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Fleas are bloodsucking insects that attack all kinds of domestic and wild mammals and birds. They are the most common and important external parasites of dogs and cats worldwide. It is very likely that dogs or cats get fleas sometime during their life, wherever they live. And as everybody knows, if a pet gets fleas, its owner will most likely get them as well. For solving flea problems or to prevent them it is very useful to know how fleas live and reproduce.

In this site there is also a specific article on fleas on livestock and their control.

Flea species on dogs and cats

Head of an adult female cat flea. Arrow points to typical comb = ctenidiumFleas of cats and dogs belong to the insect order called Siphonaptera. Worldwide there are more than 2000 species that attack pets, livestock, humans and also wild animals and birds.

The most common species on dogs and cats are the following, which have a rather similar biology and appear frequently as mixed infestations, whereby C. felis ist usually the most abundant one:

  • Ctenocephalides felis, the cat flea, the most frequent species in Europe and the Americas. It infests dogs and cats, as well as humans, livestock, and many other mammals (e.g. foxes, rodents, rabbits, squirrels) and birds, including chicken. It is the flea species mot common in humans as well.
  • Ctenocephalides canis, the dog flea, very similar to the cat flea but less frequent.
  • Pulex irritans, the human flea, which can also infest many domestic and wild animals, especially pigs.

Other important flea species than can also infest pets and humans are the following:

  • Xenopsylla cheopis, the tropical or oriental or rat flea, which attacks rats and other rodents and is the most effective transmitter (vector) of bubonic plague, a human disease casued by the bacterium Yersinia pestis. It can attack humans and other animals.
  • Echidnophaga gallinacea, the hen flea, the sticktight flea, attacks mainly chicken and other birds, but also rodents, rabbits, dogs, cats, foxes, and occasionally horses as well. Pregnant females remain firmly attached to the host, with the head incrusted in the skin and causing ulcers, typically building clusters in bare parts, e.g. around the eyes, the com, the wattles. On dogs and cats they may congregate on the ears or between the toe pads.
  • Tunga penetrans (=Sarcopsylla penetrans) the chigoe flea or jigger, is a tropical flea native to Central and South America, which occurs also in Africa and Asia. Infections with this flea are called tungiasis. It attacks dogs and cats, but also humans, livestock and other animals. It is one of the smallest fleas, not longer than 1 mm. Pregnant female fleas burrow into the skin, typically between the toes where they can cause intense itching and irritation. They cause up to 1 cm swellings with an opening for egg laying and defecation. Larvae develop preferably in dry and sandy soil. Development to adult fleas takes three to four weeks.

In the following chapters (anatomy, life-cycle, control, etc.) focus is on cat fleas (Ctenocephalides felis), the best investigated and most frequent species on pets.

Anatomy of cat and dog fleas

Legs of a cat flea with hairs, spines and clawsIf you are not familiar with the general biology of insects click here

Adult fleas are obligate bloodsucking insects (hematophagous), i.e. they cannot survive or reproduce without blood. They have no wings, are 1 to 2 mm long and have a dark reddish-brown color. Their body is laterally flattened for easier moving in the host's hair coat.

As in all insects, the body of fleas is divided in three parts: head, thorax and abdomen. The head carries the eyes, the antenna, the piercing mouthparts, and often a kind of comb called ctenidium made of an array of spicules. Some species have more than on such comb. The 3 pairs of legs inserted in the thorax end each with a claw for better holding on to the hosts' hairs or feathers. The abdomen has usually 10 segments and includes the genital organs.

Adult fleas are extraordinary jumpers. They can jump vertically up to about 20 cm and horizontally up to about 35 cm, which is more 100 to 200 times their size. For a human this would mean jumping over a 70 story building or over 3 soccer fields!

As in all insects, the body of fleas is covered by a hard external structure called the exoskeleton, which protects the internal organs from mechanical pressure and pathogens. It also serves as anchor for the muscles. The exoskeleton includes a cuticle, which contains chitin, a substance specific for insects, other arthropods (e.g. spiders, ticks, crustaceans, etc.) and fungi. Chitin is a complex polymer of N-acetylglucosamine, a sugar derivative, which is synthesized in the skin cells and is responsible for the toughness of the exoskeleton, while being quite flexible. The cuticle of fleas is particularly tough and covered with many hairs and spines that help the fleas to move inside the host's hair coat.

Life cycle and behavior of dog and cat fleas

Fleas undergo a complete metamorphosis (i.e. they are holometabolic) that includes 4 developmental stages: egg, larva (stages I, II and II), pupa (or cocoon), and adult (also called imago).

Flea eggs

Eggs (yellow arrow) and feces (red arrow) of cat fleas (Ctenocephalides felis)After hatching, adult females start laying eggs 24 to 26 hours after their first blood meal. A single female lays an daily average of 25 eggs during 50 days, but she can continue laying eggs for longer than 100 days. This means that a single flea can lay up to 2000 eggs in her lifetime. However, host grooming usually kills many adult fleas before they have started oviposition, which reduces such a high reproductive potential.

Cat flea eggs are about 0.5 mm long, and of a whitish color. Females lay the eggs in the host's hair coat, but they easily fall to the ground. Obviously, eggs will be more numerous wherever the pets use to sleep or rest for longer periods of time.

Eggs hatch 1 to 10 days after oviposition, depending on temperature and humidity. The warmer and hotter, the faster the hatching. Most eggs do not survive below 50% humidity.

Flea larvae

Newly hatched (stage I) larvae move freely in their environment. They are 1 to 2 mm long, of a white color, and have 13 segments. They grow and molt twice until reaching maturity. After each molt they leave the old skin (called exuvia). Molting is regulated by two hormones: ecdysone and juvenile hormone. A high level of juvenile hormone inhibits metamorphosis, whereas a high level of ecdysone favors molting. Mature larvae are 4 to 5 mm long.

Mature larva (stage III) of the cat flea (Ctenocephalides felis)The larval stage lasts 4 to 11 days, strongly depending on temperature, humidity and availability of food. Flea larvae feed on feces of the adult fleas, which consist mainly in incompletely digested blood. They also feed on other flea eggs, old skins (exuvia) and also other larvae, i.e., they are cannibalistic.

