Life Cycle
The most prevalent species of flea to infest pets in Canada is the cat flea. For this reason, discussion of the life cycle will center on this species. The cat flea life cycle has four stages:

Click here for a picture of the flea life cycle.

Egg Stage
Once on a host, adult cat fleas take a blood meal and mate. Within 36 to 48 hours, the female begins laying eggs. Flea eggs are pearly white, oval with rounded ends and approximately 0.5 mm long. Eggs typically make up 50% of an infestation in the home. The female flea lays her eggs in the haircoat of the host. Since the eggs are not sticky, they readily fall off the host into the environment. Thus, flea eggs are deposited in only those places where the host has access. Female fleas can lay from 20 to 50 eggs a day and up to 2000 eggs during their lifetimes. Eggs usually hatch in 1 to 10 days, depending on temperature and humidity. Humidities below 50% and over 92% kill flea eggs.

Larval Stage
Newly hatched flea larvae are slender, white, segmented and worm-like. They are sparsely covered with short hairs and are 1 to 2 mm in length. They have an egg-tooth, similar to that of a bird, that they use to cut their way out of the egg. Larvae are free moving, and survive by feeding on organic debris found in their environment and on adult flea feces, which is essential for successful development. Once the larvae have ingested adult flea feces or other material they become darker in color. They have been observed to crawl as far as 20 feet while in this stage of their life cycle.

Since larvae are negatively phototactic (avoid light) and positively geotropic (prefer to move downward), they are found deep in carpet fibers, mattress or couch stuffing materials or organic debris (branches, leaves, etc.). They accumulate in areas where the animal spends a great amount of time. These "hotspots" are typically in pet resting areas. They are not usually found in open lawn. Flea larvae are extremely susceptible to heat and desiccation. Moisture in the larval environment is essential for development; relative humidities below 50% cause desiccation. Flea larvae undergo two molts before developing into the Pupael stage. While the first larval instar is no more than 2 mm long, the fully developed larvae can be 4 to 5 mm in length. The larval stage usually lasts 5 to 11 days, depending upon the availability of food and the climatic conditions, and will account for about 35% of an infestation in a home.

The transition from egg to larva, between molts and from larva to pupa, is controlled by juvenile hormone. When the juvenile hormone level drops, the larva molts to the next stage. The actual molting process is triggered by another hormone, ecdyson.

Pupael Stage
Upon completion of development, the mature larva produces a silk-like cocoon in which it pupates. The cocoon is ovoid, whitish, and loosely spun. Because the cocoon is sticky, it quickly becomes coated with debris from the environment which helps camouflage it. In most homes, the pupation can be completed within 5 to 14 days in ideal conditions. Once the pupa has fully developed, the adult flea (pre-emerged adult) will remain inside the cocoon for several days to several weeks until stimulated to emerge form the cocoon. Physical pressure (being stepped on), carbon dioxide (that mammals exhale), vibration (from walking, or vacuuming) and heat (generated by potential hosts or heated homes) can all stimulate emergence. It is interesting to note that flea pupae do not hatch all at once regardless of the stimuli. It is believed there is some type of communication involved (Pheromonal?, Genetic?) that causes flea pupae to stagger there hatching over a varied period of time. This effect is sometimes mistakenly perceived as a flea control product failure when it is in fact a normal mechanism of the flea to increase the likelihood of survival.

The fully formed adult flea residing in the cocoon (pre-emerged adult) is the stage that can extend the longevity of the flea, and makes it the most troublesome from a control standpoint. If the pre-emerged adult does not receive the proper stimulus to emerge, it can remain dormant in the cocoon for several weeks and possibly as long as one year in rare conditions, until a suitable host arrives. Added to this is the fact that there are no chemical sprays available on the market today that can penetrate the pupael cocoon. House sprays will kill exposed eggs and larvae, but pupae will remain unaffected and will hatch at some point long after the residual effect of most sprays has expired. Successful treatment of pupae must usually wait until it has hatched into an adult where it may then be killed with an adulticide. Cocoon's are typically spun around the base of carpet fibers or bedding material which make them impossible to remove with regular vacuuming. Vacuuming is recommended though as the vibration from the vacuum may stimulate the flea to the point of emergence where it can then be killed.

Pupae commonly make up 10% of the infestation in a home. Depending upon temperature and humidity, the entire life cycle of the cat flea can be completed in as little as 12 to 14 days under ideal conditions, or be prolonged to 6 months and possibly as long as a year in rare instances. However, under most average household conditions, cat fleas will complete their life cycle within 3 to 4 weeks.

Pupael Window Effect
Once adult fleas begin to emerge from cocoons, they are vulnerable to insecticides. However, after treatment with an adulticide pupae will continue to emerge for at least 2 to 4 weeks. In fact, small numbers of fleas may continue to emerge for periods up to one year; a phenomenon called "delayed emergence." Or "Delayed Pupael Hatching" This continued emergence of fleas following treatment is called the Pupael Window.

