flea control, it is to his or her advantage to be aware of the various means that are available for this purpose.

Flea combs. These devices are not very effective and when used properly will only remove 10 to 60% of the adult fleas. This method is also very time consuming.

Shampoos. These products tend to be a temporary solution to an on-going problem. One advantage is that they do not only kill adult fleas but also remove dried skin and fleas feces that eventually fall to the ground and serve as food for the flea larvae. Typically with flea shampoos the animal should be thoroughly lathered and rinsed after 15 minutes. There are a variety of products available containing different active ingredients. Pyrethrins are derived from Chrysanthemum flower heads. They kill adult fleas quickly but have essentially no residual activity or lasting effects. Pyrethroids are synthetically produced and have a longer residual activity. Carbaryl is a carbamate insecticide that has a long history in pest control. This material is somewhat toxic to cats so label instructions should be carefully followed. Citrus peel derivatives, such as D-limonene are used in some shampoo products, which are fairly mild making them useful for use on kittens and puppies as well as in household with new babies. However, in some cases cats may exhibit allergic reactions to these materials. Pennyroyal oil is another natural product used in pet shampoos. Pulegone, the active ingredient in this oil can be toxic to animals if misused resulting in any of a number of side effect including death due to liver failure. If used label directions should be followed carefully.

Topical Applications. Some of the newest products for flea control are imidactloprid (Advantage), fipronil (Frontline) and (Program). Advantage and Frontline are spot-on oils and are applies monthly as a small drop to the back of the neck to prevent removal by grooming. The products quickly spread over the body due to movement of the animal. They are nontoxic to mammals and kill most of the fleas on the animal within 24 hours. Advantage provides approximately 98% control for the first 3 week on dogs and cats. Control drops slightly during the 4 week. Frontline provides a somewhat longer residual activity with a 98% kill for up to 8 and 6 weeks on dogs and cats, respectively.

Lufenuron (Program) attacks the problem from a different perspective than Advantage or Frontline. The active ingredient in this product is a chitin inhibitor. Chitin is the main protein in the insect’s exoskeleton that gives it strength. As with the other above-mentioned products Program is usually applied on a monthly basis. It does not kill the adult fleas but once the fleas feed on the treated pet the active ingredient prevents chitin from forming in the flea’s eggs. As a result when the eggs are produced they break due to the lack of chitin in the shell. In order to be effective Program must be used immediately prior and during the entire flea season. The idea is to prevent the flea infestations from developing in the first place.

Flea collars. Most studies indicate that flea collars are relative ineffective when compared to many other available means of control. This is especially true when ultrasonic flea collars are concerned. These devices have been found to have no significant effect on fleas.

Control in the Home and Yard

It is worthwhile to discuss with family members the areas in and around the home where pets spend most of their time sleeping and resting. Hot spots of activity can be determined by placing white socks over shoes and walking throughout the residence. Hot spots in homes with dogs are usually areas where the animals go in and out of the home, eat, sleep and spend time with the family. Cats frequent similar areas but should include high areas including tops of refrigerators, cabinets and bookcases. There are commercially available flea traps (Happy Jack and pulvex), which can be useful for monitoring flea populations. Research indicates that the larva do not move far from the site of hatching, especially if food is available.


Sanitation is one of the first steps to effective flea management in the home. Vacuuming on a regular basis (a minimum of every other day) will remove many of the various stages, dried blood and other sources of larval food from the carpet or areas where the pets sleep. Prior to any pesticide application the carpet should be vacuumed thoroughly with a beater-bar type vacuum. This will open up the carpets nap to allow treatment to reach deeper into the carpet where much of the infestation occurs. Research indicates that approximately 83% of the larvae spend most of their time deep in the carpet at the base of the fiber. At pupation the larvae move up the carpet fiber spinning a camouflaging cocoon around itself. Vacuuming is especially important where lint and pet hairs accumulate along baseboards, around carpet edges, on ventilators, around floor heaters, in floor cracks and under and in furniture where pets sleep. After vacuuming, the vacuum bags should be discarded in an outdoor trash container. Thorough vacuuming can be an effective tool in a flea pest management system. All pet bedding should be thoroughly washed on a regular basis.

Trimming lawns and weeds will create a drier, less-ideal environment for flea larvae. It can also be beneficial to avoid piles of sand and gravel around the home. Dogs should be prevented from roaming freely in and outside the yard, especially in heavily weeded areas or other areas where they may encounter reinfesting fleas. Areas that are difficult to access such as crawl spaces or attics under a home should be sealed to prevent pet entry. A crawl space is an ideal location for fleas to breed. It is also important to eliminate possible infestations of wild animals such as raccoons, opossum rats and birds near the premises.

