Individuals of this order are characterized by possessing one pair of functional wings (in Latin di= two and pter=wings). The second pair of wings (halteres) is rudimentary, knob-like in appearance, and is thought to be used for balance during flight. This is a large order with many economic forms, including beneficial insects, vectors of disease and crop pests. The adults of many fly species frequently are found nearby in the same environment as the larvae or maggots.

House Flies. The house fly is worldwide in distribution and has a tremendous reproductive capacity. Female flies are each capable of laying several hundred eggs-the record number of eggs is held by a captive female that laid 2,387 eggs in 21 batches. The entire life cycle can be completed in as little as ten days (Figure 20A). Given this type of reproductive capacity, if a pair of flies mated in April and all offspring survived to reproduce, and this cycle were repeated every ten days, by mid August in the same year there would be enough adult flies to cover the earth by 45 feet. Obviously this situation never develops, primarily due to limitation of food, space and natural mortality.

Females will lay their eggs in almost any decaying waste but far prefer animal excrement, especially horse manure.  When horses were the usual mode of transportation in the US house flies were far more abundant than they are today. It was estimated that 90 % of them bred in horse manure. It has been said that Henry Ford was more important in reducing house fly populations in the US than any other person.  His development of mass production of the Model T and Model A Ford automobiles made it possible for the average person to buy a car. As a result the mode of transportation changed and no longer were there piles of horse manure found in everyone’s back yard-hence less flies.

There is a well-document storey in the early twentieth century about a forest ranger in Montana who walked into a local restaurant, looked over the counter and indicated he wanted a piece of the blueberry pie.  The waitress waved her hand over the pie chasing off a hoard of house flies and indicated it was apple. Although somewhat gross the storey exemplifies the importance of sanitation in controlling this species. They are a major nuisance in many areas of the world. This is especially true in third world countries where poor sanitary practices are common. As indicated house fly larvae breed chiefly in decaying plant and animal matter and, considering their reproductive capacity, the main method of house fly control is to prevent or destroy potential breeding sites. Area wide sanitation is important in their control since the adult can fly considerable distance from their breeding source.  In one experiment it was demonstrated that the adults \can move up to 13 miles from their breeding source.

In California and most of the rest of the United States, there are precise health rules dealing with this problem. These rules are aimed at reducing or prevent the breeding sites of these flies (the essential mean of reducing their populations). These include regulation of agricultural practices, landfill management, and practices as simple as requiring covers on garbage cans. The success of breeding site prevention can be seen on the television news almost daily. One need only to watch foreign correspondents reporting from countries that lack these regulations: it's common to see the reporters constantly waving their hands in front of their faces in attempts to 'shoo away' the flies.

These flies are usually no more than a nuisance but may transmit disease causing bacteria and viruses-especially in underdeveloped countries where sanitation is poor. House flies have been implicated in vectoring a number of diseases of humans and other animals. These diseases include typhoid, cholera, yaws, dysentery, polio and food poisoning. The bacteria are transmitted both externally and internally to our food.  When a fly is attracted to feces or our garbage literally several million bacteria can adhere to its tarsi (feet) and other part of its body. In turn when it land on our food these are readily transmitted. If a fly suck moisture or feeds on garbage (again including feces) it digestive system becomes contaminate with germs. If that fly subsequently lands in a sugar bowl or some other solid human food it cannot readily feed on it since flies only feed on liquids.  However it has the capability of liquefying that solid (e.g. sugar). This is accomplished by regurgitating the contents of its digestives system (including digestive enzymes). Once liquefied the sugar is sponged up by the fly’s mouthparts. Of course a certain amount of residue (including germs and other component from the digestive system) are left behind in the sugar bowl. This residue is known as a “fly spot” and appears a small dark spot.

Historically typhoid fever is probably the worst of the diseases that have been transmitted by house flies.  In 1898, during the Spanish- American War, about one fifth of the American soldiers living in encampments contacted this disease which was responsible for approximately 80 percent of all death amongst the troop-including bullets.   Again the bacterium causing this disease was apparently transmitted from the outdoor latrines to their food via house flies.

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Left. Adult House Fly Sponging Up Liquid. Both Images Courtesy Muhammad Mahdi Karim GFDL 1.2. Right. Mating House Flies.

Blowflies. Blowflies are commonly encountered in and around the home. They look like houseflies, but can readily be distinguished by their metallic blue, green, or copper colored bodies. Unlike houseflies, larvae of blowflies breed in rotting or decaying meat. Consequently, they are commonly found in animal carcasses. In the wild they are considered beneficial, as they are the first organisms to begin the natural cycle of animal decay.

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An Adult Blowfly or Green Bottlefly. Image Courtesy Muhammad Mahdi Karim GFDL 1.2

There is an area of law enforcement called forensic entomology. Sometimes it is difficult to determine the time of death for a murder victim by using conventional techniques. In these cases the types of insects found either feeding on the body or associated with it can indicate time of death. Once an animal dies (including humans), there is a predictable sequence of insect species that are attracted to the host (corpse). This sequence starts within a few hours after death and can extend up to several months. Upon examination a forensic entomologist can determine which of these insects are present. Using this information, plus the prevailing temperatures since death, he or she can calculate the approximate time of death.

Blowflies occasionally attack living animals (myiasis). In most cases, the fly deposits her eggs (called a hit) and the hatching larvae feed chiefly on the decaying tissue associated with wounds. This feeding activity rarely harms the animal, and in some cases can actually be beneficial. It was found during World War I that wounded troops who were not found immediately and were left in the battlefield for a few days, developed fewer of certain types of deep-seated infections than did those soldiers taken directly to the hospital. The wounds of the soldiers left in the field were infested with fly maggots, which secreted a material named allantoin, a natural antibiotic. The introduction of blowfly maggots into wounds is still practiced worldwide by many primitive people and the use of sterilized maggots is now receiving some attention by physicians in the United States.

Maggot Therapy. Maggot therapy (also known as maggot debridement therapy (MDT), larval therapy, larva therapy, larvae therapy, biodebridement or biosurgery) is a type of biotherapy involving the intentional introduction of live, disinfected maggots (fly larvae) into the non-healing skin and soft tissue wound(s) of a human or animal for the purposes of selectively cleaning out only the necrotic tissue within a wound (debridement), disinfection, and promotion of wound healing.

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Maggots Feeding in Wound. Left Image Courtesy of PD-USGOV-HHS-NIH-Public Domain. Right. Image Courtesy Alexsey Nosenko / Maggot Medicine CC BY 3.0

Written records have documented that maggots have been used since antiquity as a wound treatment. There are reports of the successful use of maggots for wound healing by Maya Indians and Aboriginal tribes in Australia. There also have been reports of the use of maggot treatment in Renaissance times. During warfare, many military physicians observed that soldiers whose wounds had become colonized with maggots experienced significantly less morbidity and mortality than soldiers whose wounds had not become colonized. These physicians included Napoleon’s Surgeon General, Baron Dominique Larrey, who reported during France's Egyptian campaign in Syria, 1798–1801, that certain species of fly destroyed only dead tissue and had a positive effect on wound healing.

