Instruct: Given a question, retrieve relevant passages that can help answer the question.
Query: Do horse flies bite humans?
Horse-flies or horseflies (for other names, see common names) are true flies in the family Tabanidae in the insect order Diptera. They are often large and agile in flight, and the females bite animals, including humans, to obtain blood. They prefer to fly in sunlight, avoiding dark and shady areas, and are inactive at night. They are found all over the world except for some islands and the polar regions (Hawaii, Greenland, Iceland). Both horse-flies and botflies (Oestridae) are sometimes referred to as gadflies.[3]
Maturing larvae and adults of the "eye worm" occupy the subcutaneous layer of the skin – the fat layer – of humans, causing disease. The "L. loa" adult worm which travels under the skin can survive up to 10–15 years, causing inflammations known as Calabar swellings. The adult worm travels under the skin, where the female deposits the microfilariae which can develop in the host’s blood within 5 to 6 months and can survive up to 17 years. The young larvae, or microfilariae, develop in horseflies of the genus "Chrysops" (deer flies, yellow flies), including the species "C. dimidiata" and "C. silacea", which infect humans by biting them. After bites from these infected flies, the microfilariae are unique in that they travel in the peripheral blood during the day and migrate into the lungs at night.
The females of these flies are bloodsuckers, feeding on mammalian blood, mainly cattle and horses, but they can also bite humans. The males feed on nectar, especially on "Angelica sylvestris". The activity of these horseflies takes place in plain daylight, preferably in hot and muggy days and in the absence of wind. They are particularly aggressive during the full and late summer and bites cause painful welts.
Both males and females engage in nectar feeding, but in addition to this, females of most species are anautogenous, meaning they require a blood meal before they are able to reproduce effectively. To obtain the blood, the females, but not the males, bite animals, including humans. The female needs about six days to fully digest her blood meal and after that, she needs to find another host.[4] The flies seem to be attracted to a potential victim by its movement, warmth, and surface texture, and by the carbon dioxide it breathes out.[30] The flies mainly choose large mammals such as cattle, horses, camels, and deer, but few are species-specific. They have also been observed feeding on smaller mammals, birds, lizards, and turtles, and even on animals that have recently died. Unlike many biting insects such as mosquitoes, whose biting mechanism and saliva allow a bite not noticed by the host at the time, horse-fly bites are immediately irritating to the victim, so that they are often brushed off, and may have to visit multiple hosts to obtain sufficient blood. This behaviour means that they may carry disease-causing organisms from one host to another.[14] The large animals and livestock mostly bitten by horse-flies are generally powerless to dislodge the fly, so there is no selective advantage for the flies to evolve a less immediately painful bite.[31]
The pathophysiology of a spider bite is due to the effect of its venom. A spider envenomation occurs whenever a spider injects venom into the skin. Not all spider bites inject venom – a dry bite, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. The mechanical injury from a spider bite is not a serious concern for humans. Some spider bites do leave a large enough wound that infection may be a concern. However, it is generally the toxicity of spider venom that poses the most risk to human beings; several spiders are known to have venom that can cause injury to humans in the amounts that a spider will typically inject when biting.
Bites from tsetse flies are painful but these flies are not generally associated with direct causes of lost production in cattle. "Glossina morsitans" and "G.pallidipes" tsetse-flies are transmitters of various species of "Trypanosoma" protozoa causing animal trypanosomiasis (= nagana) in cattle, and other forms of trypanosomiasis in sheep, goats, pigs, camels and horses. Tsetse-flies are also notorious as transmitters of the "Trypanosoma" species causing African trypanosomiasis (= sleeping sickness) in humans.
A primary concern of the bite of a spider is the effect of its venom. A spider envenomation occurs whenever a spider injects venom into the skin. Not all spider bites involve injection of venom, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. The mechanical injury from a spider bite is not a serious concern for humans. However, it is generally the toxicity of spider venom that poses the most risk to human beings; several spiders are known to have venom that can cause injury to humans in the amounts that a spider could inject when biting.
While venoms are by definition toxic substances, most spiders do not have venom that is directly toxic (in the quantities delivered) to require medical attention and, of those that do, severity is typically mild.
Blood loss is a common problem in some animals when large flies are abundant. Some animals have been known to lose up to 300ml (11impfloz; 10USfloz) of blood in a single day to tabanid flies, a loss which can weaken or even kill them. Anecdotal reports of horse-fly bites leading to fatal anaphylaxis in humans have been made, an extremely rare occurrence.[46][47]
Bites of tabanid flies are painful. Dense populations of these flies cause severe biting stress to livestock and horses leading to reduction of gain in liveweight. These hosts may additionally suffer loss of grazing time by clustering in tight defensive packs, a situation known as fly-syndrome. Many genera of tabanid flies transmit the protozoan "Trypanosoma evansi" that causes in camels and horses the disease called surra. These flies also transmit the protozoan "T.vivax" that causes in cattle the disease called nagana. Tabanid flies are also transmitters the bacteria "Anaplasma marginale" and "A.centrale" to cattle, sheep and goats, causing anaplasmosis.