Chemical Control

Even though much of the above can useful in preventing and reducing flea infestations in the home chemical control is the ultimate weapon. There are dozens of chemicals registered for flea control and a discussion of all these are beyond the scope of this manuscript. We have tried to include those that are most commonly used and are not in the business of recommending any.

Before treating, the homeowner should remove all toys and pillows off the floor or carpet, from under beds and furniture and on closet floors. All areas frequented by pets (e.g. table tops, refrigerator tops, window sills, counter, etc.) should be thoroughly cleaned. All pets should be removed from the premises prior to treatment. This would include covering aquariums.

Insect Growth Regulators (IGRs). This is a relatively new group of chemicals with a totally different mode of action than the so called conventional insecticides. Although the growth regulators do eventually kill their primary function is to disrupt the growth and molting process. In most cases this results in malformed insects that cannot function properly. In order to understand how these products work a brief description of the function of the hormones that control growth and molting in insects is needed.

Hormones are chemical substances that are introduced into the blood and subsequently to other parts of the body where they produce some effect on physiological processes. In insects there are 3 glands that secrete hormones that regulate growth and molting. These are the brain hormone, ecdysone and the juvenile hormone

The brain hormone, which is secreted by a gland at the base of the brain, plays an important role in molting by stimulating a pair of glands in the prothorax to produce a second hormone called ecdysone or the molting hormone. Ecdysone functions to control when molting occurs and the rate of growth of insects. The third hormone, juvenile hormone or JH is secreted by another gland in the brain and functions to determine what an insect will molt into. If there is a high level of juvenile hormone during the molting process the insect will stay in a juvenile stage-e.g.-larva to larva, nymph to nymph. If there is a low level the insect will advance in stage.

Scientists have chemically identified some of these hormones in key insects. Once the chemical structure of a hormone is known it can be synthetically produced in the laboratory. It turns out that if abnormal amounts of a synthetically produced hormone are applied to an insect then abnormal molts occur. In some cases monstrous, deformed insects occur (e.g.-half larva half pupa). There hasn’t been much done with the brain hormone. It typically has too complex of a molecule, which makes it too hard to identify or synthetically produce in the laboratory. Ecdysone typically has a steroid component to its molecule. Since humans also have steroids in their bodies this might makes it difficult to get these types of chemicals registered as a useable pesticide with the EPA.

The juvenile hormone is the main chemical that has been used as an insecticide. Actually the juvenile hormone mimics that are used do not have the same chemical structure as what occurs naturally in the insect’s body. The main reason is that a natural occurring chemical cannot be patented. As a consequence the chemical companies that produce these pesticides change the chemical structure a little when they synthetically produced them in order to patent the compound and protect their investments. As a group the juvenile hormone mimics are referred to as Insect Growth Regulators.

There are currently a few of these chemicals that are registered for flea control. One of the disadvantages of some of the IGRs (for outdoor use) is that they tend to breakdown when exposed to sunlight. However, a recent study using pyriproxfen (Nylar) reported it to be stable in sunlight when used outdoors for three weeks. In this study it gave 90% control of developing fleas. Methoprene (Precor) is reportedly another effective IGR for flea control.

A disadvantage of these types of chemical is that they do not kill adult insects which of course do not molt. As a consequence an adulticide is also mixed in the spray tank when using IGRs.

Other Chemicals

One of the more commonly used and effective indoor flea sprays is a combination of Precor and Catalyst or Safrotin. Also a coarse spray (40psi) of diazinon (Knox Out 2 FM), resmethrin (Vectrin), applied to cracks and crevices of floors, molding and baseboards are said to give good results. Other flea killers include tetramethrin (Bio Flea Halt), amorphous silica gel (Drione, Tri-Die), bendiocarb, (Ficam) and diatomaceous earth (Answer, Organic Plus). Chemicals more commonly used by pest control operators include Ficam +, Cynoff, Tempo, Delta Guard and Suspend. Water-soluble sprays are generally used for treating all carpeting and upholstered furniture. The operator should always read and follow the label directions closely. If followed correctly potential problems can be greatly eliminated.

If the pets spend any time outdoor treatment of the yard is needed. When doing so the preferred breeding locations, areas where the animals spend most of their time and biology of the fleas should be considered. Again outdoors fleas typically breed in shaded, moist but not wet locations. Keeping this in mind it does little good and is a waste of time and money to treat the whole yard. Cats using sand boxes and dogs sleeping under shrubs or in crawls spaces or garages provide a reservoir for fleas. Animal pens, kennels, doghouses, sandy soil and gravel driveway are other important sources to consider. Clean and sweep porches, mow lawns and soak dry soil with water before treating to bring flea larvae up to the surface. Commonly used insecticides for outdoors treatment include fenvalerate, carbaryl, diazinon, popoxur, resmethrin, Knox Out and bendiocarb.