Dr. Joseph Jones, a ranking Confederate medical officer during the American Civil War, is quoted as follows, "I have frequently seen neglected wounds ... filled with maggots ... as far as my experience extends, these worms only destroy dead tissues, and do not injure specifically the well parts." The first therapeutic use of maggots is credited to a second Confederate medical officer Dr. J.F. Zacharias, who reported during the American Civil War that, "Maggots ... in a single day would clean a wound much better than any agents we had at our command ... I am sure I saved many lives by their use." He recorded a high survival rate in patients he treated with maggots.

During World War I, Dr. William S. Baer, an orthopedic surgeon, recognized on the battlefield the efficacy of maggot colonization for healing wounds. He observed one soldier left for several days on the battlefield who had sustained compound fractures of the femur and large flesh wounds of the abdomen and scrotum. When the soldier arrived at the hospital, he had no signs of fever despite the serious nature of his injuries and his prolonged exposure to the elements without food or water. When his clothes were removed, it was seen that "thousands and thousands of maggots filled the entire wounded area." To Dr. Baer's surprise, when these maggots were removed "there was practically no bare bone to be seen and the internal structure of the wounded bone as well as the surrounding parts was entirely covered with most beautiful pink tissue that one could imagine." This case took place at a time when the death rate for compound fractures of the femur was about 75-80%.

While at Johns Hopkins University in 1929, Dr. Baer introduced maggots into 21 patients with intractable chronic osteomyelitis. He observed rapid debridement, reductions in the number of pathogenic organisms, reduced odor levels, alkalinization of wound beds, and ideal rates of healing. All 21 patients' open lesions were completely healed and they were released from the hospital after two months of maggot therapy.

After the publication of Dr. Baer's results in 1931, maggot therapy for wound care became very common, particularly in the United States. The Lederle pharmaceutical company commercially produced "Surgical Maggots", larvae of the green bottle fly, which primarily feed on the necrotic tissue of the living host without attacking living tissue. Between 1930 and 1940, more than 100 medical papers were published on maggot therapy. Medical literature of this time contains many references to the successful use of maggots in chronic or infected wounds including osteomyelitis, abscesses, burns, sub-acute mastoiditis, and chronic empyema.

More than 300 American hospitals employed maggot therapy during the 1940s. The extensive use of maggot therapy prior to World War II was curtailed when the discovery and growing use of penicillin caused it to be deemed outdated. With the advent of antibiotic-resistant bacteria, Dr. Ronald Sherman, a physician previously at the University of California, Irvine, sought to re-introduce maggot therapy into modern medical care. In 1989, he set up fly breeding facilities at the Veterans Affairs Medical Center in Long Beach, California, in order to use maggots for the treatment of wounds. That year, using a Paralyzed Veterans of America Grant, he initiated a prospective controlled clinical trial of maggot therapy for spinal cord patients with pressure ulcers who had failed two or more courses of conventional wound care. The therapeutic maggot used by Sherman is a strain of the green bottle fly (Phaenicia sericata) and marketed under the brand name Medical Maggots.

Over fifty scientific papers have been published that describe the medical use of maggots. Six thousand maggot therapy patients have been included in case histories or other studies. About 400 patients have been documented within clinical studies. In the medical literature, limb salvage rates with maggot therapy are about 40% to 50%. Some report success rates of 70% to 80%.

In a 2007 preliminary trial, maggots were used successfully to treat patients whose wounds were infected with MRSA, a bacterium (Staphylococcus aureus) with resistance to most antibiotics. Some of these strains include "flesh eating bacteria" causing frequent deaths upon infection of deep tissue. In these cases maggots clean up the already dead tissue thus preventing further infection spread.

In 1995, a handful of doctors in 4 countries were using maggot therapy. Today, any physician in the U.S. can prescribe maggot therapy. There are over 800 health care centers in the United States that have utilized maggot therapy. Over 4,000 therapists are using maggot therapy in 20 countries. Approximately 50,000 treatments were applied to wounds in the year 2006.

The use of maggots to clean dead tissue from animal wounds is part of folk medicine in many parts of the world. It is particularly helpful with chronic osteomyelitis, chronic ulcers, and other pus-producing infections that are frequently caused by chafing due to work equipment. Maggot therapy for horses in the United States was re-introduced after a study published in 2003 by veterinarian Dr. Scott Morrison. This therapy is used in horses for conditions such as osteomyelitis secondary to laminitis, sub-solar abscesses leading to osteomyelitis, post-surgical treatment of street-nail procedure for puncture wounds infecting the navicular bursa, canker, non-healing ulcers on the frog, and post-surgical site cleaning for keratoma removal.

Maggots are applied by containing them in a cage-like dressing over the wound for two days. The maggots may be allowed to move freely within that cage, with the wound floor acting as the bottom of the cage; or the maggots may be contained within a sealed pouch, placed on top of the wound. The dressing must be kept air permeable because maggots require oxygen to live. When maggots are satiated, they become substantially larger and seek to leave the site of a wound. Multiple two-day courses of maggot therapy may be administered depending on the severity of the non-healing wound.

Maggots can never reproduce in the wound since they are still in the larval stage and too immature to do so. Reproduction can only occur when they become adult flies and mate.

The maggots have three principal actions reported in the medical literature:

  • Disolving rotting tissue from wounds (debridement);

  • disinfecting the wound by killing bacteria; and

  • stimulating wound healing.

The debridement of necrotic tissue is a prerequisite for successful wound care. If debridement does not take place, wound repair is significantly impaired. Necrotic tissue in the wound is not only an obstacle for localized treatment, but becomes an ideal breeding ground for bacteria and may lead to gangrene, necessitating limb amputation, and potentially fatal sepsis (infection of the blood).

Surgeons cannot be very precise in debriding dead tissue while leaving living tissue. The human eye is simply not very discriminating in identifying healthy tissue from necrotic tissue, and surgeons only have a very limited time to operate while their patient is under anesthesia. Consequently, surgeons use their scalpels to remove far more viable tissue than is needed, producing a wound larger than necessary that has more bleeding and a greater chance of becoming infected. Patients also experience more wound-associated pain after removal of healthy tissue. Wound care therapists can find themselves needing to remove necrotic tissue from a wound day after day, deeper and deeper; this is impractical as surgeons simply do not have the time to perform frequent surgical debridements. The requirement for frequent surgical debridement complicates and lengthens wound healing, lengthening hospital stays and increasing costs.

In maggot therapy, a large number of small maggots selectively consume only necrotic tissue far more precisely than is possible in a normal surgical operation, and can debride a wound in a day or two. These maggots do not damage healthy tissue: they operate with precision at the boundary between healthy and necrotic tissue. They derive nutrients through a process known as "extracorporeal digestion" by secreting a broad spectrum of enzymes that liquefy necrotic tissue, and absorb the semi-liquid result within a few days.

Any wound infection is always a serious medical complication. Infected living tissue cannot heal. If the wound is infected with an antibiotic-resistant bacteria strain, it becomes difficult or impossible to treat the underlying infection and for any healing to occur. Wound infection could further be limb and life-threatening. When maggots successfully debride a necrotic wound, a source of wound infection is removed.