The pitfalls of the Pupael Window Effect are:
1. Re-treatment with adulticides on the pet is needed to control the emerging fleas; and
2. Pet owners unaware of the effect may believe the control measures used aren't working and either discontinue them or switch to other, perhaps less effective methods.

A common story owners relate, is they visit a cottage for the first time since last season. Within minutes of entering they notice that their pet is covered in fleas or that their legs are being bitten by small fleas. These smaller fleas are newly emerged adults that have remained dormant since the last visit and the presence of the family has stimulated the emergence.

Adult Stage
Once the flea emerges form the cocoon, it immediately begins seeking a host. A flea that emerges from the pupael cocoon due to the pressure of the pet stepping on it, can hatch, jump on the pet as it is walking by, and begin feeding in as little as 7 seconds. There is nothing currently available that is able to prevent the flea from jumping on the pet and feeding due to the short time frame involved. There are no repellents for fleas. Contrary to some myths, fleas are not repelled or killed by such items as garlic or brewers yeast. In laboratory experiments fleas were fed brewers yeast in order to sustain them until a blood meal could be introduced. There is also no clinical data to support theory of sonic flea control devices. Owners that experience success with these types of treatments are usually the lucky few that would not suffer from fleas regardless of what the pet is on. Newly emerged fleas are attracted to pets by various stimuli produced by these hosts: body heat, movement and exhaled carbon dioxide. In contrast to larvae, adult cat fleas will orient and move towards light. The adult is negatively geotactic (prefers to move upward). These behaviors enhance the cat flea's success in finding a host because newly emerged fleas move directly to the top of the carpet pile where they are more likely to encounter a passing host. The presence of fleas is not an indication of a "dirty" home. Regardless of sanitary conditions a flea is able to survive in a home as long as there is a host on which to feed.

If the newly emerged cat flea does not find a host, it can survive for 1 to 3 weeks before requiring a blood meal, but once they initiate feeding the flea must be able to feed again within 4 days or it will die.

Adult fleas are dark reddish-brown and 2 to 5 mm long. They have thin, flattened bodies and backward-directing spines on their legs and bodies that facilitate forward movement through fur, hair or feathers and prevent them from being easily dislodged.

Click here to see a picture of a flea on the head of a pin.

Adults make up only about 5% of a population. Fleas are wingless, but have strongly developed legs that permit them to jump up to 100 times their own body length (8 inches vertically and 15 inches horizontally). That's the equivalent of a human jumping the length of three football fields. The g forces (gravity pull) on the flea measure about 150g's as it jumps. Compare that to the g force of 3 that astronauts experience as the space shuttle takes off. Fleas are very resilient in their environment due to their strong insect exoskeletons made up of a substance called chitin (KITE-IN). It is this shell that helps the flea survive on the pet. Once on a host, the cat flea initiates feeding within seconds and egg production begins within 48 hours. Contrary to what has been commonly reported, the adult cat flea is actually a permanent ectoparasite. It does not leave the host unless it is forced off.

Therefore, once on a suitable host, fleas do not leave their host voluntarily. They remain until removed by ingestion, grooming behavior, die a natural death, or die from chemical induced death (insecticide application). The drawback with any adulticide only treatment is the 85% of the pre-adults waiting to develop in the environment. The adult cat flea can survive on the host and maintain some reproduction for 2-4 weeks under most natural conditions, but if not killed prematurely an adult flea may live as long as 4 months.

Feeding Habits
Fleas feed through a proboscis, or long, slender mouth part. The tip, which is only 1/10 the size of a skin cell, is tapered like a needle for easy penetration. Once the proboscis is inserted, the flea moves around until it finds a blood vessel and begins to suck. Before feeding, it pumps saliva into the wound through two small channels on its mouth part to prevent the blood from clotting. It is the injection of this saliva that is responsible for the irritation that some pets experience when they suffer from a flea allergy dermatitis. Sometimes a single flea bite is enough to incite a reaction in a pet sensitized to the bites.

In order to produce an egg mass equal to 1 to 2 times their body weight daily, female cat fleas must consume large quantities of blood. Female fleas reach their maximum size 48 hours after initiating feeding, up to a 140% increase. Males, however, only increase in size approximately 20% over their emergence weight. During active reproduction, female cat fleas can consume up to 13 ul of blood per day, which is equivalent to 15 times their body weight. 72 female fleas are capable of sucking 1 ml of blood per day.

During feeding, female cat fleas excrete large quantities of incompletely digested blood which dries within minutes into reddish-black fecal pellets or "flea dirt." Flea feces may appear as long tubular coils or as fine pellets, depending upon the duration of uninterrupted feeding. Coils are produced only if female fleas are allowed to feed uninterrupted for a few hours. The dried fecal material falls off the host into the environment where it serves as essential food for the larvae. Flea feces can often be found matted into the haircoat and is diagnostic for the current or recent presence of fleas.

