By Dr. Richard and Patricia Kaae.

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.  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. 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.


Flea Scanning Electron Micrograph False Color.jpgFile:Pulex irritans female ZSM.jpg


Left. Electron Microscopic  Image of Adult Flea. Public Domain. Right. Normal Flea Coloration. Image Courtesy CatjaZSM-CC BY-SA 3.0.


Fleas have a limited sense of smell with very small antennae that are concealed on the side of the head grooves.  However, they can detect carbon dioxide, thus possibly explaining why fleas get excited and jump wildly when coming in contact with a person's or some other host’s breath.  Depending on the species, fleas may or may not possess eyes; but even in the case of the former, they are thought to have a limited sense of vision and can only detect changing patterns of light and shadows.  Their bodies have a variety of sensory organs (hairs and spines) that can detect the vibrations in a variety of their hosts.  In summary, fleas are well adapted for detecting a host using smell (CO2), vibrations and shadows.  This ability was documented by a study conducted on rabbit fleas.  A large number (over 250) of adult fleas were marked and released in an 18,000 square foot enclosed area.  Subsequently, three rabbits were released in the field. Approximately half of the released fleas were removed from the rabbits after several days.


Flea Biology. Fleas are typically found on birds and mammals with over 1,600 species occurring worldwide.  Based on feeding habits, there are three main types.  The first type does not attach to the host while feeding.  And as a result, these fleas readily move from one host to another as is the case with most species that belong in this category.  The second group includes females that readily attach by their mouthparts to their host while feeding.  The final group includes gravid females that develop under the skin of the host and keep a breathing pore to the outside. 

The life biology of most common fleas found in the United States is quite similar.  The following is based on the most common fleas occurring on pets, namely the cat and dog fleas, Ctenocephalides felis and Ctenocephalides canis. As with most fleas in temperate areas, infestations tend to be seasonal with peak populations in the summer months. In the colder regions, they decrease to very low or sometimes almost non-existent populations 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 when the pet owner lives in warmer tropical areas, flea season can be year around.


The flea spends almost all of its adult stage on the host.  As with most fleas, the cat flea and dog fleas have 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 modified for slicing the skin and subsequently siphoning blood.  In order to produce eggs, the female requires a daily blood feeding. Once fed the female typically deposits her eggs on the host; however, most subsequently drop off the host as they are relatively dry.  The eggs are relatively large for such small insects, about the size of a grain of salt or approximately 1/2 the size of the adult flea.  They are white, oval and rounded at each end.  A female flea deposits several eggs a day (if fed daily), but because they are long lived (months) she is capable of producing 300 to 400 eggs during her lifetime.  When an infested pet (such as a cat during flea season) sleeps on a table or other surface and then leaves, it almost appears as though someone has taken salt and pepper and sprinkled it on this surface.  This is called the “salt and pepper effect.”  The “salt” is the fleas’ eggs and the “pepper” is the feces of the adult flea.


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 larvae are elongated, lack legs and possess a well-developed head capsule and elongated hairs on the body.  When disturbed, these larvae will characteristically flip in circles.  The larval stage is a scavenger feeding on any of a variety organic matter, including feces, dander, food particles and other organic matter.  One of the main ingredients in their diet is the adult feces, which is quite high in protein It contains a considerable amount of dried blood.  Adult fleas bite and feed many more times than needed in order to fulfill their nutritional requirements.  As a result, their feces is very high in partially or undigested blood.  This is a rather 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. 


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Larval Stage of a Flea, a Scavenger.  Image Courtesy of Kalumet-CC BY-SA 3.0


Development of the larval stage may be completed in as little as nine days or, under unfavorable conditions (low temperatures), can be extended as long as 200 days.  Larval development is normally restricted to protected places where there is at least 75% relative humidity. Once the larva completes its development, it spins a loose cocoon around its body and pupates.  The pupae (Figure 10) usually are covered by bits of their environment, including such materials as hair, dirt, lint and sand.  Again, the developmental length of the pupal stage is quite variable, but at room temperature approaches two weeks.