For wounds already infected, maggot therapy is effective even against antibiotic-resistant bacteria. Maggot secretions were first experimentally shown in the 1930s to possess potent antimicrobial activity.  Secretions believed to have broad-spectrum antimicrobial activity include allantoin, ureaphenylacetic acidphenylacetaldehydecalcium carbonate, and proteolytic enzymes. Bacteria not killed by these secretions are subsequently ingested and broken down within the maggots.

In vitro studies have shown that maggots inhibit and destroy a wide range of pathogenic bacteria including methicillin-resistant Staphylococcus aureus (MRSA), group A and B streptococci, and Gram-positive aerobic and anaerobic strains. In a published review of five patients who were infected with MRSA, some having failed conventional therapy for up to 18 months, maggot therapy was able to eliminate the bacterium from all wounds in an average of 4 days.  Maggot therapy therefore represents a highly cost-effective method for managing MRSA infection without exacerbating the problems of antibiotic resistance.

Maggot therapy has been shown by multiple researchers to have wound healing properties. Maggot secretions appear to amplify wound healing. Recent studies have shown that maggot secretions are able to stimulate the growth of human fibroblasts and slow-growing chondrocytes. Chondrocyte proliferation, as well as the synthesis of cartilage-specific type II collagen, increases in the maggot secretion environment. Micromassage of the wound by maggot movement is further thought to stimulate the formation of granulation tissue and wound exudates by the host. The precise mechanism(s) of maggot stimulation of wound healing is an active area of study by several researchers. Maggot secretions also contain a substance called allantoin (also found in many shaving gels) which has a soothing effect on the skin.

There are limitations of maggot therapy. The wound must be of a type which can actually benefit from the application of maggot therapy. A moist, exuding wound with sufficient oxygen supply is a prerequisite. Not all wound-types are suitable: wounds which are dry or open wounds of body cavities do not provide a good environment for maggots to feed. In some cases it may be possible to make a dry wound suitable for larval therapy by moistening it with saline soaks, applied for 48 hours.

Maggots have a short shelf life which prevents long term storage before use.  Patients and doctors may find maggots distasteful, although studies have shown that this does not cause patients to refuse the offer of maggot therapy. Maggots can be enclosed in opaque polymer bags to hide them from sight. Dressings must be designed to prevent any maggots from escaping, while allowing air to get to the maggots. Dressings are also designed to minimize the uncomfortable tickling sensation that the maggots often cause.

Screwworms. There is one group of blowflies that are first attracted to decaying tissue, but then move quickly into healthy tissue—sometimes resulting in the death of animals. The most notorious of this group is the primary screwworm, a species that was eradicated from the United States using the sterile male technique. This blowfly is still a major pest of cattle, ranging from Mexico to South America. Once the larvae begin to feed deeply in healthy tissue, the infested animal becomes weakened and frequently stops feeding, drinking and sometimes dies.

Larvae of Primary Screwworm, a Major Cattle Pest in South America.  Image Courtesy ARS-John Kuchanski.

In many areas of the world human myiasis is fairly common. In one documented case, which occurred in the U.S. prior to eradication of the screwworm, a female fly deposited her eggs up the nostril of a man who had a cold. Apparently, the fly was attracted to his nasal discharge. Upon hatching, the maggots ate their way through the soft pallet and then the hard pallet. During the autopsy over one hundred larvae were removed from the man's brain.

Bot Flies and Cattle Grubs.  These are fairly common pests of cattle and other large mammals.  There are 2 major species of cattle grubs in the United States, namely the northern and common cattle grubs.  These are also known as the heel flies, bomb flies or ox warbles. Anyone who works with cattle is undoubtedly familiar with the large tumor like swellings that develop on the backs of these animals during the winter and early spring months.  If this tumor is squeezed, a large grub-like maggot, about the size of an elongated marble, will pop out.

Common Cattle Grub Occurring Throughout Much of North and South America.  Image Courtesy Marcelo de Campos Pereira, University of San Paolo, Brazil.

The adult flies deposit their eggs on the hairs in the lower legs and heel.  They are not very secretive and frequently buzz loudly in doing so: hence the name bombfly. There is no real pain to the cow during this oviposition process but because of the loud and aggressive nature of this attack the cattle become terror stricken and gallop madly for water or shade.  Once hatched, the larva bores into the skin and internally travels up the legs through the tissues, spends a time in the stomach and finally ends up lodging beneath the skin of the back where it forms large cysts. Soon after reaching the back it cuts a small breathing hole through the skin.  Once fully grown, the mature larva eats its way through the skin and drops to the soil to pupate.  The entire life cycle takes about a year to complete.

Damage from these insects is multifold.  The injury is first irritation caused by the migrating larvae through the animal’s body.  This typically results in weight loss. When the maggots emerge from the back the hide is cut and potential leather ruined.  The sore from these wounds may fester and secondary infection occurs. One major problem is the animal’s reaction to fly oviposition.  Animals are frequently hurt in their attempts to escape. Occasionally a cow will rush off a high cliff in its attempt to escape. Pregnant females have been known to abort.

This fly can also infest humans with symptoms including itching, pain, and cramps and possible blindness or death with the larvae ending up in the chest, neck, brain, spine, and eyes.   The following is a narrative of a human infestation. “Several days after initial infestation, exact time not remembered, soreness was experienced and a slight swelling in the region of the right groin appeared. In about a week the swelling had increased to the width of a hand with no discoloration. The swelling then crept downward toward the left side affecting the scrotum, thence downward along the left leg to the knee and calf, thence back up the left leg following about the same course to the left groin, thence across to the right groin and back again to the left and upward along the left side of the body, slightly anterior to the shoulder, thence downward to the upper right arm to near the elbow, when the arm could not be raised without great pain, thence the swelling traveled upward again to the neighborhood of the shoulder blade where a “hive-like” local swelling was formed without any itching sensation. Mr. C. stated that at this point he was “bothered” all night, and while rubbing his arm and manipulating his shoulder muscles a larva of some insect “popped out”.

Horse Bot Fly. Gasterophilus intestinalis. Worldwide, 9 different species of Gasterophilus exist, primarily affecting horses and donkeys. Three of the more common Gasterophilus species are found in North America. Gasterophilus intestinalis is the more common horse bot fly which is an internal parasite of the gastrointestinal tract. Gasterophilus nasalis, the nose bot fly, and G. haemorrhoidalis, the throat bot fly are also distributed throughout North America. The adult fly is between 2/3 and 3/4 inch in length and resembles a bee with its black and yellow hairs. The adult has small, nonfunctional mouthparts and does not feed. Currently, the horse bot fly, G. intestinalis, is found throughout the world and is one of the main species present in North America. The horse bot fly directly enhances its own dispersal by traveling several miles to find an appropriate host. Dispersal also occurs during larval stages by transport of infested horses.

 

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              Bot Fly Adult. Image Courtesy Georgia Southern University.

 

Horse bot flies undergo complete metamorphosis, including 3 larval instars with one generation per year. The stages of the life cycle are not restricted to certain seasons due to the varied climates found in different geographical locations. However, a general cycle begins with eggs laid in the early summer months. The female can oviposit between 150 and 1000 eggs on a horse's body during the early summer months. Eggs are deposited directly on single hairs of the horse's front legs, abdomen, flanks, and shoulders.