Flea larvae tend to crawl downwards (positive geotaxis) and prefer darker places. They crawl deeply into carpets and rugs, inside mattresses and upholstery, in cracks and crevices in the soil filled with organic material, below plant debris in gardens and lawns, etc. There they find the appropriate microclimate: moderate temperature and high humidity. Flea larvae can survive outdoors (gardens, lawns, backyards, barns, stables, etc.) but the most adequate environment is usually indoors.

Most larvae do not crawl more than 10 to 20 cm beyond the place where the eggs hatched. This means that they they are particularly numerous in those places the pets prefer for sleeping and resting.

Flea pupae (cocoon)

Cat flea (Ctenocephalides felis) cocoons covered with sandy dirtMature larvae stop feeding and crawling, spin a protective silk cocoon and develop to pupae inside the cocoon. Cocoons have an oval form and are of a whiitsh color. They are 0.5 mm long and have sticky silk fibers. The dirt and soil particles of the immediate environment stick to those fibers perfectly camouflaging the cocoon in its environment and thus protecting it from potential predators (e.g. ants).

Pupae do neither feed nor move. This means that they concentrate in the same places as eggs and larvae, i.e. in carpets, rugs, mattresses, upholstery, below furniture, pet's nests and cradles, etc.

Flea pupae are very resistant to dryness, but they do not survive long periods below 5°C or above 35° C. Most insecticides are not capable of penetrating inside the cocoon.

Development to adult fleas inside the cocoon is completed in 5 to 10 days. However, newly formed adults do not hatch immediately but remain inside for up to six months as preemerged adults, waiting to hatch at the right moment.

Adult fleas (imagos)

Preemerged adults remain inside the cocoon and do not hatch until they perceive signals that a suitable host is around: body heat, step pressure, carbon dioxide (exhaled by the host), etc. Vacuuming also simulates flea hatching. This behavior reduces the risk for hatching and starving in absence of suitable hosts. In addition, as long as preemerged flea remains inside the cocoon it remains protected from predators. Preemerged adults are also more resistant to extreme temperatures and dryness than hatched adults.

Within a flea population, e.g. in an apartment, in a barn, etc., adults usually do not hatch suddenly altogether, but temporarily staggered, i.e. they hatch in groups, first one group, later another one, and so on, partly ignoring the previously mentioned signals of the presence of suitable hosts. It is thought that there could be a kind of communication between pupae. This staggered hatching is called the pupal window effect.

Cat fleas (Ctenocephalides felis): adult female (left) and male (right)

All these factors increase the survival chances of flea populations and makes it more difficult to control them.

Newly emerged unfed fleas are especially aggressive and are attracted by several stimulants produced by potential hosts, especially body heat, exhaled carbon dioxide and movements. They are also attracted by light (in contrast with the larvae), especially intermittent light. And they are negatively geotactic, i.e. they move upwards, not downwards as larvae. This is why newly emerged adult fleas move to the surface of carpets, rugs, vegetation, etc., where suitable hosts are likely to be.

When a host comes near enough, hungry fleas just jump on it and move around in the hair coat searching for a suitable place to bite and suck blood. Once a flea has found a suitable host, usually it does not leave it unless it is forced to. This means that the fleas the re-infect a pet come mostly from the pet's environment and not from contact with another pet infested with fleas, although this can happen as well.

Flea populations

If an owner discovers fleas on his pet, it is very likely that a flea population has become established in the pet's environment, i.e. in the household. The structure of average flea populations looks like a pyramid with four floors. The first floor are the eggs, which represent about 50% of the population. Larvae make about 35% of the population and are the second floor. Pupae are about 10% of the population in the third floor. And adults in the top floor are only 5% of the population. This means that 95% of the fleas are not on the pets, but in the environment, waiting for a host to pass by or to complete development.

Therefore keep in mind that solving a flea problem means not only controlling adult fleas on the pet, but requires controlling the whole flea population in the household, not only the fleas on the pets.

These numbers reflect the fact that many eggs and larvae do not survive because they are predated by natural enemies (e.g. ants) or fellow larvae that are cannibalistic, because they do not find a suitable environment, because thy do not find food, etc.

In countries with moderate climate and cold winters, fleas overwinter as adults in domestic or wild animals, but also indoors as preemerged adults in adequate microclimates.

Harm to dogs and cats caused by fleas

It is estimated that flea-related diseases represent more than 50% of the dermatological cases reported by veterinarians, and close to 35% of their effort.

During their blood meals fleas inject saliva into the wound to prevent the blood from clogging. Flea saliva contains irritant substances that cause the typical itching. As it happens to human beings, whereas some pets are quite tolerant to flea bites and are not or only slightly annoyed, other pets can be very sensitive.

Some pets can become hypersensitive to flea saliva and react intensively to flea bites with typical allergic reactions such as appearance of skin redness (erythema), bumps (papules), scabs (crusts), hair loss, etc. Dogs are especially affected on the neck, ears, lower back, thighs and the tailhead. This condition is called Flea Allergy Dermatitis (FAD). Severe FAD cases can lead to self-mutilation due to exacerbated scratching and grooming. DAP can develop without proportion to the number of fleas. In extreme cases a single flea can already cause FAD in a hypersensitive pet. FAD can be alleviated with anti-allergic medicines, but a long-term solution requires adequately protecting the pet against fleas.

Severe flea infestations can also cause iron deficiency anemia due to blood loss.

Diseases transmitted to pets by fleas

Fleas are also transmitters (vectors) of various human and pet diseases and parasites.

The oriental rat flea, Xenopsylla cheopis, is the primary vector of typhus caused by Rickettsia typhii, but it has been demonstrated that the cat flea, Ctenocephalides felis, can also act as vectors of this disease.

The bacterium responsible for bubonic pest, Yersinia pestis, is also transmitted by Xenopsylla cheopis, the oriental rat flea, but other species can occasionally transmit this disease as well, including the cat flea, Ctenocephalides felis. However, bubonic pest is nowadays a rather infrequent disease.

The cat flea (Ctenocephalides felis), the dog flea (Ctenocephalides canis), and the human flea (Pulex irritans) can all three transmit Dipylidium caninum, the double-pored dog tapeworm that infests dogs and cats, and occasionally children. Flea larvae eat the eggs of the tapeworm, which develop to infective stages (cysticercus) inside the larvae. Dogs and cats ingest infected fleas while grooming and become themselves infected.

Flea control and prevention: strategic considerations

The most important thing to know about flea control is that a flea problem is almost always a flea population problem!!!

Nowadays a full arsenal of highly effective flea control products is available to pet owners. There are even too many, often with significant differences regarding efficacy, length of protection, spectrum of activity (i.e. whether they control other parasites such as ticks, mites, lice, worms, etc. or not), price, safety, etc. As a consequence it can be difficult for pet owners to find out which ones fit better to their needs. And such products have to be used correctly.

Knowing that 95% of the flea population is not on the pets but in the environment, and that population control is a key to successful flea control, it must be said that using a particular product may not be enough to solve the problem: a combination of chemical with non-chemical control tools may be required.

Which control tools are indicated depend a lot on important objective factors that influence the flea problem, e.g.:

  • Seasonality: seasonal occurrence (e.g. in moderate climates with cold winters) vs. year-round occurrence (e.g. in most tropical and subtropical regions)
  • Location: e.g. urban vs. rural environment.
  • Household type: e.g. single pet vs. multi pet households
  • Re-infestation risk: e.g. frequent vs. infrequent contact with other potentially infested pets or wildlife
  • Annoyance level for pets and humans. e.g. pets affected by Flea Allergy Dermatitis (FAD) or not.

Personal preferences, i.e. subjective factors that are independent from the flea problem itself but also important when choosing a control tool, e.g.:

  • Wish to keep humans (e.g. children) unexposed to chemicals
  • Out-of pocket cost of flea control
  • Willingness to invest time in understanding and managing the flea problem.
  • etc.

In a place with a cold winter (e.g. in the Northern United States, Canada, most of Europe, etc.) the flea problem "disappears" during the winter months. Correctly speaking, only the adult fleas disappear, all other stages remain in place waiting for the next warm season, but immature stages do not bite. This means that the problem does not disappear, it just takes a break. In this cases, it is highly advisable to start preventive treatments before the real problem starts again in the next season, i.e. before any signs of fleas have been noticed. Remember: "no adult fleas" does not mean "no fleas"!

If a pet catches occasionally 2 or 3 fleas, the owner will probably not notice it. These few fleas won't leave the pet to jump onto the owner and bite him. Consequently the perception is that "there is no flea problem". However, if the eggs produced by these fleas find a suitable environment, a problem can quickly develop.

If a pet owner perceives a "flea problem", this means most frequently that he/she or someone else in the household has been already bitten. And this means almost always that either the pets carry too many fleas and a few ones look for a new prey; or that many fleas are hatching out of cocoons in the environment and will jump onto anything that is warm and moves around. Or both things together: pets carry many fleas, and more are breeding in the environment: there is already a "flea population problem".

To face a flea problem, a key question is to estimate the size of the flea population. A sporadic flea infestation of a pet in a cold place, if quickly discovered can be often solved with a few treatments of the affected pet, because those fleas won't have time to lay too many eggs and infest the whole environment. But controlling a well established flea population in a household in a tropical region requires mostly continuous and consequent flea control and preventative measures.

As a thumb rule, if your or another person in the household is regularly bitten by fleas, there is definitely a flea population problem in the household that requires immediate action. If no person is bitten, but the pet is seen to scratch here and then, there may not be a population problem yet, but it is likely to develop if you do nothing.

Non-chemical prevention and control measures against dog and cat fleas

Indoor cleanness: cradles, nests and other places pets prefer

If pets have fleas, wherever they sleep or rest there will be a substantial accumulation of immature stages together with abundant food for the larvae (mainly flea feces) and at an ideal temperature. For this reason sanitation of these places is essential for flea prevention. They have to be cleaned or changed regularly, and stuffing materials, pieces of cloth, rags, etc. should be renewed or washed at high temperature to eliminate or kill whatever eggs, larvae or cocoons they may contain.

The same applies to any other places where pets like to stay: chairs, couches, cushions, beds (including blankets, mattresses, etc.), pillows, as well as whatever indoor or outdoor spots (yard, garden, balcony, stairs, etc.). These are the places where eggs, larvae and cocoons will accumulate, especially if they are covered with whatever thick textile. These places have to be vacuumed and/or steam cleaned frequently (e.g. weekly). Newest research indicates that vacuuming kills the fleas, thus immediate disposal of the dust bags is not necessary. It may be advisable to prevent pets from staying in places that are difficult to clean.

General hygiene and sanitation are always a good idea, but unremoved kitchen garbage or general trash are not a direct source of fleas, although they can certainly feed and/or breed numberless flies and cockroaches. However, such garbage can be an indirect source of fleas by attracting rodents (rats, mice) or birds, which are almost always infected with fleas.

Outdoor cleanness: gardens, yards, balconies, etc.

Fleas can also develop outdoors, in private and public grounds, especially in regions with warm and humid climate. A few measures can reduce their suitability for flea development.

  • Regular mowing the lawn. If grass becomes tall it will flourish and produce seeds. These seeds attract wild rodents and birds, which are almost always infected with fleas. And such small animals will attract straying dogs, cats, foxes and other hunters, which can carry even more fleas.
  • Remove whatever organic dirt and waste that could also attract small animals infected with fleas.
  • Keep domestic or wild animals off your property with walls or adequate fencing. Foxes, raccoons, skunks, hedgehogs, etc. can carry a lot of fleas.

Prefer hard flooring to carpets and rugs

There are structural measures that make the environment more or less appropriate for the development of flea eggs, larvae and cocoons, i.e. that are favorable or not for the establishment of a flea population.