The Pupa in Case (left). Pupa (right) Removed from Case.  Image Courtesy of Department of Parasitology, University of Sao Paulo, Brazil.


Once the adult flea emerges from the pupa it remains in the silken cocoons until the presence of an approaching host (cat, dog, human) trigger them out. Prior to emergence from the cocoon an adult can survive for an extended period of time (over 350 days or more).  However, once emerged, the adult flea requires a blood meal or it will die in a few days.  Under ideal conditions some species can live for more than a year. The longest recorded life cycle of a flea is 996 days for 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 Sheppard 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 (just kidding Sally and Mini-my dogs, almost forgot the cats Einstein, Pissy, Food, Wallet and Buster).


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 people, 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 because it has been vacant for two 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 had 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. The main rat during the historical world major plagues was the so called black rats (Rattus rattus) which today this is better known as the roof rat.   Today the dominant rat in many areas of the world is the Norway rat (Rattus norvegicus) although the roof rat is quite common in many areas of the United States. The roof rat is more conducive (somewhat domesticated) to living indoors and is a better climber than the heavier bodied Norway rat.  In addition the roof rat rarely moves more than 200 meters from their nest, hence their adaptability to the thatched roof homes or other historical type structures. . When the plague bacterium causes the disease in rodents it is referred to as sylvatic plague.  When rats initially infected they are asymptomatic until near death. As the infection reaches maturity, the rats swell up because the bacteria (Yersinia pestis) increase so rapidly and in such large numbers). At this point the rats stagger as if intoxicated. Once the host dies (rats) the fleas leave their dying hosts and seek the nearest warm-blooded animals. In the case of the major plagues of the world this was frequently a human.


There are 3 forms of plague, namely bubonic, septicemia, and pneumonic. All are caused by the same bacterium, Yersinia pestis. Each form of this disease kills victims in different ways. With bubonic plague one to six days after a human is bitten by an infected flea, the lymph nodes (in the armpit, groin) become tender and swell in size from that of an egg to a tennis ball. These very swollen lymph nodes areas are called buboes. As buboes increase in size they may break and discharge pus.


On occasion the bite site becomes infected and turns gangrenous and necrotic. Other symptoms include headaches, nausea, vomiting, aching joints, high fever of 101-105 degrees, and a general feeling of illness. Symptoms can take from 1-7 days to appear. Subsequently if the fever breaks, remission can occur and the victims’ immune system kicks in thus eliminating the bacterium and symptoms. If the fever doesn't break, the infection will spreads to the blood, causing septicemia will almost always results in death. Although some victims survive, (at that time (historical) the mortality rate was 30-75%) the manifestation of these lesions usually indicated the victim had a life expectancy of up to a week.


In some instances the infection can proceed directly to the blood stream resulting septicemic Plague and can occur before the formation of buboes (frequently and diagnostic symptom) and results in death before a diagnosis can be made. Reportedly septicemic plague can even be carried by either the human flea or the body louse. With septicemic plague, blood vessels break and leak under the skin causing a dark rash (consequently the historic name of the 1500s-Black Death). For both bubonic and septicemic Plague, there is bleeding), multiple system failure, and death. All of this occurs within 3 to 7 days. The mortality rate for septicemic plague is 100 percent. Once established in a human population this disease can change to a more contagious if not more virulent form. This occurs once the infection reaches the lungs. Once there the victims initially cough up a blood-spotted mucus which is followed by a bloody froth and bacteria laden air born droplets.  Of course these tiny droplets are extremely contagious and are spread much like the flue or a common cold.  As with septicemic plague, pneumonic plague has a 100% mortality rate (if untreated0 and death can occur in a matter of hours.