 

Larva hatch from these eggs within 5 days. Larvae are stimulated to emerge by the horse licking or biting fully developed eggs and subsequently crawl to the mouth or are ingested.  They then bury themselves in the tongue, gums, or lining of the mouth and remain for approximately 28 days. After wandering in the mucosa of the mouth, the larvae molt to the second stage and move into the stomach. The second and later third stage larvae typically attach to the lining of the stomach near the junction of the esophageal and cardiac regions. The second and third instar larvae remain immobile and feed for the following 9 to 12 months.

 

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Horse Bot Larvae Feeding on Horses’s Gut.  http://commons.wikimedia.org/wiki/User:Kalume

The third instar larvae are relatively large, from 1/2 to 3/4 inch long and are adapted to life in the gastrointestinal tract with their rounded body, narrow, hooked mouthparts, and spines. The hooked mouthparts enable the larvae to securely attach to the lining of the stomach and intestinal tract. They use their flat mandibles to abrade the tissue of the stomach. Once fully matured, the larvae detach from the gastrointestinal tract and pass from the horse's body in the feces and burrow into the soil or dried manure where they pupate and remain for the next one to two months. This stage of the life cycle occurs between late winter and early spring. Because of horses' behavior to habitually defecate in the same location and the lack of larvae movement, the amount of pupae in fecal piles can become rather significant.

The adult horse bot fly emerges after a 3 to 10 week period during the summer or fall season. Mating follows almost immediately after emerging from the pupae. The mating activity typically occurs in the early afternoon during warm, sunny weather in relative proximity to horses or on hilltops. Mating also is likely to occur around fecal piles where pupae numbers are large thereby greatly increasing the chances of male and female contact upon adult fly emergence. Once the male and female flies meet, they sink to the ground and copulation occurs within 3 to 4 minutes. Within hours, the female seeks a host. Dispersal of eggs by the female is not restricted to one horse but can occur on many horses within an area thus increasing the chance of larval survival. The adult female lifespan lasts 7 to 10 days.

The common host of this particular species of bot fly is the horse. Other equid species, including mules and donkeys, can also serve as hosts. Although accidental, the horse bot also has been reported in man causing either ocular (eye) or coetaneous (skin) myiasis.

 

The horse bot fly occasionally can cause ocular myiasis, or invasion of the eye by first stage larvae. Although these cases are rare, they often occur in individuals handling horses that have bot fly eggs on their hair. Occasionally, these bot fly larvae will enter the eye, rather than reside on the surface as is more common with the sheep nose bot, Oestrus ovis. An additional rare form of horse bot myiasis is cutaneous myiasis. In this case, hatching larvae enter the skin of humans and begin burrowing through the skin causing visible, sinuous, inflamed tracks accompanied by considerable irritation and itching. Anyone working with horses during bot fly season should be familiar with the risks and take appropriate precautions (do not rub eyes after combing or washing animals and wash hands when finished).

Human Bot Fly.  Dermatobia hominis, is a pest of mammals, birds, and humans and is common in Mexico, Central and South America.  The larvae are known as a variety of name including torceli, torsalo and berne.   This is a major pest in Brazil and Central America, where young, heavily infested animals may be killed and in cattle the loss of meat, hides and milk has at times severely crippled this industry.  In humans, various parts of the body can be infested, including arms, legs, back, scrotum and buttocks.

The life history of this fly is quite unique.  The females does not deposit her eggs on the primary host, but seeks out and captures a mosquito, fly or other arthropod and glues her eggs on this critter.  The main carrier is a large day-flying species of mosquito. Over 48 species of other flies (mosquitoes, black flies, deer flies and others) and one species of tick have also been implicated in this cycle.  The eggs are attached to the carrier so the top end points downward. Then when the carrier makes contact with a potential host, the larvae can immediately emerge and are in an optimum position for attachment.  When the mosquito begins to feed on its host the fly larvae emerge from the eggs and bores into the skin, penetrating the subcutaneous areas. The larval period in the body is about 6 weeks--at the end of which it bores out, drops to the ground and pupates.

An acquaintance of mine was recently working in Costa Rica and unknowingly acquired one of these larvae.  For the first few weeks he wasn’t aware of the infestation but eventually noticed a small cone shaped protrusion periodically appearing on his belly.  This protrusion was the breathing tube of the maggot rising to the surface of the skin in order to breathe. He eventually realized that there was a human bot maggot feeding in this area.  He wasn’t overly concerned (being a weird entomologist) as there wasn’t any significant pain and decided to name his maggot George. Things remained the same for a few more weeks and he was actually excited and hoped that he would eventually see the maggot emerged from his body.  A few weeks later he woke up with extreme pain in this area. Obviously the maggot was getting bigger and was doing significant damage. All the sudden he decided that he better do something about this parasite. An individual from one of the organizations dealing with tropical medicine suggested one cure was to place a large steak tightly over the belly in the affected area.  The reasoning was that when the maggot rose to the skin surface to breath it would have to leave the body through the steak to obtain oxygen. He tried it-didn’t work! The next suggestion was to smear the area with Vaseline thus preventing the maggot from breathing. After a few more unsuccessful remedies he has the one inch maggot removed by surgery. He keeps it in jar of alcohol.

Right. A Common Fly Carrying the Eggs of the Human Bot fly.  Image Courtesy of University of Sau Paulo, Brazil. Left. A Human Bot Fly Larva Extracted from Host (Human). Image Courtesy University Nebraska.

One scientist allowed 2 human bots to enter his skin and reported the following.  “I allowed 2 larvae to bore into the skin on my arm. The first required 42 minutes and the second 1 hour and 35 minutes.  I felt no sensation for the majority of the time but as the larvae were disappearing below the skin I felt a sharp pricking.  At first there was a sharp itching at night but within a few days lesions developed which looked like boils and by the end of 3 weeks they were excruciatingly painful.  After about 50 days the large larvae emerged and dropped from the skin. No pain was felt at the time of emergence”.

I was in Costa Rica a few years ago and had a fly land on me leaving one of these maggots on my skin.  I watch it a while as it began to eat into my body. Even though I like to document this type of stuff I decided that I was not that dedicated and eliminated the pest.  That reminds me of a related situation we ran across on a student trip to Malaysia. In the some of the forest they have leaches which actually travel over the ground with a looping movement much like that of an inch worm.  I collected one thinking it was an inch worm but on close inspections I noticed it was not as it began to burrow into my skin. I subsequently alerted the students of the presence of these and of course their reaction was not that of a normal person.  They (the males) collected their own and tried to get the leaches to feed on them. As you might have suspected by now entomologist for the most part are a weird breed, except for me of course!

Blood Sucking Maggots. Blood sucking maggots are even more disgusting than the human bot fly.  These occur throughout much of Africa and are commonly found in homes. The eggs are deposited in various situations, such as sleeping mats on the ground, in cracks and crevices and other situations where the maggots can find food when they hatch.  The larvae are remarkably resistant to drying out. They are nocturnal, sucking the blood of sleeping people. They produce a wound with their powerful mouth hooks and feed nightly for 15 to 20 minutes when a host is available. The bite of the maggot is felt as little more than a pinprick.  The effect of the bite is quite variable depending on the individual’s sensitivity and their attitude about maggots sucking their blood.

Horse Flies, Tabanus spp, and Deer Flies, Chrysops spp.  These are cosmopolitan in distribution with deer flies typically found at higher elevations. This is a family of large to very large flies that can readily be identified by the shape of their antennae (frequently sickle shaped) and large bulging eyes.  Both types attack large mammals including humans. Only the female is a blood feeder with the male feeding primarily on nectar.  The bite of these flies is painful, due to the lacerating mouthparts.  The fly creates a wound and then laps up the blood.  Although mainly a nuisance to humans, large animals lack the ability to avoid the bites of these persistent creatures.  Under certain conditions the loss of blood due to consistent feeding by a large number of flies can become a major problem. Scientists have recorded over 1,000 horse flies feeding on a single cow over an 8-hour period. The amount of blood loss in this situation would amount to a little over a gallon. These flies have been known to vector anthrax (Bacillus anthracis) as well as tularemia (Francisella tularensis).  Anthrax can be mild if only lesions form on the skin, but can be serious if the spores are inhaled or ingested.  Tularemia causes a high fever, swollen lymph glands, septicemia, and lung infection

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.    An Adult Horse Fly.  Image Courtesy Dennis Ray-Attribution-Share Alike 2.5 Generic

Mediterranean Fruitfly. This is a group of well-known flies that pose serious threats to California agriculture. The most notorious of these include the Mediterranean, Oriental and Mexican fruitflies. None of these three flies are presently established in the continental United States, but all have been accidentally introduced on several occasions only to face eradication attempts by the State and U.S. Departments of Agriculture. On occasion these infestations have been widespread and encompass several counties.

The possible establishment of these and other exotic fruitflies in California or other states creates an enormous threat to agriculture. Fruitflies are primary pests because they attack fruit instead of the crop parts that aren't harvested: such as leaves stems and roots. This is compounded by the fact that they are capable of attacking many different types of crops: the Medfly (Figue 20B) has over 200 known hosts. The reproductive capacity of Medflies is tremendous, much like that of the housefly. Consequently, their population would explode if they were to become well established—with heavy infestations quite likely.

Finally, much of our produce is sold abroad at a premium price to countries where these fruitflies do not now occur (e.g., Japan); it is quite likely that if any of these flies were to be established here, these countries would quarantine our produce.

With this in mind, the California Department of Agriculture has a rather extensive program to prevent these pests from becoming established in the state. The initial phase of the program consists of attempts to prevent the accidental introduction of fruitflies. Any foreign produce, which might contain fruitfly maggots, is inspected closely and/or quarantined. This includes not only commercial produce, but also accidental introduction by individuals traveling. People found carrying undeclared fruit in their luggage upon returning from a country where fruitflies occur (most tropical countries), would face an automatic fine. U.S. Customs has a well-developed inspection procedure for detecting infested fruit and officers are diligent in enforcing these regulations. One of these tools includes the use of beagles and other breeds of dog that have been trained to sniff out luggage containing fruit (the beagle brigade).  They are very efficient and can detect a piece of fruit the size of a small seed located deep in luggage. Of course they are also trained to detect drugs. X-ray machines are used to search suspected luggage.

One year we were returning from a trip to Thailand and coming back were stopped by The Department of Agriculture for luggage inspection. They always stop us since we have been “caught” bringing back some of the larger living Thai insects (giant stag beetles, leaf insects) for use at the University. In doing so I was then placed on their hit list. These had no potential of becoming pests since they were males and obviously could not reproduce. Regardless, they complicated the specimens. When they do this, they then send then send critters to other agents (identifiers) that determine the species. To make a long storey short, the identifiers were my ex-students and they returned the critters to me. On a subsequent trip when returning from Indonesia we were again stopped by agriculture. They ran our luggage through X-ray. The operator rather loudly announced “we have a problem here”. On examination he found a small bag of mangosteen fruit that she accidentally packed. He grabbed our passports until we paid a fine.  

The second phase of the fruitfly prevention program consists of detection of initial infestations. This is accomplished mainly by the use of traps baited with pheromone-like chemicals attractive to the adult flies. Thousands of these traps are placed at strategic locations throughout the state in the attempt to detect an initial infestation before it becomes widespread. Common locations for trap placement are around airports and throughout communities. Individual homeowners with fruit trees are often called upon to allow such monitoring of their trees.

Once an initial infestation is found and its borders are established, eradication attempts are initiated. Quarantine borders are quickly established around the infestation in the attempt to prevent the spread of flies by either commercial or private movement of infested fruit. Signs are posted on freeways and other streets to indicate zones of infested areas and to announce that fruit cannot legally be transported from those areas.

In 1990, a Medfly infestation spread over several counties of Southern California. The primary means of eradication consisted of malathion bait-spray applied by helicopters. The spray consisted of a small amount of malathion mixed with corn syrup and egg whites, which serve as a feeding attractant to the adult flies. This material was applied at the rate of two ounces per acre over a large geographical area. Sprays were applied at night, which upset many homeowners, as the helicopters flew only a few hundred yards off the ground and were quite noisy and intrusive. Also, there were many complaints associated with the formulation, including poisonings and a variety of ill effects on humans, such as skin irritations, nausea and headaches. Many people were very concerned about the possible long-term effect of malathion exposure.

However, almost all of these complaints proved to be unfounded. Malathion has been used for over 30 years as a backyard spray and for a variety of other uses, and has an excellent record as being a relatively 'safe' pesticide. When formulated as a bait spray, malathion is about as toxic to humans as laundry detergent. It should be mentioned that some individuals did experience a temporary nausea immediately after the helicopter applications of this material. It is well documented that malathion bait-spray did cause mild etching on certain types of automobile paint; consequently, homeowners were advised to cover their cars on nights when applications were scheduled.

 

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Adult Mediterranean Fruitfly. Image Courtesy Alvesgaspar (talk) CC BY-SA 3.0.

An alternative to a malathion bait spraying is the sterile male technique. This consists of raising huge numbers of Medflies in a laboratory. The male pupae are exposed to cobalt 60 gamma radiation. As a result of this exposure, at least one dominant lethal mutation develops in the genes of the sperm in the developing pupa's testes. The basic concept is to release huge number of sterile males in the infested area. This greatly decreases the chance of a "natural" male mating with a naturally occurring female and maximizes the chance that the females will mate with sterile males instead. If this occurs, females will not be able to produce offspring due to the dominant lethal gene carried by the sterilized males' sperm. Releases are weekly and eventually the sterile-male-to-natural-male ratio increases. This decreases the chance that a natural male will mate with a natural female and eventually the species is eradicated. This technique has proven to be very effective.

It was not possible to use this method as an alternative to the bait-spraying program in 1990, because the initial infestation was widespread and there were not enough sterile males available to be effective. Since that time, the USDA has established a huge sterile male rearing laboratory in Hawaii.

Frequently bait-spray treatments and sterile male release programs are used together. Initially the natural population may be reduced with several applications of bait-spray which ensures a high sterile-male-to-natural-male ratio with the subsequent release of irradiated males.