  • Carpets and rugs (of natural or synthetic fibers) as well as dry sandy soils are ideal flea breeding environments. An option to reduce flea breeding can be to deploy carpets and rugs in winter, and to remove them in spring and summer.
  • Hard and plastic flooring (stone, tiles, wooden parquet, etc.) are much less appropriate for flea breading. However, gaps or cracks (e.g. between parquet slates) filled with dirt can support flea development.
  • Textile upholstery (natural or synthetic) are much more supportive of flea development than leather or plastic, which are impenetrable for the larvae: they will remain outside and dry out or starve.

Keep pets away from other animals that can have fleas

During the flea season it is especially important to prevent pets from getting in close contact with other pets that are likely to carry fleas, especially stray pets. 

There are many other animals that may have fleas and can transmit them to pets: squirrels, rats, mice, rabbits, guinea pigs, foxes, all kinds of birds, but also sheep, goats, cattle, horses, etc. If contact or close vicinity is not always avoidable, they should be kept off their habitats or stables.

Mechanical control of fleas on dogs and cats

As a general rule, mechanical contorl of fleas can reduce the flea numbers but are insufficient to solve a well established flea problem.

  • Flea combs, although cumbersome, can reduce the number of fleas on a pet by up to 75%. Obviously they don't eliminate any of the immature fleas in the environment.
  • Sticky traps and light traps can catch a lot of newly emerged adult fleas that wait for a host in carpets, rugs, upholstery, etc. This is not bad, because these fleas are precisely those more likely to jump onto the pet's owner. However, they will not catch fleas already on the pets, and will not eliminate the flea population.
  • Vacuuming as thorough as possible removes a lot of eggs, larvae, cocoons and adult fleas from carpets and rugs. It is especially recommended to do it shortly after treatment of facilities with insecticides because it stimulates the hatching of preemerged adults. Don't forget to eliminate the dust bag: larvae can continue development and cocoons can release adult fleas inside the bag!
  • Steam cleaning carpets, rugs and unpholstery also kills adult fleas and larvae.
  • Washing all cloth in pets' nests and craddles with detergents will also eliminate many immature fleas they may contain.
  • It has been proven that ultrasonic devices are ineffective for repelling fleas or for reducing flea infestations. They may even annoy pets because dogs and cats do hear certain ultrasounds that humans don't.

Flea vaccines for dogs and cats?

It has become quite usual among pet owners to talk about "flea vaccines". Most people mean those products that are administered to pets at monthly or longer intervals to keep them free of fleas. These products are mostly spot-ons (also called pipettes, drops-ons, squeeze-ons, etc.), pills or injections that provide such a protection. More about such products is explained further down in this article.

Strictly speaking, such products are not vaccines but classic chemical pesticides. Vaccines contain antigens of specific pathogen organisms (viruses, bacteria, etc.) that activate the immune system of the vaccinated animal or person to produce antibodies against the pathogen organism, i.e., vaccines stimulate the own defenses of the vaccinated organisms against pathogens. A few vaccines contain specific antibodies against specific pathogens, instead of antigens. What current flea products do is simply to kill or to sterilize fleas, but through simple chemical "poisoning", not through natural antibodies, neither produced by the pet's own immune system, nor administered with a vaccine.

Summarizing, there are no such true vaccines against fleas, neither for pets, nor for livestock or humans. A lot of research has been conducted on true flea vaccines, but so far without success. And it is unlikely that a real break-through may happen in the near future.

Natural flea repellents for dogs and cats?

There are no commercial repellents capable of keeping fleas away from pets, humans or animals for more than a few hours, if at all. Most natural or synthetic repellents target mosquitoes, and to some extent certain fly species, but are rather weak against fleas.

Several studies have shown that sulfur, beer yeast and B-complex vitamins have no repellent effect on pet fleas.

Biological control of fleas?

Biological control of fleas has been poorly investigated. In a few countries a product is available for the biological control of fleas outdoors using entomopathogenic roundworms. It can significantly reduce flea populations in lawns, gardens, etc. However, it is not effective against adult fleas on pets or indoors, which usually represent >95% of the flea problem. Learn more about biological control of insects.

Home-made traditional remedies against dog and cat fleas

There are many home-made remedies against fleas, most of them based on traditional recipes using locally available herbs or other natural products. They are the result of centuries of efforts for finding relief against fleas when modern insecticides were not available. 

The bottom line is that no such remedies are as effective as modern synthetic pesticides. They may bring partial relief for a few hours, maybe a few days, but certainly not week or month-long protection. They are often unreliable, and are completely insufficient to control flea populations established in a household.

It is good to know that in most countries such "natural products" (e.g. plant extracts) are submitted to less stringent regulations than veterinary parasiticides. This means that they don't need to proof their efficacy against parasites, or their safety for the pets, users and the environment through such strict and thorough investigations as the products containing synthetic parasiticides. Many regulatory authorities seem to simply assume that being natural they are "safe enough", or at least not harmful, and that users will find out themselves whether they are effective or not... Obviously, the cost and the know-how to develop and market such "natural products" is substantially lower than for veterinary medicines containing synthetic parasiticides. This low cost explains their proliferation. It is not possible to deal with such products here in detail. However, nothing speaks against trying them. If they work, fine. If they don't, you will never know whether the recipe is useless or whether you did something wrong. But it doesn't matter: just try another one.

BUT: when dealing with plant remedies, it is good to know that the active components in herbs are also chemicals, i.e. specific molecules that have a biological effect, in this case an insecticidal effect. They have been naturally synthesized inside the plants. But this says nothing about the safety of such chemicals. It is wrong and dangerous to believe that something is safe because it is natural! The most potent poisons known are often of plant or animal origin. And by the way, many such "natural products" that are used in numberless so-called "natural" or "bio" products are also industrially manufactured or synthesized.

Chemical control and prevention of dog and cat fleas 

A bit of recent flea control history...

In the last 25 years chemical control of fleas on pets has experienced a real revolution with dramatic improvements in efficacy and convenience (and prize...). Flea control on pets has become the largest Animal Health submarket. Several billion USD are sold every year. 

Until the late 1980's flea control products for on-animal use were not too effective and quite unreliable, but rather cheap. They were sold mainly over the counter (OTC) in pet shops, supermarkets and the like. They contained veteran insecticides such as organophosphatescarbamates and synthetic pyrethroids. Even earlier organochlorines were used as well. Since these products for on-animal use were not too effective, there was a strong need for complementary off-animal treatment of the household environment, which was accomplished by professional Pest Control Operators (PCOs) using the same veteran insecticides to treat carpets, furniture, lawns, etc.

Several multinational companies (Bayer, Merial, Novartis, Pfizer, etc.) discovered the huge latent potential and started a race to conquer this market. This race is still going! They did it with absolutely first priority over whatever other potential markets, especially over the livestock market. Hundreds of millions of USD have been invested in research, development and advertising on such new flea products. The result is an unprecedented arsenal of new products for flea control introduced in the last 25 years, whereas progress on livestock parasiticides has been miserable.

In addition, for strategic and regulatory reasons, almost all multinationals decided to market these new products as prescription-drugs through vets and pharmacies, whereas the old products were all sold prescription-free through OTC channels. By doing this, the new flea products became professional veterinary medicines and not simply better OTC flea pesticides. The bottom line is that this allowed much higher prices and margins, without price wars among competitors. It worked! Every pet owner knows that if it is true that many modern flea products are very effective, it is equally true that they are very expensive.

In the meantime, generics of those highly potent flea products have multiplied and prices are going down slowly. But the race continues, for the time being towards all-in-one flea products, i.e. control of adult fleas + flea larvae + ticks + mites + lice + roundworms + heartworms + tapeworms + ... with one spot-on, or one pill. We are not yet there, but quite close.

A collateral effect of this development was that sales of cheap and veteran OTC-products plunged, and the environmental flea control business of PCOs almost disappeared, because the new flea products for on-animal use are that effective, that environmental flea control is only seldom required.

Main flea control product categories

Nowadays there are two major product categories for on-animal flea control:

  • For external use:
    • Spot-ons = pipettes = drop-ons = squeeze-ons: dozens of brands, mostly for monthly administration
    • Collars impregnated with insecticides: dozens of brands, for long-term protection
    • The rest: shampoos, soaps, baths, sprays, aerosols, lotions, etc. hundreds of brands; the cheap alternative, very short protection
  • For internal use:
    • Tablets, pills, etc.  for oral administration: only a few brands, mostly for monthly administration
    • Liquids for oral administration: very few brands, mostly for monthly administration
    • Injectables: very few brands, for long-term protection

To learn more about general features of parasiticides click here
To learn more about general features of external parasiticides = ectoparasiticides click here
To learn more about delivery forms of parasiticides click here

Strategic requirements for successful flea control on dogs and cats

There are certain strategic conditions that ensure successful flea population control in a household when using products for monthly administration (spot-ons, tablets, etc.). If they are not followed, many fleas will be killed, but the problem won't be solved.

And keep in mind, that if you don't perceive a flea problem, it doesn't mean that there are no fleas. There may be a lot of preemerged adult fleas in the household waiting inside the cocoons for good hatching conditions.

All dogs and cats in a household must be treated

All dogs and cats can breed fleas. It happens sometimes, that in multi-pet households only one pet "shows" flea problems. This doesn't mean that the other pets don't have fleas, just that they are more tolerant. But all fleas reproduce and re-infest the environment with eggs. Therefore all pets have to be treated consequently.

If there are other small animals (e.g. guinea pigs, mice, rats, rabbits, etc.) in the same household, it is very likely that they have fleas as well and should be treated too. However, most dog and cat flea products are not approved for use on such other pets. In this case ask your veterinary doctor for advice.

Treatments must start at the onset of the flea season

The reason is simple. At the beginning of the flea season, the first generation of fleas hatch out of their cocoons and quickly find a host for blood feeding. These cocoons have overwintered in the environment. This first generation is usually not very numerous, maybe a dozen fleas. But uncontrolled, they will quickly produce thousands of eggs and hundreds of fleas in very few weeks. The few fleas of the first generation usually remain unnoticed by most pet owners. Therefore the first treatment should not wait until a flea problem is "perceived" but must be done as soon as possible: Around April in very cold regions (e.g. Canada, Scandinavia, etc.); already in March or February in less cold regions.

In many warm regions, seasonality is often driven by humidity rather than by temperature. Flea numbers will decline by dry weather and increase in the rainy season. The same rule applies: start the monthly treatments a few months before the problem usually "appears", i.e. before it is usually perceived.

In regions with constant hot and humid weather fleas are usually a year-round problem: it doesn't matter when to start. The key is to treat all pets in the household and to strictly keep the monthly intervals.

Treatment must continue during the whole flea season

In the cold regions of both hemispheres the flea season may last for 4 to 5 months, and the warmer it gets towards the tropics, the longer the season. It is crucial not to interrupt the treatments during the season, even if no fleas are "perceived" after a few treatments. As already explained, hatching of overwintering fleas out of their cocoons is staggered for weeks and even months. And pets can catch fleas outdoors. If such fleas are not killed, they will re-infest the household again. To ensure that they are killed, monthly treatments should not be interrupted.          

Spot-ons - pipettes, squeeze-ons, drop-ons - against fleas on dogs and cats

Spot-ons are ready-to-use concentrates containing one or more active ingredients with parasiticidal efficacy. Depending on the active ingredient(s) they are effective only against adult fleas, or also against immature stages, against various tick, mite or lice species, against internal parasites such as gastrointestinal worms, heartworm, tapeworms, etc. Most original spot-ons were introduced in the 1990s and 2000s and are responsible for most of the flea control "revolution" of the last 25 years. In the meantime generic spot-on brands have proliferated.

Spot-ons are for topical administration, i.e. on the skin of the pets. They are often sold in single-use squeezable vials or ampoules of different sizes for dogs or cats in a particular weight range. The whole content of a vial is applied on a given "spot" (typically on the neck or on the back). Once applied to the skin, the active ingredient spreads throughout the body of the pet or is absorbed through the skin into the pet's organism (so-called systemic products). Both spreading and/or absorption through the skin can be slower or faster, more or less complete, etc. depending on each animal's features (e.g. size, breed, hair coat, behavior, etc.) and also on the non-active, inert ingredients in the product, i.e. on its formulation, which can vary significantly between manufacturers. This is why product quality (and safety!) depends not only on the active ingredient(s), but also on the formulation (this is true for spot-ons and for whatever parasiticide or medicine, veterinary or human).

Most original spot-on brands claim to achieve a strong and fast curative (i.e. therapeutic) effect of established flea infestations, i.e. >90% (often >98%) within 1 to 3 days after a single treatment. Most of them also claim to provide a strong preventive (i.e. prophylactic) effect of about 4 weeks, whereby this preventive effect diminishes progressively from week 1 (often >99%) to week 4 (mostly <90%). As a general rule they deliver.

Most spot-ons are quite resistant to occasional washing and shampooing, i.e. the pet won't loose protection against fleas due to a splash. But repeated splashes or shampooing can indeed diminish the length or protection.

Most common original spot-on brands for flea control on dogs and cats

The best known original flea spot-on brands are the following:

  • FRONTLINE TOP SPOT, with fipronil, from MERIAL; available for dogs and cats worldwide. Introduced in the mid 1990s. Fipronil is a broad-spectrum contact insecticide and acaricide that kills the adult fleas (adulticide) and belongs to the phenylpyrazole pesticidesBesides fleas it also controls some pet ticks and lice. Fipronil is also vastly used in agriculture as well as in public and domestic hygiene. There are numerous generics.
  • ADVANTAGE, with imidacloprid, from BAYER. Available for dogs and cats worldwide. Introduced in the mid 1990s. Imidacloprid is a broad-spectrum contact insecticide that kills the adult fleas (adulticide) and belongs to the neonicotinoid pesticides. Besides fleas it also controls a few lice species, but not ticks. Imidacloprid is also vastly used in agriculture as well as in public and domestic hygiene. There are numerous generics.
    • Follow-up brands from BAYER:
      • ADVANTIX with imidacloprid and permethrin. Permethrin is a synthetic pyrethroid added to provide efficacy against ticks. Permethrin is also a broad-spectrum pesticide vastly used on livestock, in agriculture and in hygiene. ADVANTIX is available only for dogs, because permethrin is toxic for cats. 
      • K9 ADVANTIX with pyriproxyfen in addition to imidacloprid and permethrinPyriproxyfen is a juvenile hormone analogue, i.e. an insect development inhibitor, which prevents deposited eggs from hatching, because a few adult fleas may survive the imidacloprid treatment. It is available only for dogs in certain countries. Pyriproxyfen is also used in agriculture and hygiene.
      • ADVOCATE = ADVANTAGE MULTI, with imidacloprid and moxidectin. Moxidectin is a broad-spectrum macrocyclic lactone that adds efficacy against all major roundworms, including heartworms, asl well as against several mites and lice species, but is not effective against fleas. Moxidectin is also used on livestock but not in agriculture or hygiene.
  • PRAC-TIC, with pyriprole, from ELANCO (NOVARTIS). Available in the EU and other countries, but not yet everywhere, e.g. not in the USA. Only for dogs. Introduced in 2007. Pyriprole is a broad-spectrum contact insecticide and acaricide that kills the adult fleas (adulticide) and belongs to the phenylpyrazole pesticides. Besides fleas it also controls some pet ticks. Pyriprole is not used on livestock, agriculture or hygiene: it is only used on dogs. There are no generics so far.
  • REVOLUTION = STRONGHOLD, with selamectin, from ZOETIS (PFIZER). Available for dogs and cats worldwide. Introduced in the late 1990s. Selamectin is a macrocyclic lactone effective against adult fleas, certain lice, mite and tick species as well as against roundworms, including heartworms. It has a systemic mode of action, i.e., it is first absorbed through the skin into blood and then distributed through the whole body of the pet. There are no generics so far.
  • PROMERIS, with metaflumizone, from FORT DODGE (later PFIZER-ZOETIS). Available only for cats in certain countries. Metaflumizone is a broad-spectrum insecticide effective against adult fleas. It belongs to the semicarbazone pesticides. It was introduced by BASF for agricultural use in 2000. BASF does not market veterinary products. PROMERIS DUO, with metaflumizone and amitraz, also from FORT DODGE, only for dogs, because amitraz is toxic for cats. Amitraz adds efficacy against ticks. There are no generics so far.
    • NOTICE: In 2011 FORT DODGE announced the withdrawal of PROMERIS and PROMERIS DUO from the market for not fitting with their product range. The decission was perhaps related to reports that associated metaflumizone with a higher incidence of "pemphigus foliaceus" in pets, a type of autoimmune skin disorder. However, it is not clear whether this withdrawal has become effective worldwide. Some Fort Dodge websites (e.g. Brazil in January 2013) still include PROMERIS and PROMERIS DUO in their product range.
  • ASSURITY, with spinetoram, from ELANCO. Available only for cats in certain countries. It has been introduced in 2011. Spinetoram is a semi-synthetic broad-spectrum insecticide belonging to the chemical class of the spinosyns, closely related to spinosad. It is highly effective against fleas, but not against ticks. Spinetoram is also used in agriculture, but not on livestock. There are no generics so far.

Click here to learn more about spot-ons, pipettes, squeeze-ons: efficacy, safety, etc.

Insecticide-impregnated collars against fleas on dogs and cats

Before the introduction of modern spot-ons in the 1990s insecticide-impregnated collars were quite popular for pets against fleas and ticks. Many brands are still available.

Good collars should kill 80-90% of the fleas within 1 week after application and provide about 90 to 70% protection against re-infestation for 8 to 12 weeks, whereby efficacy usually diminishes during the last weeks.

Most collars consist of a plastic or a thick textile strip impregnated with an insecticide that is slowly released to the hair coat around the collar. It spreads more or less rapidly and completely to the rest of the hair coat. All insecticides used in collars kill adult fleas by contact.