Some modern antibiotics are available for treatment for the three types of plague. Streptomycin, tetracycline and gentamicin are all effective with maximum effect if given within the first 18 hours of the initiation of symptoms. Penicillin on the other hand is not effective.


Major Plagues of the World. The use of Quarantine was quite common with many plagues.  A common situation was when a ship entered a harbor and was suspected of carrying plague, quarantine was imposed on the vessel. In the fourteenth century, many cities strictly employed quarantines by sealing off homes and allowing the sick and probably anyone else in the home left to die.


From 1150-1200 there was a major climate warming in much of Europe. This along with the rise of a mercantile class, led to improved diet and greater population growth. As a result, by 1340, Europe in general was significantly overpopulated. This came about during a significant cold spell (the so-called Little Ice Age) which ended by 1351. During this climate change it was colder and wetter than normal. With the previous increase in population and resultant crop yields reduction, individual caloric intake fell and, general health declined.  Unfortunately, the pest population increased. With crowded conditions, a reduction in general health and the abundance of disease vectors, the development of a higher number of diseases was predictable (probably not at that time of course).


It’s amazing that human civilization survived the Plague. Ignorance and superstition, on top of unsanitary conditions, food shortages, and crime, were the worst-case scenarios that existed at the time.  People often died in such numbers that proper disposal of their corpses was impossible and they were left in large mounds to be fed on by dogs and rats. Unsanitary conditions accelerated the spread of the plague. Yelling, “Look out” from upper story windows, people emptied their chamber pots into the narrow streets, along with the mud and garbage, creating unsanitary conditions and making travel difficult. The typical home wasn’t much healthier than the streets, consisting of dirt floors, straw roofs and walls made of a dirt/straw combination. Animals were kept inside with the family. Lack of warm water and a moral response to scandalous Roman bath houses meant that people rarely bathed and were infested with plague-carrying fleas. Observers at the time recorded that during the burial preparation of a well-known religious figure so many fleas emerged from his clothing that his corpse “boiled over with them like water in a simmering cauldron.”

Popular children’s rhymes, like “Ring around the Rosie’s,” reflected the terror caused by the Plague. In the lyrics, “Ring around the rosies, pockets full of posies, ashes, ashes, all fall down,”; rosies referred to rosary beads that were meant to protect the wearer from this mysterious enemy. Flowers (posies) were carried to mask the foul odor attached to plague victims. Ashes refer to the remnants of the burnt corpses. “All fall down” refers the masses of dying plague victims. An alternative last verse was “A tishoo, a tishoo,” referred to a common symptom of pneumonic plague, the sneeze, a death sentence to nearly anyone it landed on.

The plague brought civilization throughout Europe to a standstill. Bureaucrats died en masse, governments fell along with civil authority, and crime became rampant. Farmers fled from their fields or died in them, creating food shortages. Many areas were abandoned. Plague attacked merchants and peasants alike. Only the very rich could afford to move far from the disease, and even that was no guarantee of immunity.

Unaware of the plague’s causes, people dipped handkerchiefs in aromatic oils, bathed in human urine, fired cannons wearing talismans, bled themselves with leeches, placed dead animals in their dwellings, did bloodletting, drank the pus extracted from a suppurated bubo (gross), applied dried toads in order to relieve the pain of the buboes by absorbing the "poisons,” and (only for the very rich, of course) drank liquid gold or powdered emeralds.

Upon commission of the pope in 1348, a group of “learned” medical men of in Paris concluded that the disaster was a result of a conjunction of Saturn, Jupiter, and Mars in the 40th degree of Aquarius at 1:00 p.m. on March 20, 1345. This caused hot, moist conditions, which forced the earth to exhale a virulent sulfurous miasma, they said.

So much for the Age of Aquarius!

The horror and fear faced by medieval people confronted with previously unknown symptoms of this disease is inconceivable to us today. To those who believed in spirits and devils (most people at the time), the Plague was their worst nightmare, one from which there was no relief or cure. It was as if all the monsters of their psyches were unleashed for incomprehensible reasons. When your worldview is limited, your options in the face of calamity seem even more limited. Any explanation is believable, including divine punishment, which local clergy blamed for the Plague.

The Plague, like most incomprehensible human tragedies, ripped off the thin veneer of human rationality and created a horrific search for scapegoats. Xenophobia was the norm—all strangers were suspected of spreading disease. Jews were the targets of choice (even though they died of plague at the same rate as others), however. Rumors that they poisoned wells ran rampant. There were pogroms and massacres. The rabble was loose.

Zurich expelled all its Jews and closed its gates to them. Two-thousand Jews were burned to death by a mob in Stausborg on a single day in 1349. Even officialdom entered the fray. The canton of Basel gathered all 4,500 of its Jews in a specially built structure on an island in the Rhine and burned them to death, after which the town fathers passed a law forbidding Jewish residence in the canton for 200 years. Six-thousand Jews were incinerated in Mainz, Germany, after they fought and killed 200 members of an attacking mob.

Pogroms also occurred in Baden, Brussels, Burren, Dresden, Eisenach, Erfurt, Freiburg, Gotha, Landsberg, Lindau, Memmingen, Solothurn, Speyer, Stuttgart, Ulm, Worms, and Zofingen. There were over 350 separate recorded massacres of Jews during the years of the Plague.

When the Plague ebbed at the end of 1351, it left Europe with a sizable shortage of workers, which helped to destroy the feudal system by creating a seller’s market for labor. Wealth was redistributed as the poor and homeless took over abandoned homes.

As mentioned earlier, the Plague’s most generally agreed upon mortality figures are 20 million in Europe and perhaps 40 million worldwide. It seems impossible to imagine the sheer terror a person might feel as family and friends dropped dead all around. They were healthy in the morning and dead by evening in many cases.

The last major infestation of plague arose in China and India in 1855 and reached Hong Kong in 1894. Estimates are that 12 million died. Today, plague is endemic in various places. Madagascar, Tanzania, Brazil, Peru, Burma, and Vietnam have experienced cases almost every year since the start of the last pandemic in 1880, and rodents in the southwestern United States carry it. In fact, 40 percent of the U.S land area is infested by plague-infected animals, mostly prairie dogs. Some national parks have signs saying not to feed the squirrels because they have plague.

Today, east Africa and Hunan province in China are permanent reservoirs, called inveterate foci, for the disease. From 1965-1971, Vietnam (in addition to fighting a war against the United States) reported 25,000 cases of Plague. The World Health Organization received reports of 18,739 cases in the period from 1980-1994, of which there were 1853 deaths (a 10 percent death rate) and between 2000 and 3000 every year. What is disconcerting being that more cases were reported from 1990-1994 than in the entire previous decade (an average of 2025 cases/year versus 861 cases/year).


The latest large, but not major, outbreak occurred on September 20, 1994 in the Indian city of Surat in the state of Gujarat. Initially the government of India did not recognize the presence of the disease until several hundred thousand people had fled the region. By October 2, there had been 2500 cases reported and official figures of 58 deaths. Considering that this strain was the highly contagious pneumonic variety, thus spread by aerosol droplets upon respiration and was amenable to treatment with tetracycline, such a low mortality figure may or may not be comforting.


A vaccine was available for those who expected to come in contact with animals that may have been infected, but it was not completely effective. The manufacturer discontinued production in 1999 and it is no longer available. It worked on bubonic Plague but not pneumonic.

Rather ominously, the September 4, 1997 issue of the New England Journal of Medicine carried a brief report from Galimand et al. describing a case of multiple antibiotic resistant bubonic Plague. The causative agent, Y. pestis, acquired a resistance plasmid from an unknown source. The thought of another worldwide pandemic of Plague that is resistant to modern medical treatment boggles the mind.


On August 26, 1999 the wire services carried a story announcing the development of a vaccine for bubonic Plague designed to protect against bio-terrorism. Human trials were to begin shortly. We await the results. A separate issue is the use of Y. pestis for bio-warfare.


Since 1947, there have been 390 cases of Plague in the U.S. resulting in 60 deaths. From 1980-1994 this country has had 229 cases with 33 deaths. The last two Americans to succumb to Plague died in August 1996, both due to transmission by way of prairie dogs. A thirteen year-old Kazakhstani boy died of bubonic Plague on August 9, 1999—the first such death in that country in 25 years. Many other nonfatal cases have been reported.  The last known case of human-to-human transmission occurred in Los Angeles in 1924. As discussed Plague is still present today in the US and is mostly harbored in rodent populations (Sylvatic plague). 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 plague.  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).

Worldwide Distribution of Plague. Image Courtesy of the Center for Disease Control and Prevention.


Fleas and Pets. With very heavy prolonged flea infestations, pets can develop anemia due to the loss of blood.  In extreme cases a pet may harbor an infestation of hundreds of fleas.  In such cases the animal’s immune system can be severely damaged and can even result in death.  These types of infestations are more common in kittens and puppies as they are less capable than adults in physically removing fleas by biting and scratching.


Dogs and cats also may develop allergic reactions to flea bites.  This is especially true in older pets, which have a sustained history of fleas.   As with most allergic reactions they are genetically linked.  It is not uncommon in households with many cats for a few to develop allergies while others harboring approximately the same number of fleas can apparently go unaffected.  In cases of extreme allergic reactions, the animal will lose large amounts of hair, especially around the rump and on the tail.  One of our black cats (we called him old bald butt Bart) develops this condition every flea season.  Such an allergy can develop from the bite of a single flea.  In addition to hair lost, the animal may develop reddened skin and small scabs over much of his or her body.  The latter are due partially to the excessive scratching of the animal.  Normally a veterinarian can correct allergic reactions by injection and oral administration of cortisones and flea control. Unfortunately the over use of cortisones can lead some undesirable side effects. There is a new product that is currently available to veterinarians called apoquel. It minimizes itching in pets with skin allergies including the presence of flea bites.


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 a small child.  Once consumed, the worm form emerges from the cyst and begins to feed in the digestive tract.  Tapeworms 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.


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, flaky dry skin, hair loss especially around the upper rump, and many bumps and scratches due to the pet’s attempts to remove the fleas.  Older animals are typically most susceptible to these allergies.  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. 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).


Typical Cat flea Bites Occurring on Lower Legs.  Image Courtesy of Vopak Inc.


The human flea, Pulex irritans (Figure 14), is found worldwide.  Besides humans, this flea infests cats, dogs and many other animals, particularly pigs. It breeds very commonly in pigsties, and individuals working in such locations can accidentally pick up large numbers of fleas and start infestations in their own homes. The human flea is usually the most common flea in farms. 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.


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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 are known for their ability to jump (over 6 inches high and 13 inches laterally) and for their great strength.  They are said to be able to pull over 400 times their own weight.  The latter fact is especially impressive (if true), because the average human would have a hard time pulling much more than their own weight.  In the circuses, these fleas performed a variety of acrobatic tricks, 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 chigoe, Tunga penetrans  is also known as jiggers, chiggers, chique and sand fleas.  Some of these names can be misleading, as these are not true chiggers, which are of course mites or are they true sand fleas, which are actually crustaceans.  This is a tiny burrowing flea that is found in the tropical areas of Africa, North and South America, and the West Indies. It is said to have inspired the common old sailor saying, “I’ll be jiggered”.