Mosquitoes. These are not only nuisance pests, but are extremely important in vectoring a number of diseases in humans and other animals. These small flies can be recognized by their elongate beak-like mouthparts, delicate bodies and scaled wings (Figure 20C).

Mosquitoes, as do all flies, have complete metamorphosis. Most of the eggs are deposited singly or in rafts on the top of water or aquatic plants. The larval stage is called a wriggler (Figure 20C) and feeds by filtering out microorganisms from water. While at rest, one hangs down from the surface of the water and breathes through a tube-like structure protruding above the water surface. The pupa (tumbler) is unique in the insect world in that it is active. It also hangs from the surface and breathes through a tube on the top of its thorax.

The mating behavior of mosquitoes is unique as is that of many insects.  The males typically gather together in large mating swarms, usually at dusk.  I once encounter one of these mating swarms in a cotton field next to an irrigation canal filled with mosquito wrigglers.  The swarm of a few thousand of formed over my head. The annoying but interesting fact was the swarm which was about 4 feet in diameter followed (directly overhead) me as I passed through the field.  The only way I eventually avoided the swarm was when I passed by a small tree that was a foot or two taller than myself at which point it switched to the tree. Even more amazing after I caught over 900 of the mosquitoes with a quick sweep of my insect net only 2 were females.  Apparently the females are individually attracted to and fly directly into the swarm and are immediately pounced on by a male. The pair then mates with the male subsequently returning to the swarm and the female flying away. Apparently a male can recognized a female in the swarming mass of critter by the distinctively different tone of her rapidly vibrating wings.  This has been demonstrated in laboratory experiments where cages males are readily attracted to the tone of a tuning fork that vibrates at the same frequency of that a flying female mosquito of the same species.

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  Right. Adult Female Mosquito.  Image Courtesy Alvesgaspar (talk) GNU Free Documentation.  Left. Mosquito Larvae and Pupa. Image Courtesy CDC Healthwise Photo Library-James Gathaway.                                                                                                  

Some mosquitoes have some of the fastest life cycles in the insect world. Total development occurs in some desert species in as little as three days. Because one female can deposit up to 200 eggs, mosquito infestation can develop quite rapidly. Common sources of mosquito breeding in cities include abandoned or neglected swimming pools or any other sources of standing water. One neglected pool can produce hundreds of thousands of mosquitoes per week.

Females of many mosquito species are bloodsuckers and their bites are rarely felt. As with most blood sucking insects, upon penetration of the skin, saliva is injected which contains an anticoagulant and anesthetic. As a result of these chemicals, the well-known red welt develops at the site of the bite. As with many other parasitic insects, a female mosquito is attracted by the carbon dioxide from the host's breath. Male mosquito adults do not 'suck blood,' but are nectar feeders.

There are many species (approximately 3000) where neither the male nor female do not suck blood but again feed on nectar or other sweet materials.  There is even on group of mosquitoes that beg or “trick” ants for the honeydew they in turn receive from aphids and other insects (see aphids). Many species ants will readily share their recently collected honeydew with other ants of the same species as they travel along their trails to and from their food source-in this case honeydew producing aphids. The mosquito in question merely flies above a trail of ants and drop down hovering directly over and begs individual ants for a handout.  A percentage of the ants will readily regurgitate the liquid which the mosquito immediately sucks up. Others ignore the mosquito which in turn moves on looking for an obliging benefactor.

Yellow Fever. Yellow fever is a viral disease transmitted by infected mosquitoes, mainly Aedes aegypti. The "yellow" in the name refers to the jaundice that affects some patients. There is no cure for yellow fever. Treatment is symptomatic, aimed at reducing the symptoms for the comfort of the patient. Vaccination is the single most important preventive measure against yellow fever. The vaccine is safe, affordable and highly effective, and appears to provide protection for 30–35 years or more. The vaccine provides effective immunity within one week for 95% of persons vaccinated.

History-The effects of yellow fever on humanity, although certainly not as detrimental as malaria or plague, are significant.  It is well known that this disease had a profound effect on building of the Panama Canal. By the time the United States took control of the Panama Canal project on May 4, 1904, the Isthmus of Panama was notorious for the terrible problem of tropical diseases. It is estimated that 12,000 workers had died during the construction of the Panama Railway, and 22,000 during the French effort to build the canal. Many of these deaths were due to disease, particularly yellow fever and malaria. At several times, construction on the Panama Railway had actually halted due to the lack of any healthy workers. It was clear to the organizers of the American effort that previous efforts at disease control had been largely ineffective, as the causes of the two main diseases were unknown, but in 1897 it was proved by Britain's Ronald Ross in India that malaria was treatable.

Although primarily considered a disease of tropical countries there are even numerous records of epidemics of this disease in the U.S. Philadelphia believe it or not. The following account was taken from Short History of Yellow Fever in the US by Bob Arnbeck. From 1793 to 1822 yellow fever was one of the most dreaded diseases in the port cities of the United States. Statistically, one can dismiss it as inconsequential in comparison to tuberculosis and smallpox. Yellow fever did not kill that many people, but during that period, it struck with such ferocity in principal cities that it spread gloom and fear throughout the country. Doctors were uncertain of the cause of yellow fever and the factors that led it to reach epidemic proportions. That uncertainty was not unique. The causes of other diseases were also unknown. But doctors and patients then had an acute understanding of fever. Today, fever is a symptom that can usually be controlled with over-the-counter medicines. Then, fever was tantamount to disease itself. Fever was far more than a question of body temperature and discomfort. It was a state in which a person's whole being was reordered. Two hundred years ago it was conceived in much the same way that we conceive of cancers. Just as today, when one discusses cancer, death is possibly assumed to be a likely consequence, and then when one discussed fever, death was assumed to be a likely consequence. It was this view of morbidity that made yellow fever so feared simply because in the experience of these people who were so sensitive to fevers, yellow fever was most powerful and horrible.

Malaria.  Blood sucking female mosquitoes can vector many diseases to humans including malaria, yellow fever, dengue and encephalitis. Malaria is by far the most important of these diseases. Historically, this disease has killed more humans than any other illness or war. This statement is even more astonishing when it is considered that most types of malaria are not fatal. Once contracted, malaria is a long-term disease characterized by intermittent cycles of chills and fever.

The presence of this disease has actually retarded the growth of certain regions and, sometimes, entire countries. With most types of malaria, the effects are not death; however, the victim becomes lethargic and loses much of the ability to work for over twenty years. Consequently, when most of the human population of a given area has this disease, that region will not develop due to the lack of a work force.

Malaria has shaped the course of history for millennia. It has always been part of the ups and downs of nations; of wars and of upheavals. Kings, popes, and military leaders were struck down in their prime by malaria [See below]. Many great warriors succumbed to malaria after returning from the warfront and advance of armies into continents was prevented by malaria. In many conflicts, more troops were killed by malaria than in combat. The activities of the armed forces would create thousands of breeding places for the vector mosquitoes and thus greatly increase the transmission. Even in recent years, night vigils and other activities like cine-viewing, lack of mosquito nets and other protection, failure to take chemoprophylaxis, due mainly to its adverse effects has contributed to the rising cases of malaria in war time.

