FAMILY-HIPPOBOSCIDAE-LOUSE FLIES
This is a very strange looking group of ectoparasitic flies. They are easily distinguished by their flattened, leather-like bodies. Most are wingless and all possess beaklike mouthparts for sucking the blood of their host. As indicated they live externally on their host which depending on species is either birds or mammals.
An adult sheep ked. Image courtesy of Marcelo Campos de Pereira.
Sheep Ked-Melophagus ovinus. This is a brown, hairy fly that resembles a tick. This fly is native to most of Europe including Iceland, and the Faroe Islands, as well as North West Africa, Mongolia, and North India. It has been introduced and established in Kenya, South Africa, Japan, Australia, New Zealand, most of North America, and many parts of South America including Tristan ad Cunha and the Falkland Islands. As its name implies the primary host of M. ovinus is the domestic sheep occluding their whole lives in the wool. Sheep ked are most commonly found on the neck, shoulders and underbelly of the host animal.
Sheep ked lives for typically 4 to six months, in this time they may produce from 10 to 20 larvae. A single egg hatches within and the resultant larva remains in the female fly until it is ready to pupate. The larva feeds on the secretions of a milk gland in the uterus of the female. After three larval instars, a white pre-pupa which immediately forms a hard dark puparium. This is deposited on the wool of the sheep and is attached with a glue-like material. This pupal stage lasts for 19 to 23 days in the summer and 20 to 36 days in the winter. Pupal stages are not susceptible to insecticides. If removed from the host, the adult live for 7–10 days.
It has been indicated by experiments that the sheep ked is capable of transmitting bluetongue virus in sheep, though there is little evidence that they are bluetongue disease vectors in nature. In lambs the sheep ked may cause anemia and reduce weight gain. Adults feed on the blood of its host and therefore cause irritation to the sheep, leading it to rub, producing both loss and damage of the wool. It also makes firm, hard nodules that develop on the skin called a cockle which will reduce the value of the hide. The ked feces also stains wool reducing its value. They also transmit Trypanosoma melophagium nonpathogenic protozoan parasite of sheep.
Several insecticides registered for control of sheep keds on sheep. Diazinon and permethrins are both labeled for low pressure spray (knapsack sprayer) and sprinkling can applications. These work well for small flock owners. A number of other products, particularly for commercial operators, are available. Sheep can be sprayed, sprinkled, dipped, or dusted. The best time to treat sheep is in spring, after shearing, when the wool is short and shear cuts have healed. Sheep sprayed during cold weather are more subject to stress. If liquid treatments are used, drying time before evening should be allowed. When daytime temperatures are below 40°F animals should not be sprayed.
Sheep keds can be easily controlled in small farm flocks by attaching a dust bag in a single barn opening used by the flock. Dust bags should contain a recommended pesticide. Large commercial flocks can be treated for infestations most economically by dipping or spraying after shearing, and spraying again in the fall.
FAMILY-CHLOROPIDAE-CHLOROPID FLIES
These flies are too small to be recognized without the aid of a microscope. However, there are a few common species in the group that can be distinguished behaviorally. These are namely the eye gnats. The eye gnats, 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 secretions. 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.
An eye gnat commonly attracted to the eyes especially in hot weather.
FAMILY BOMBYLIDAE-BEE FLIES
This is a large family with hundreds of genera, although their life cycles are not well known. Adults generally feed on nectar and pollen, thus are pollinators of flowers. They superficially resemble bees, thus are commonly called bee flies, and this may offer the adults some protection from predators. The larval stages are predators or parasitoids of other insect eggs and larvae. The adult females usually deposit eggs in the vicinity of possible hosts, quite often in the burrows of beetles or wasps/solitary bees. Where most often in the insect world parasitoids are highly specific in the host species that they will infect, some bombyliids are opportunistic and will use a variety of hosts.
While bombyliids have a great variety of species, rarely are individuals of any one species abundant, and this is perhaps one of the poorest known families of insects relative to its size. There are at least 4,500 described species, and probably thousands as of yet undescribed.
Bee Fly.
FAMILY-OESTRIDAE-BOTS AND WARBLES
They are very large hairy flies that are commonly mistaken for bumble bees. They fly extremely fast and are rarely collected. The adults typically lack mouthparts.
The cattle grubs 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.
A 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 bomb fly. 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. (There is a hilarious account of some cows’ reaction to the bot fly’s loud buzzing in All Creatures Great and Small by James Herriot, a Yorkshire vet.)
Once hatched, the larvae bore into the skin and internally travel up the legs through the tissues, spend a time in the stomach and finally end 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 larvae eat their way through the skin and drop 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”.
Human Bot Fly-Dermatobia hominis. This 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. It 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.
An adult human bot fly. Image courtesy Marcelo de Campos Pereira, University of Sau Paolo, Brazil.
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 mosquito makes contact with a potential host, the larva can immediately emerge and is in optimum position for attachment. When the mosquito begins to feed on its host the fly larvae emerges 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.
A common fly carrying the eggs of the human bot fly. Image courtesy Marcelo Campo De Pereira of University of Sau Paulo, Brazil.
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 develop 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”.
Horse Bot Fly. Gasterophilus intestinalis. Worldwide, nine 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.
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.
Horse Bot Larvae feeding on horses’s gut. http://commons.wikimedia.org/wiki/User:Kalume
The third instar larvae are relatively large, between 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.
Damage. The horse bot fly causes indirect damage to the horse through attempts at egg laying. The dive-bombing action of the bot fly can range from a simple annoyance to severe fright among horses. Injuries may result as the horse tries to rid themselves of this hovering fly. Weight-loss may occur if the annoyance is great enough to cause the horse to stop grazing.
The direct damage the bot fly causes occurs after the larvae enter the animal's mouth and gastrointestinal tract. When the first instar larvae burrow into the mouth, the horse may experience severe irritation, as well as the development of pus pockets and loosened teeth. Loss of appetite may develop. As the second and third instar larvae inhabit the gastrointestinal tract and attach to the stomach and intestine, multiple complications may arise. Larvae present in large numbers in the stomach can cause blockages and lead to colic. Horses are capable of tolerating an infestation of 100 larvae. Large numbers of larvae impact the host by damaging the tissue of the stomach or the gut lining and consuming the needed nutrients. Other health issues that may develop due to a severe infestation of these larvae include: chronic gastritis, ulcerated stomach, esophageal paralysis, peritonitis, stomach rupture, squamous cell tumors, and anemia.
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).
Management
Feces should be cleaned and transported away since this is the area where the final development occurs before the fly emerges. Bot eggs can be removed from the horse's body by several methods. A tool with a sharp edge or a form of sand paper can be used to scrape away the bot eggs. Warm water with appropriate insecticide can be used to induce the eggs to hatch and kill the larvae. The first stage larvae die soon after hatching if they do not reach the mouth. Protection, such as rubber gloves, help in preventing larvae from entering the handler.
An insecticide can also be applied weekly during the peak egg laying season to the areas of the body covered with bot eggs. Oral medications can be used to reduce the numbers of larvae inside of the stomach. Commonly used medications include avermectins, which come in different formulations: liquids, gels, boluses, and feed additives. Avermectins work to control the adult and larval fly stages. The horse should be treated within one month after eggs are seen during the early summer months. A second treatment should be administered in the Fall to control the second and third stage larvae.
Sheep Bot Fly, Oestrus ovis. The larvae of this parasite feed on mucous surfaces of the nasal passages and sinuses of sheep and goats. It has been estimated that sheep bot fly larvae cause a 4 percent decrease in weight gain. Drummond in 1981 estimated annual losses in sheep production in the United States due to sheep bot fly to be $13.5 million. An external sign of infestation is the appearance of a slightly too moderate runny nose; this condition increases in severity as the infestation develops.
The adult sheep bot fly, which has a bee-like appearance, is approximately 3/8 to ½ inch in length. As with other bot species adults do have mouthparts and consequently don’t feed nor do females do not lay ggs directly on the host. Instead, fertile eggs hatch within the female fly, and she deposits newly hatched larvae in the nostrils of the host. Sheep react to the larva-laying attempts of the flies by running or walking with their noses close to the ground or huddling in groups.
Because the egg stage hatches within the female fly, it is not seen. They exhibit 3 larval instars. These are seldom seen because they develop exclusively within the nasal passage and sinuses of the host. The first instar, which is only a little more than 1/32 inch in length, is found on the mucosa lining of the nasal passages. As this stage moves from the nasal passages toward the openings of the sinuses, it molts to the second instar. The third instar grows within the sinuses up to ¾ inch in length until it is ready to leave the host. Fully developed larvae leave the sinuses and nasal passage, drop to the ground to pupate in the soil. The timing of the sheep bot fly life cycle is dependent upon climate. In southern areas of the United States where winters are moderate, adult flies are active during all but the very coldest months, and larvae continue to develop within the host during winter. In northern areas, adult flies are active only during the summer and early fall. In late fall and winter, first instar larvae are either in a suspended state of development or are growing slowly. In the warm days of summer, larval development time may require only 25 to 35 days. Larvae that overwinter, however, may require up to 10 months to complete their development.
There is one registered insecticide for control of the nose bot, and that is ivermectin as a 0.08% sheep drench solution. It can be applied with standard animal health drenching equipment at a dose of 3.0 ml per 26 lb. animal body weight.
FAMILY-TABANIDAE-HORSE FLIES AND DEER FLIES
The horse flies, Tabanus spp, and the deer flies, Chrysops spp., 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
. An adult horse fly. Note sickle shaped antennae and large bulging eyes of top image. Left image courtesy of Marcelo de Campos Pereira, University Sao
Paulo Brazil. Right image courtesy Herbert Pase III, Texas Forest Service.