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. The sand flea is typically found in the sandy soil of dry, warm climates. Common habitats include deserts, stables, beaches, stock farms, and close to farms. Even though male and female sand fleas sporadically feed on warm-blooded hosts, it is the pregnant female flea that burrows into the skin resulting in cutaneous lesion. The females does not have any specialized mouthparts for burrowing but simply attaches to the skin by her anchoring mouth and claws and violently burrows into the epidermis. Reportedly this process is painless.  It is thought that the flea releases some type of tissue dissolving enzymes. Subsequent to penetration the female leaves her posterior (rear) end exposed to the skin surface (Figure 17). The "black dot" of the nodule is this posterior end of the flea sticking out. This inflamed opening provides the flea with air and an exit for the feces and eggs. With its head deep below the surface of the skin, the flea feeds on the host's blood and expands up to 1cm in diameter. Over the next few weeks, she lays over 100 eggs which are subsequently released through the exposed opening and fall to the ground. The flea subsequently dies and is slowly absorbed by the host's skin. The eggs hatch on the ground in three to four days. In the next three to four weeks, they pass through their larval and pupal development eventually becoming adults. The complete life cycle of these fleas is about a month. penetrans (1).JPG


Left. Heavy Chigoe Infestation. . Image R. Schuster.  CC BY-SA 3.0. Chigo Removed from Foot. Image Courtesy Phillip Wiegell. CC BY SA 3.0-SA 3.0.


The first indication of infestation by this sand flea is a relatively small black dot on the skin at the point of penetration. Because the flea is a relatively poor jumper, most lesions occur on or near the feet (Figure 18), and more often than not on the soles, the toe webs, and under the toenails. Among natives who frequently squat to defecate or rest, however, the buttocks and scrotal sac can be also involved (ouch). Initially a small, inflammatory papule with a central black dot appears. Within the next few weeks, this papule increase in size forming into a white, pea-sized nodule with well-defined borders. This lesion can be symptomless although in extreme saturations can be pruritic to extremely painful. Multiple/severe infestations may result in a cluster of nodules with a honeycomb appearance. Heavy infestations may lead to severe ulceration, fibrosis and inflammation and more importantly gangrene, loss of toenails, sepsis, auto amputation of the toes, and death may also occur. Fortunately in most cases these lesions heal without further complications. The possibility of secondary infection is quite possible. Tetanus is a common secondary if that has reported. Individual should avoid walking with bare feet where these fleas are known to occur.  Of course dogs and other pets are subject to the attack of these parasites. (Figure 19).




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. 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.  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 even when used properly will only remove 10 to 70% of the adult fleas. This method is also quite time consuming.


Shampoos. These products tend to be a temporary solution to a continuous 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.  However a big disadvantage is that they do not kill the larval stage as it is found off the host. Typically when using a flea shampoos the pet (probably dog as cat wouldn't work so well) l should be thoroughly lathered and then be thoroughly rinsed after 15 minutes.  There are a variety of products available containing different active ingredients.  Pyrethrums are derived from Chrysanthemum flower heads and some consider them a natural product. . 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. I doubt they are used any more do to this fact.  Citrus peel derivatives are used in some shampoo products, which are fairly mild making them useful for use on kittens and puppies. However, in some cases cats may exhibit allergic reactions to these materials. In addition some of the natural products are not as effective as the synthetic are and in some case are more toxic to mammal than the synthetics.  Pennyroyal oil is another natural product used in pet shampoos.  Pulegone, the active ingredient can be toxic to mammals (cats and dogs) if misused resulting several side-effect including death due to liver failure. If used label directions should be followed carefully.


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 of insects including fleas. 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. Another 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).   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. Commercial products for the treatment of flea infestations on pets contain pesticides such as imidacloprid, permethrin, and (S)-methoprene.


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.  Table salt can also be used inside the home in the same way as, or in combination with, baking soda as a low cost and safe method of breaking their life cycle. Pulverizing or grinding the salt with a coffee grinder will make it more effective as it will stick to the flea, killing it quicker through dehydration.


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. The problem with some of these formulations is that fleas have developed considerable resistance to them.  


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. Although possibly effective limitations are that it should be use year around and if there are several animals in the house success if less likely


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