 During World War I (1914–1918) in Macedonia, British, French, and German armies were immobilized for 3 years by malaria. On one occasion, when the French commanding general was ordered to attack, he replied: "Regret that my army is in hospital with malaria." Nearly 80 percent of 120,000 French troops in this area were hospitalized with malaria. In an average British strength of 124,000, there were 162,512 admissions to hospital for malaria during the years 1916 to 1918, in contrast to 23,762 killed, wounded, prisoner, and missing in action. In the spring of 1918, about 25,000 British soldiers were sent home from Macedonia with chronic malaria, and, apart from these evacuees, over 2,000,000 man-days were lost to the British Army in this area in 1918 because of malaria. Approximately 7.5/1,000 Americans quartered in the U.S. were infected with malaria in 1917.

 

In World War II: Many troops had to suffer casualties by inflicted malaria even in World War II. Gen. Douglas MacArthur's predicament in May 1943 is very clear: "This will be a long war if for every division I have facing the enemy I must count on a second division in hospital with malaria and a third division convalescing from this debilitating disease!" It appears that the general was not at all worried about defeating the Japanese, but was greatly concerned about the failure to defeat the Anopheles mosquito! 60,000 U.S. troops died in Africa and the South Pacific from malaria. U.S. Forces could succeed only after organizing a successful attack on malaria.

 

In the Korean War (1950–1953): U.S. military hospitals were inundated with cases of malaria, with as many as 629 cases per week. More than 3,000 cases of malaria were documented in U.S. troops that served during the war.

 

In the Vietnam War (1962–1975): Malaria felled more combatants during the war than bullets. The disease reduced the combat strength of some units by half. Over 40,000 cases of Malaria were reported in US Army troops alone between 1965 and 70 with 78 deaths. The U.S. Army established a malaria drug research program when U.S. troops first encountered drug resistant malaria during the war. In 1967, the Chinese scientists set up Project 523 - a secret military project- to help the Vietnamese military defeat malaria by developing anti-malarial formulations.

 

Operation Restore Hope (1992–1994): Malaria was the No. 1 cause of casualties among US troops during the operation. From the time of deployment through April 1993, malaria was diagnosed in 48 military personnel. Malaria was diagnosed in 83 military personnel (21 Marine and 62 Army) following their return from Somalia.

Malaria in Afghanistan, Iraq, and Liberia (2001–2003): Many US soldiers in Iraq walked while eating just to avoid being bitten and infected by mosquitoes. In October 2001, a falciparum malaria epidemic that erupted in Afghanistan claimed 53 lives. When 290 marines went ashore in Liberia in September 2003, 80 contracted malaria. Of the 157 troops who spent at least one night ashore, 69 became infected. In Liberia, over a third of U.S. Marines sent in as military advisors to oversee a civil transition have contracted malaria.

 

After World War II, the World Health Organization (WHO), a part of the United Nations, established a large-scale program that attempted to eradicate malaria from the world. The program did not attempt to kill all mosquitoes, but instead aimed at breaking the disease cycle. It was well documented that almost all cases of malaria were initially contacted in villages. It is also known that if a mosquito bites a diseased person, there is a two-week period prior to the time the mosquito is capable of transmitting the disease causing organisms to another person. During this two-week period, these mosquitoes are almost always found in close association with humans—most frequently sitting on the inside walls of the home.

The technique the W.H.O. developed consisted of spraying a 10%DDT solution on the walls. Of course, with this technique, the residue on the walls kills those mosquitoes that are directly involved in malarial transmission. This technique was extremely successful and the W.H.O., by the mid-1960's, had eradicated malaria from two-thirds of the world where it had previously occurred. However, since that time, many of the mosquito species that vectored this disease have developed resistance to DDT.

As with any large scale program the unexpected occasionally arises.  When DDT was applied to the walls of a remote village in Papua New Guinea several totally unforeseen results unfolded.  Many of the poisoned mosquitoes were consumed by the geckos that are common to homes in many tropical countries. Of course the DDT was stored in the fat of the geckos which were in turn consumed by the village domestic cats.  As a result even a higher concentration of DDT built up in the cat population eventually killing many. A further consequence because many cats were eliminated, the wild rat population began to explode since they were no longer controlled by the cats.  Of course rats harbor fleas which vector bubonic plague and this disease all of the sudden appeared in many of the villagers. One solution to the problem was to parachute cats into the village to attempt to control the rats and reduce the plague problems.

 

If that wasn’t enough the walls and ceiling of the village huts began to collapse within a few month after the initial treatment with DDT.  Apparently there was a wood boring beetle that attacked the wooden framework of the huts. The populations of these beetles were normally kept in check by a parasitic wasp; however, these wasps were very susceptible to DDT thus killing the natural control of these wood destroying beetles.

For a number of reasons, the W.H.O. has not found an adequate insecticide to replace DDT in the program. Because of this, malaria is on a tremendous worldwide comeback. For example, fifteen years ago there were less than one hundred new cases of malaria in Thailand. Last year there were over 250,000 new cases. The situation is the same in most other tropical countries of the world. Last year over a million babies died from malaria.

When visiting a foreign country it is advisable to check with a U.S. county health department as to which type of shots and preventative measures to take. If possible, it is also advisable to check with the health department of the country to be visited. The authors recently visited Thailand and, in checking with three different health departments in the U.S., received three different recommendations– ranging from the taking of four different series of shots plus malaria pills to no shots or malarial preventative pills. The Thai authorities suggested taking nothing. They stated that the strain of malaria causing organisms in Thailand were resistant to the 'malaria pill.' Actually, they indicated that taking the malarial preventative pills might actually increase one's chances of contracting this disease. Malarial pills affect the kidneys and may lower one's immunity system. Their recommendation was to stay out of the areas where malaria is known to occur, remain indoors in the evening hours and wear mosquito repellents.

West Nile Virus. West Nile encephalitis is an infection of the brain that is caused by a virus known as the West Nile virus. First identified in Uganda in 1937, the virus is commonly found in Africa, West Asia, and the Middle East. "Encephalitis" means inflammation of the brain. One of the causes of encephalitis is viral and bacterial infections, including viral infections transmitted by mosquitoes. West Nile virus had not been previously reported in the U.S. prior to an outbreak in New York in September 1999. According to the U.S. Centers for Disease Control and Prevention (CDC), there were 4,261 cases of disease caused by the West Nile virus internationally in 2006; however, the CDC says case reports are understated and estimates that there were 42,000 cases, most of which were unreported. West Nile virus also is called West Nile fever or West Nile encephalitis.

To date, the West Nile virus has been commonly found in humans, birds, and other vertebrate animals in Africa, Eastern Europe, West Asia, and the Middle East. Prior to 1999, the West Nile virus had not been recognized in the Western Hemisphere. The source of the outbreak in New York was probably the Middle East. The American strain of the virus is almost indistinguishable from a virulent strain found in a goose on an Israeli farm in 1998. Thousands of people travel between New York and the Middle East each year. The virus may have hitchhiked a ride to New York.  Mosquitoes become infected by feeding on birds that are infected with the virus. The infected birds may or may not become ill. The birds are vectors. A vector is an intermediate carrier of the virus that is important for the virus' life cycle and transmission cycle. Crows are the birds that are most vulnerable to infection by the West Nile virus. They are often killed by the virus. Although 17 species of birds have been found to be infected by the virus, the common dust-colored house sparrow is probably a principal bird reservoir for the virus in New York. Sparrows can harbor the virus for five days or more at levels high enough to infect mosquitoes that bite them. In turn humans are infected with the West Nile virus from the bite of a mosquito (primarily the Culex pipiens mosquito) that is infected with the West Nile virus.