Attack patterns vary with species; clegs fly silently and prefer to bite humans on the wrist or bare leg; large species of Tabanus buzz loudly, fly low, and bite ankles, legs, or backs of knees; Chrysops flies somewhat higher, bites the back of the neck, and has a high buzzing note.[36] The striped hides of zebras may have evolved to reduce their attractiveness to horse-flies and tsetse flies than either plain dark or plain white hides. The closer together the stripes, the fewer flies are visually attracted; the zebra's legs have particularly fine striping, and this is the shaded part of the body that is most likely to be bitten in other, unstriped equids.[37] This does not preclude the possible use of stripes for other purposes such as signaling or camouflage.[38]
The flower-feeding march fly, Scaptia auriflua, is a species of horse flies that occurs in Australia. Unlike other march flies this species does not bite and does not feed on blood, it strictly drinks nectar.
The entire life cycle of the fly takes about three weeks. In addition to the bite of the tsetse fly, the disease can be transmitted by:
Horse-flies (Tabanidae) and stable flies (Muscidae) possibly play a role in transmission of nagana (the animal form of sleeping sickness) and the human disease form.
These flies are not known to transmit any disease of humans, pets or livestock, but a closely related fly transmits a virus that causes blue tongue disease of sheep. Even though they do not transmit any diseases their bites are sufficiently annoying to keep people indoors in some areas of California during much of May. They are small enough to crawl under loose clothing without being noticed. Standard mosquito repellents do not appear to be particularly effective on them.
A female wasp of this species may take anywhere from 30 to 60 flies as food to provision each one of her nests; she makes a new nest for every egg she lays. Nests are simple burrows some 15 cm deep, with a single enlarged chamber at the bottom. An egg is laid in the empty chamber, and the female wasp brings back paralyzed flies and sometimes silver-spotted skipper larvae until the chamber is full (mass provisioning), at which point she closes the nest and begins another. Numerous females often excavate nests within a small area where the soil is suitable, creating large and sometimes very dense nesting aggregations. Nearly all the prey are biting female horse-flies; exceptionally, other flies such as "Odontomyia" and the screw-worm fly "Cochliomyia" are taken.
Apart from the common name "horse-flies", broad categories of biting, bloodsucking Tabanidae are known by a large number of common names. The word "Tabanus" was first recorded by Pliny the Younger and has survived as the generic name. In general, country-folk did not distinguish between the various biting insects that irritated their cattle and called them all "gad-flies", from the word "gad" meaning a spike. The most common name is "cleg[g]", "gleg" or "clag", which comes from Old Norse and may have originated from the Vikings.[4] Other names such as "stouts" refer to the wide bodies of the insects and "dun-flies" to their sombre colouring. Chrysops species are known as "deer-flies", perhaps because of their abundance on moorland where deer roam,[4] and "buffalo-flies", "moose-flies" and "elephant-flies" emanate from other parts of the world where these animals are found.[5] In North America they are known as "breeze-flies",[6] and in Australia some are known as "March flies",[7] a name used in other Anglophonic countries to refer to the non-bloodsucking Bibionidae.[8]
While distribution is worldwide, "T. verrucosum" and other zoophilic dermatophytes are the most frequently isolated fungi from skin lesions in Southern Europe and the Middle East ("T. rubrum", a dermatophyte that more commonly infects humans, is the most prevalent in other regions). Infection to humans is largely zoonotic, and can be transmitted through direct contact or bites, but there have also been recorded cases of laboratory acquired infection, and needlestick injury during vaccination. Contact with horse blankets and cattle posts can also cause infection, and "T. verrucosum" has also been isolated from flies, although it is unknown whether flies can serve as vectors of transmission. The majority of infections are occupational, and this includes agricultural workers, veterinarians, stockyard workers, and grain handlers (infection can also be transmitted human-to-human, thus family members of these workers are also at risk). Infection of the hair is ectothrix, and can cause tinea capitis (with potential for kerions and irreversible scarring and alopecia), as well as tinea corporis, tinea manuum, tinea barbae, and tinea profunda. It is the most common cause of tinea barbae in man. A vaccine exists for both cattle and humans, and combined with hygienic practices has led to a decline in cases. It has also been observed that recurrent infections do not occur. Treatment can include oral terbinafine, fluconazole, or griseofulvin; topical treatment is also possible, however it requires more time and may have lower rates of compliance, proving to be less effective.
Horses can interpret the body language of other creatures, including humans, whom they could view as predators or providers of food, perhaps following them to see if food is near. If socialized to human contact, horses usually respond to humans as a non-threatening predator or provider. Humans do not always understand this, however, and may behave in a way, particularly if using aggressive discipline, that resembles an attacking predator and triggers the horse's fight-or-flight response. For example a person swatting high at flies might seem to be attacking the horse. On the other hand, some humans exhibit fear of a horse, and a horse may interpret this behavior as human submission to the authority of the horse, placing the human in a subordinate role in the horse's mind. This may lead the horse to behave in a more dominant and aggressive fashion. Human handlers are more successful if they learn to properly interpret a horse's body language and temper their own responses accordingly. Some methods of horse training explicitly instruct horse handlers to behave in ways that the horse will interpret as the behavior of a trusted leader in a herd and thus more willingly comply with commands from a human handler. Other methods encourage operant conditioning to teach the horse to respond in a desired way to human body language, but also teach handlers to recognize the meaning of horse body language.