Anthrax. This is an acute disease caused by Bacillus anthracis. It affects both humans and other animals. Most forms of the disease are lethal. There are effective vaccines against anthrax, and some forms of the disease respond well to antibiotic treatment.
Like many other members of the genus Bacillus, Bacillus anthracis can form dormant spores that are able to survive in harsh conditions for extremely long periods of time, even decades or centuries. Such spores can be found on all continents, even Antarctica.[2] When spores are inhaled, ingested, or come into contact with a skin lesion on a host they may reactivate and multiply rapidly.
Anthrax commonly infects wild and domesticated herbivorous mammals which ingest or inhale the spores while grazing. Ingestion is thought to be the most common route by which herbivores contract anthrax. Carnivores living in the same environment may become infected by consuming infected animals. Diseased animals can spread anthrax to humans, either by direct contact (e.g. inoculation of infected blood to broken skin) or consumption of diseased animals' flesh.
Anthrax spores can be produced in vitro and used as a biological weapon. Anthrax does not spread directly from one infected animal or person to another; it is spread by spores. These spores can be transported by clothing or shoes. The dead body of an animal that died of anthrax can also be a source of anthrax spores.
Amongst the serious diseases that a horse fly can transmit is the Anthrax virus. If the horse fly feeds on an Anthrax infected animal, then traces of the contaminated blood can be injected into the horse fly's next victim. Anthrax is highly contagious and its symptoms include fever, colic, and swollen neck, throat and stomach. The disease rapidly progresses to fast breathing, leading to a coma. Without immediate attention, the horse will die from this infection. Avoid coming in contact with infected animals without the proper protection.
Tularemia. This disease (also known as Pahvant Valley plague, rabbit fever, deer fly fever, Ohara's fever) is a serious infectious disease caused by the bacterium Francisella tularensis. Agram-negative, non-motile coccobacillus, the bacterium has several subspecies with varying degrees of virulence. The most important of those is F. tularensis tularensis (Type A), which is found in lagomorphs in North America and is highly virulent for humans and domestic rabbits. F. tularensis palaearctica (Type B) occurs mainly in aquatic rodents (beavers, muskrats) in North America and in hares and small rodents in northern Eurasia. It is less virulent for humans and rabbits. The primary vectors are ticks and deer flies, but the disease can also be spread through other arthropods. The disease is named after Tulare County, California.
The disease is endemic in North America, and parts of Europe and Asia. The most common mode of transmission is via arthropod vectors. Rodents, rabbits, and hares often serve as reservoir hosts, but waterborne infection accounts for 5 to 10% of all tularemia in the US. Tularemia can also be transmitted by biting flies, particularly the deer fly Chrysops discalis. Individual flies can remain infective for 14 days and ticks for over 2 years. Tularemia may also be spread by direct contact with contaminated animals or material, by ingestion of poorly cooked flesh of infected animals or contaminated water, or by inhalation. The most likely method for bioterrorist transmission is through an aerosol.
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FAMILY-SIMULIDAE-BLACK FLIES.
Black flies Simulium spp. and others, are very small insects that have blade-like mouthparts that slash and lap blood much like horse and deer flies. These day flying flies are black, thick bodied, and have a prominent "hump" on the thorax. The larvae are found in running water and are attached to rocks and vegetation via silken anchor threads. The larvae pupate in cocoons under water from which the adults eventually emerge. These flies are found in the US and Canada and have caused large amounts of damage and death to livestock and in certain areas are an extreme problem to humans. The bite of these day-flying insects is initially benign. However within hours small hard red bumps develop and the intense itching begins which can last up to a week or more. Some victims have allergic reactions. Inhalation of the fly by livestock causes death.
Some species of these flies vector several serious diseases, including African river blindness and South American Robles disease. These diseases are caused by a filarial roundworm that is found underneath the skin of the victim. Lesions form in the tissues that become quite large and full of worms. The itch from these lesions is severe and has led to suicide in some victims. The young worms can also migrate into the eyes and cause blindness. This disease is very serious with over 80,000 people suffering from blindness in Africa. Spraying of insecticides does control the black fly. Treatment includes the medication Ivermectin that interrupts the reproductive lifecycle of the parasite.
FAMILY-CERATOPOGONIDAE-PUNKIES AND NO-SEEUMS.
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 costal 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 the screens with insecticides and draining their breeding sites.
64. Most Hippoboscidae are wingless and all possess beaklike mouthparts for sucking the blood of their host.
65. The common cattle grub because of the loud and aggressive nature of their attack the cattle become terror stricken and gallop madly for water or shade. This frequently result
is considerable damage to the animal.
66. The females human bot flydoes not deposit her eggs on the primary host (*us), but seeks out and captures a mosquito, fly or other arthropod and glues her eggs on this critter.
67. Horse Bot Larvae feed on horses’s gut.
68. The bite of horse flies is painful, due to the lacerating mouthparts. The fly creates a wound and then laps up the blood.
69. Most forms of the disease are lethal. There are effective vaccines against anthrax, and some forms of the disease respond well to antibiotic treatment.