Crows are the birds that are most vulnerable to infection by the West Nile virus. They are often killed by the virus. Although 17 species of birds have been found to be infected by the virus, the common dust-colored house sparrow is probably a principal bird reservoir for the virus in New York. Sparrows can harbor the virus for five days or more at levels high enough to infect mosquitoes that bite them.

The Eye Gnat. Hippelates collusor and H. pusio are small flies (slightly larger than a grain of sand) that are attracted to mucous secretions of the eye.  These flies do not bite, but persistently feed on eye secretion.  They approach their mammalian hosts, commonly including humans, quietly alighting some distance from their feeding site.  To reach this site they crawl over the skin or take short repeated flights thus adding to the host’s annoyance. I’m getting annoyed just thinking about it! The eye gnats breed in decaying vegetation, manure, and loose sandy soil.  They have been implicated in the spreading of "pink eye" (conjunctivitis).  They are quite common throughout much of the southern United States ranging from California to Florida.  They are found in high numbers in the Coachella Valley of Southern California and prefer hot temperatures.

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Eye Gnat.  Image Courtesy James Lindsey at Ecology of Commanster CC BY_SA 3.0.

Crane Flies.  This is a common group of large long-legged flies which is occasionally confused with mosquitoes. Most crane flies are considerably larger than, and lack the elongated beak (piercing-sucking mouthparts) of mosquitoes. Cranefly adults are nocturnal and readily attracted to lights. Consequently, they are frequently found around porch lights and will occasionally become trapped indoors. The adults are harmless and feed chiefly on nectar. The larvae are aquatic and feed on decaying plants.

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Right. Adult Crane Flies-Commonly Confused with but Easily Distinguishable From Mosquitoes. Image Courtesy Alvesgaspar CC BY-SA 3.0. Left. Image Indicating Non-biting Mouthparts. Courtesy Thomas Shahan CC BY 2.0

 

Stalk-Eyed Flies. These have to be one of the strangest looking groups of insects.  As shown in Figure 20I the compound eyes of this fly are located on elongated stalks with (in some species) the distance between individual eyes exceeding the entire length of their body.  These tiny flies occur primarily in Africa and Asia.

The function and advantage of ocular arrangement apparently is several fold.  When disturbed or threatened this arrangement could be to their disadvantage since rapid flight or takeoff could be cumbersome since due to their “top-heavy” anatomy.  Instead of immediately taking flight the flies curl their leg under their body and fall to the ground. The eye structure is so large that it provided a considerable degree of air resistance and consequently functions as a parachute (or helicopter) allowing the fly to float gently to the forest floor. In addition the distance between individual eyes provides these flies with tremendous peripheral vision allowing them to see in almost all directions while sitting in one position and not needing to move their head.

Most interestingly the distance between the eyes plays an important role in the mating behavior of these flies.  In most species only the males exhibit this extreme arrangement of the eyes with the females exhibiting greatly reduced stalks (when compared to those of the male).  Typically a dominant male will stake out a territory on leaves or other structures and is frequently accompanied by several smaller females. He continuously patrols his territory searching for other male. If a competitive male is encountered then a “mock” battle unfolds.

The opposing males face off (eye to eye) spread their front legs while simultaneously rising up on their hind legs.  This is followed by shaking from side to side, beating of their abdomen on the leaf surface and periodic pumping of their wings. Seemingly the males are comparing the distance their eyes and typically the male with the shortest eye spread submits and leaves.  It has also been determined the female stalk-eyed flies mate more readily and frequently with males that have the widest distance between their eyes-beauty is in the eye of the beholder!

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A Stalk-eyed Fly. Left Image Courtesy Hauke Koch (Karmesinkoenig on de.wikipedia.CC BY-SA 2.0Right. Image Courtesy Rob Knell Creative Commons Attribution ShareAlike 1.0 License

Dance Flies. These are a group of predatory flies that has exhibit courting and subsequent mating behaviors that in some aspects are human-like in nature.  They get their name for the fact that they frequently are found in male/female swarms that undulate up and down in a more or less rhythmic manner-they take them dancing first.  However, if the female seem reluctant to mate a male can frequently entice a female by giving her a gift. In this case he catches a prey (some type of smaller insect) that he presents to her which she may or may not accept-if accept mating quickly follows.  In some species this prey is actually gift wrapped. The male produces silky material that he spins into a balloon enclosing the prey. There are other species that produce the silken balloon but do not include a prey, thus tricking a receptive female into mating.

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Dance Fly.  Image Courtesy André Karwath Aka CC BY-SA 2.5

    No-seeums and Punkies. These are very tiny, blood sucking flies that can be troublesome to humans.  The name no-seeum refers to the fact that the smaller forms can pass through the holes in a window screen and are difficult to see.  The larval stage of these flies is typically semi-aquatic to aquatic or at least they breed in moist soil; common breeding sites include salt or fresh water, tree holes, decaying plant material such as cactus, banana leaves and moist sandy soil.

These tiny flies become major problems in recreational areas, especially in coastal areas around fresh water inlets and tidewater pools, and in mountain areas, where they become so common that they drive tourists out.  The bites of this blood-sucking flies cause itching in sensitive individuals and welt and lesions that may persist for up to a week or more.

We once took a student group down to San Blas, a jungle community along the Coast of Mexico.  One of the participants drank several beers before retiring (passing out) on an outdoor hammock wearing nothing but a swimming suit. When he awakened the next day the punkies had had a field day.  His entire body was covered with the bites of these flies, an average of 13 per square inch. To say the least he was pretty miserable for several days. These flies can vector pathogenic nematodes, protozoans, and viruses.   Control includes painting screens with insecticides and draining their breeding sites.

 

The New Zealand Glow-Worm.  To tell the truth I had never heard of the famous New Zealand glow-worm until we took a group of entomology students to New Zealand (one of the many trips funded by our insect fair at Cal Poly). Unlike the glow worm that we have in the United States and Europe (female adults of phengodid beetles) these are the larval stages of a fly.  They are widely distributed throughout both the south and north island of New Zealand. You can go out in most backyards and find a few. However, they are most commonly found in damp dark caves. In these situation they are found in immense number producing a scene if impressive beauty. These tiny larvae produce a web of fine threads (up to several-foot threads per larva) which are coated with a globular sticky material (appear like a string of pearls).  The larvae are typically found within a central tube from which it can easily reach any of the treads. The light producing organ is located in the terminal abdominal segment and serves to attract other insects (mainly small flies) which in turn are snared by the sticky globules. Once detected the glow-worm slowly reels in the catch by a twisting motion of the front part of the body, as if it were winding the tread around its thorax.

 

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New Zealand Gloworms. Image Courtesy Markrosenrosen. GNU Free Doccumentation

 

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