Horses are not particularly vocal, but do have four basic vocalizations: the neigh or whinny, the nicker, the squeal and the snort. They may also make sighing, grunting or groaning noises at times.
The University of Georgia claims that there exists a biting kind of gnat, which is a black fly (buffalo gnat). The scientists compare the painful and vicious bite of the black fly with the fire ant bite. Meanwhile, the North Carolina State University entomologists explain that a widely spread type of biting flies, called biting midges, also belongs to the gnat species: "Biting midges ("Culicoides" sp.) are small, sometimes barely visible, blood-sucking flies more commonly known in many areas as biting gnats, sand flies, biting midges, punkies or "no-see-ums".
Severe biting stress to cattle, sheep and horses is caused. Horses suffer from a cutaneous hypersensitivity reaction called sweet-itch, or Queensland-itch that is caused by antigenic components of saliva of biting midges. Poultry may be severely afflicted with biting stress. Species such as "Culicoides imicola" and "Culicoides variipennis" transmit bluetongue virus between sheep and cattle (see diagram and photograph above), and they transmit African horse sickness virus between horses and other equids. "Culicoides" midges transmit "Leucocytozoon" protozoa to poultry birds.
University of Kentucky entomologists consider only non-biting flies to be gnats, and the Institute of Agriculture and Natural Resources of the University of Nebraska–Lincoln classifies fungus gnats and other non-biting flies as gnats. Certain universities also distinguish eye gnats: the Smithsonian Institution describes them as "non-biting flies, no bigger than a few grains of salt, ... attracted to fluids secreted by your eyes".
Dipterans are an important group of insects and have a considerable impact on the environment. Some leaf-miner flies (Agromyzidae), fruit flies (Tephritidae and Drosophilidae) and gall midges (Cecidomyiidae) are pests of agricultural crops; others such as tsetse flies, screwworm and botflies (Oestridae) attack livestock, causing wounds, spreading disease, and creating significant economic harm. See article: Parasitic flies of domestic animals. A few can even cause myiasis in humans. Still others such as mosquitoes (Culicidae), blackflies (Simuliidae) and drain flies (Psychodidae) impact human health, acting as vectors of major tropical diseases.
Among these, "Anopheles" mosquitoes transmit malaria, filariasis, and arboviruses; "Aedes aegypti" mosquitoes carry dengue fever and the Zika virus; blackflies carry river blindness; sand flies carry leishmaniasis.
Other dipterans are a nuisance to humans, especially when present in large numbers; these include houseflies, which contaminate food and spread food-borne illnesses; the biting midges and sandflies (Ceratopogonidae) and the houseflies and stable flies (Muscidae). In tropical regions, eye flies (Chloropidae) which visit the eye in search of fluids can be a nuisance in some seasons.
Although "Chrysops silacea" and "C. dimidiata" are attracted to canopied rainforests, they do not do their biting there. Instead, they leave the forest and take most blood meals in open areas. The flies are attracted to smoke from wood fires and they use visual cues and sensation of carbon dioxide plumes to find their preferred host, humans.
The "Hybomitra aterrima var. auripila" (Meigen) has the abdominal tergites more or less distinctly golden-yellow pubescent on posterior margins.
Males of these horse flies feed on plant juices, while female are bloodsuckers, feeding mainly on mammalian blood, as they require a blood meal before they are able to reproduce. They may be very annoying for cattle, but usually they do not bite people.
Tabanus bovinus, sometimes called the pale giant horse-fly, is a species of biting horse-fly. As the name suggests, it prefers bovine animals as the source of blood, although it may bite other kind of mammals as well. The insect is relatively large for a horse-fly, adults usually being 25–30 mm long. Like most other horseflies, its compound eyes are very colorful with stripe-like patterns. Its body and wings are mostly colored brownish gray. It is quite fast and an able flier, being capable of evading most attempts to swat it with ease. It bites humans infrequently, because of its preference of bovine animals. This loud-buzzing horse-fly can be a nuisance, as it circles around its target and occasionally lands to deliver a bite (in the case of humans, the fly usually takes off again instead). However, to humans it is considerably less harmful than deer flies ("Chrysops"), which bite much more vigorously.
While the term "shark attack" is in common use for instances of humans being wounded by sharks, it has been suggested that this is based largely on the misconception that white sharks and other large predatory sharks (such as bull and tiger sharks) seek out humans as prey. A recent review recommends that only in the very rare instances where a shark clearly predated on a human should the bite incident be termed an "attack," which implies predation, and that otherwise it is more accurate to class bite incidents as "sighting", "encounter", "bite incident", or "fatal bite incident". Sightings do not include physical interaction, encounters include physical interaction without harm, shark bites include minor and major shark bite incidents, including those that do and do not require medical attention, and fatal shark bite incidents are those that result in death. The study suggests that only in a case where an expert validates the predatory intent of a shark would it be appropriate to term a bite incident an attack.[111]