Most insecticide-impregnated collars are quite resistant to occasional washing and shampooing, i.e. the pet won't loose protection against fleas due to a splash. But repeated splashes or shampooing can indeed diminish the length or protection.

Such collars contain mostly only one active ingredient, frequently a "veteran" from the following chemical classes:

A weakness of all these collars is that flea resistance to such veteran insecticides is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

All these pesticides are vastly used on livestock, as well as in agriculture and in public and domestic hygiene.

There are also collars impregnated with "soft" natural insecticides such as natural pyrethrins, d-limonene, linalool, etc.

Clik here to learn more about insecticide-impregnated collars: efficacy, safety, etc.

Shampoos, soaps, baths, sprays, against fleas on dogs and cats

A common feature to this category of flea control products is that protection against re-infestation is significantly shorter that spot-ons or collars. Depending on the product protection won't last longer than 2-4 days. This may be enough to clean a pet from fleas. But not to prevent newly emerged fleas to re-infest the pet. The reason is that most of these products are not resistant to water (shampooing, washing, rain, etc,.) and/or to exposure to sunlight. Such products are often cheaper than spot-ons or collars, but also less reliable.

In addition, whereas the curative efficacy of spot-ons and collars is usually >90%, it is significantly lower (70 to 85%) for these products. Administration is also less straightforward than for spot-ons and collars, which often leads to incorrect use that diminishes the efficacy.

These products are often not resistant against washing and shampooing, i.e., a simple splash may cause lost of whatever protection against fleas.

A further weakness of all these products is that flea resistance to such veteran insecticides is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

These products contain mostly "veteran" active ingredient from the following chemical classes, sometimes in mixtures.

Many such products contain also "soft" natural insecticides such as natural pyrethrins,, d-limonene, linalool, etc., often in mixtures with classic synthetic insecticides and with a synergist.

A further weakness of many of these products is that flea resistance to organophosphates, carbamates, synthetic pyrethroids and natural pyrethrins is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

Click here to learn more about shampoos, soaps, baths, sprays: efficacy, safety, etc.

Tablets pills, etc. for oral administration against dog and cat fleas

All products for internal use, including tablets, pills, etc. contain active ingredients with a systemic mode of action, i.e. once ingested they are absorbed into blood and distributed throughout the pet's body. They reach the fleas during their blood meals, wherever they are biting, which is not always the case for products for external use that act by contact. This means also that they remain unaffected by whatever external influences such as washing, shampooing, rain, exposure to sunlight, dirt, etc. 

Such products are a good option for pet owners that want to avoid getting themselves or their children in contact with pesticides, which is unavoidable when using topical products such as spot-ons, collars, shampoos, sprays, etc.

The best known original brands of flea pills and tablets are the following:

  • PROGRAM, with lufenuron, from ELANCO (NOVARTIS). Available worldwide only for dogs. Introduced around 1990. Program was the product the launched the "flea control revolution" previously mentioned. Lufenuron is a broad-spectrum insect development inhibitor belonging to the chemical class of the benzoylureas. Lufenuron does not kill the fleas on the pets, but makes that their eggs become sterile. For this reason it should be used as a preventative. If administered to heavily infested pets, since it does not kill them, it will take several weeks until they are free of fleas. Monthly administrations starting at the beginning of the flea season will effectively prevent the development of flea populations in the household. Lufenuron is also used in agriculture. There are a few generics.
  • CAPSTAR, with nitenpyram, from ELANCO (NOVARTIS). Available for dogs and cats worldwide. Introduced in the late 1990s. Nitenpyram is a broad-spectrum insecticide belonging to the neonicotinoid pesticides. Orally administered nitenpyram acts extremely quickly. It can kill all fleas on a pet within 2 to 4 hours after administration, whereas most other products need 24 to 48 hours. However, it has only 1-2 days residual effect, i.e. protection against re-infestation is very short. Nitenpyram is used in agriculture but not on livestock. So far there are no generics.
  • COMFORTIS, with spinosad, from ELANCO. Availabe only for dogs in certain countries. Introduced in the late 2000s. Spinosad is a broad-spectrum insecticide and acaricide of natural origin belonging to the spinosyns. Orally administered spinosad acts against fleas as fast as nitenpyram, i.e. it kills most of them within a few hours after administration. And it provides up to 4 weeks protection against re-infestation. Spinosad is used on livestock as well as in agriculture and hygiene. So far there are no generics.
  • BRAVECTO, with fluralaner, from MERCK (MSD) ANIMAL HEALTH. Availabe only for dogs in certain countries. Introduced in 2014. Fluralaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines. With a unique 3-month claim against ticks and fleas. There are no generics.
  • NEXGARD, with afoxolaner, from MERIAL. Availabe only for dogs in certain countries. Introduced in 2014. Afoxolaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines.
  • NEXGARD SPECTRA, with afoxolaner and milbemycin oxime, from MERIAL. Availabe only for dogs in certain countries. Introduced in 2015. For monthly administration against ticks, fleas, several roundworm species and for heartworm prevention.
  • SIMPARICA, with sarolaner, from ZOETIS. Availabe only for dogs in certain countries. Introduced in 2016. Sarolaner is one of the newest insecticidal active ingredients from the chemical class of the isoxazolines.

Click here to learn more about pills, tablets, etc: efficacy, safety, etc.

Liquid formulations for injection or oral delivery to dogs and cats against fleas

There are very few injectables or liquid oral formulations against fleas of pets. To my knowledge the only ones to be reasonably reliable are the following ones:

  • PROGRAM ORAL SUSPENSION with lufenuron, from ELANCO (NOVARTIS). For oral administration only to cats. Available in most countries. Introduced in the mid 1990s. Lufenuron is a broad-spectrum insect development inhibitor belonging to the chemical class of the benzoylureas. Lufenuron does not kill the fleas on the pets, but makes that their eggs become sterile. For this reason it should be used as a preventative. If administered to heavily infested pets, since it does not kill them, it will take several weeks until they are free of fleas. Monthly administrations starting at the beginning of the flea season will effectively prevent the development of flea populations in the household. Lufenuron is also used in agriculture.
  • PROGRAM 6 MONTHS INJECTABLE, with lufenuron, from ELANCO (NOVARTIS). Only for cats. Available in certain countries. Introduced in the late 1990s. A single injection is enough to cover the whole flea season in most regions with a cold winter.

Be aware that ivermectin products are always inadequate for controlling fleas! Unfortunately, with the proliferation of ivermectin brands, products of doubtful origin may appear that claim to control fleas on pets or livestock. They don't. The only macrocyclic lactone that controls fleas at the therapeutic dose is selamectin (active ingredient of STRONGHOLD = REVOLUTION). All other macrocyclic lactones do not control fleas.

Click here to learn more about injectables: efficacy, safety, etc.
Click here to learn more about drenches: efficacy, safety, etc.

Environmental control of dog and cat fleas 

On-animal control products may not be sufficient for controlling flea populations in a household and additional off-animal control measures may be required, e.g. treating carpets, rugs, furniture, uühpstery, lawns, etc. with adequate pesticides.

This was normally the case before the "flea control revolution" of the 1990s, because the products then available for on-animal treatment were not potent enough. Nowadays, most modern flea control products for monthly administration are strong enough to make off-animal environmental treatments superfluous. However, such modern products are expensive and not affordable for everybody. If such products cannot be regularly used, environmental control may be unavoidable in order to really control flea populations.

In most countries only certified Pest Control Operators (PCOs) are allowed to perform environmental flea control with pesticides. The reason is that the use of the required pesticides is restricted to professionals for safety reasons. In fact, large-scale use of pesticides indoors in households or other premises is not trivial and bears significant safety risks if done improperly.

Most products for environmental flea control used by PCOs contain classic synthetic pesticides of the following chemical classes:

Most of these products are available only for PCOs in the form of concentrates. They have to be correctly diluted before usage, and application requires specific equipment and appropriate training. Some of these concentrates are notably more toxic than the ready-to-use products available for on-animal control. Many of these products are the same that are used against cockroaches, termites, and other household pests.

If you ask a PCO for flea control in your household, the key for successful environmental flea control is to adequately treat those places were immature flea stages (eggs, larvae, cocoons) tend to concentrate, i.e. those places the pets prefer for sleeping and resting.

  • Indoors: typical places to treat are sleeping places (cradles, nests, etc.), dark corners below furniture, in bathrooms, basements, cellars, etc. Carpets, rugs, mattresses, cushions, textile upholstery, etc. are also ideal flea breeding places. Dry pet or livestock bedding and dry sandy soils are also excellentflea breeding environments. Hard and plastic flooring (stone, tiles, wooden parquet, etc.) are much less appropriate for flea breading. However, gaps or cracks (e.g. between parquet slates) filled with dirt can also support flea development.
  • Outdoors. Key places to treat are in and around doghouses, hiding places below the house, in dark corners under tress or brushes. Vehicles used for pet transport should also be treated.

After a first treatment, the level of flea infestation has to be monitored to estimate the need for further treatments. This can be done regularly combing your pet for fleas and recording the numbers caught.  It can also be done with sticky rolls that you can roll over carpets or furniture you believe most infested with fleas. Another monitoring method is to walk around the house with long white socks and count the fleas that jump onto the socks.

A weakness of many of these products is that flea resistance to organophosphates, carbamatessynthetic pyrethroids and natural pyrethrins is quite frequent worldwide, which can significantly reduce their efficacy and length of protection.

Flea resistance to insecticides

Resistance of the cat flea (Ctenocephalides felis) and other flea species to veteran insecticides (carbamates, organophosphates, organochlorines, synthetic pyrethroids, etc.) is widespread worldwide. Resistance to synthetic pyrethroids may be that high, that it not only reduces the efficacy or the length of protection, but it makes the product completely useless. Resistance to organophosphates and carbamates it usually less strong and affected products will provide some level of control.

This means that if a product containing such pesticides does not meet the expectations raised in the label, it can be due to resistance. This may be the case for numerous, shampoos, soaps, sprays, aerosols, baths, insecticide-impregnated collars, etc. But don't forget that most product failures are due to incorrect use.

So far there are no reports on confirmed field resistance of fleas to newer insecticides such as those used in most flea spot-ons or tablets (e.g. lufenuron, metaflumizone, nenonicotinoids, phenylpyrazoles, selamectin, spinosyns, etc.). But nobody knows what will happen. The massive use of flea insecticides in many countries puts the flea populations under a tremendous selective pressure. The experience shows that this is the best way to select for resistance fleas. So the question seems to be not whether resistance to the newer insecticides will appear, but rather when and where it will be appear.

To diminish the risk that it appears precisely in your household, it is highly advisable to regularly change the flea control products you are using (e.g. every 2 or 3 years) making sure that the new product has a different mode of action, i.e. it belongs to a different chemical class than the previous one. If you have used a product with a phenylpyrazole (e.g. fipronil or pyriprole) for several years, consider changing to a product with a neonicotinoid (e.g. imidacloprid, dinotefuran), a spinosyn (e.g. spinosad or spinetoram), a benzoylurea (e.g. lufenuron), a macrocyclic lactone (e.g. selamectin), an oxadiazine (indoxacarb) or an isoxazoline (afoxolaner, fluralaner); or vice-versa. This periodic alternation of active ingredients with different modes of action to delay resistance is called rotation. An reasonable alternative to rotation is using a product that contains a mixture of two active ingredients with different modes of action (e.g. a flea killer combined with an insect development inhibitor).

If a product fails to meet the expectations, it is almost impossible for a pet owner to find out whether it is due to resistance, to incorrect use of the right product, or to correct use of the wrong product. Since there are so many alternative brands with many active ingredients and mixtures, the best solution is often to simply try another product with an active ingredient of a different chemical class. If a second product of a different chemical class also fails, chances are high that failure is due to incorrect use.

Learn more about parasite resistance and how it develops.

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