Preferred Climate
Fleas thrive in moist, warm climates, which explains their prevalence in coastal and warm and humid areas during the spring and summer. In homes where fleas went untreated during the peak months of the year, fleas are able to continue through their life cycle to the point of the pupael stage. Here they will remain dormant until the humidity rises. Come spring, the untreated home will be inundated by a new generation of fleas.

Cat fleas are apparently intolerant of cold. No life cycle stage (egg, larva, pupa or adult) can survive for 10 days at 3°C (37.4°F) or 5 days at 1°C (33.8°F). Therefore, cat fleas associated with dogs in cold climates are most likely surviving as adults on untreated dogs and cats or small wild mammals such as raccoons and opossums in the urban environment. As these animals pass through yards in the spring or set up nesting sites in crawl spaces or attics, the eggs laid by surviving female fleas drop off and subsequently develop to adults. Cat fleas may also survive the winter as pre-emerged adults in environments sheltered from the cold. A flea's environment is critical to its development. In the house, they are likely to be found as immature stages in bedding, carpets, basements, sofas, beds etc.

Outdoors they are found wherever the pet might rest during the heat of the day, including such areas as dog houses, flower beds, under bushes, crawl spaces, under decks etc. Outdoor instances of re-infestations are usually minimal compared to internal ones. Outdoor fleas account for about 1% of the total population.

Flea-Related Problems in Dogs
Biting or scratching is usually the first sign of reaction in an animal with fleas. Some animals may begin excessive grooming to try to rid themselves of the irritation, eating many of the fleas in the process. Light-haired dogs who do this may develop an orange-brown discoloration due to salivary staining. These general symptoms are usually referred to as pruritus.

Pruritus
Pruritus (itching) is caused by reactions to flea saliva. During feeding, the flea releases saliva to stop blood from coagulating. The saliva contains chemicals that cause an irritant reaction in the host:

Some animals have a higher tolerance to fleas and aren't disturbed by them. Others suffer varying levels of irritation and may show a reaction after only one bite.

Flea Allergy Dermatitis (FAD)
Dogs that are hypersensitive to flea saliva have intense reactions, often out of proportion to the number of pests on the dog. Recent research indicates that FAD may be caused by intermittent exposure to large numbers of fleas. Animals sensitized in this way may subsequently become intensely reactive even when only a small number of fleas are present. This is significant as it suggests the way to prevent FAD may be to prevent the repeated exposure to flea infestation.

The initial reaction is usually a reddened wheal, which forms a papule or swollen nodule and crusts over. After that, several secondary changes are possible:

The pruritus, or itching, that occurs in dogs with FAD is intense, and results in self-mutilation. Generally, clinical signs are distributed over the inner thigh and abdomen and along the spine and hindquarters. Corticosteroids are often used to temporarily relieve clinical signs, and this recommendation must come from your veterinarian, but a flea control program is needed to resolve the problem completely.

Tapeworm (Dipylidium caninum)
This particular species of tapeworm must use the flea as an intermediate host in its own life cycle. Egg packets deposited by the adult tapeworm are shed into the environment where they are consumed by the flea larvae. If a pet ingests an adult flea that consumed the tapeworm egg pack as a larvae, the tapeworm parasite is passed on. Although tapeworm in pets usually doesn't cause serious disease, it is particularly annoying to pet owners. Tapeworms are easily detected by the pet owner. Small rice-like objects are seen clinging to the hind end of the animal near the base of the tail, and their presence usually evokes a feeling of disgust in most owners. In addition, people can become infested if they inadvertently ingest infected fleas.

Anemia
Being blood-sucking insects, fleas can produce parasitic anemia in heavy infestations, particularly in young animals. Fleas in the genus Ctenocephalides have been reported to produce anemia in dogs, cats, goats, cattle and sheep. Severe flea infestations in young pups can cause anemia to the point of death.

Flea-Related Conditions in Humans
Fleas are able to reproduce on any mammalian blood supply, including humans. However, a female flea must feed for a prolonged period of time in order to begin egg production. Fleas may spend 2-3 hours sucking on one spot and most humans will scratch or perform some other action to interrupt this feeding process. As such, the flea is not able to feed for the required length of time to produce eggs.

Disease transmission due to fleas in man is not a common occurrence, but any suspected reactions should be discussed with a human doctor.

Diagnostic Options
Flea infestations are initially diagnosed based on clinical signs and observation of fleas or flea dirt (dried flea feces) by the owner or the veterinarian. Procedures may include:

Flea Control
Literally thousands of products over the years have been used in the battle for flea control. However, most share a common drawback. They are directed toward only 5% of the flea population - the adults . The other 95% of the population consists of eggs, larvae, and pupae that hide in carpets, pet bedding, dog houses, etc., are unaffected by most flea control products.

There are several disadvantages to this " Adults only " approach to flea control: