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Horse fly Tabanus 2.jpg
Hybomitra micans
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Suborder: Brachycera
Infraorder: Tabanomorpha
Superfamily: Tabanoidea
Family: Tabanidae
Latreille, 1802[1]

as listed in ITIS:
See text

Horse-fly is the most widely used English common name for biting and bloodsucking members of the family Tabanidae. These are true flies in the insect order Diptera, which use only the front wings for flight. Horse-flies are often large, but are agile in flight. 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.

Adult horse-flies feed on nectar and plant exudates; the males have weak mouthparts and only the females bite animals, to obtain enough protein from blood to produce eggs. The mouthparts of females are formed into a stout stabbing organ with two pairs of sharp cutting blades, and a spongelike part used to lap up the blood that flows from the wound.

Horse-flies are vectors for blood-borne diseases of animals and humans, such as the equine infectious anaemia virus, some trypanosomes, the filarial worm Loa loa, anthrax among cattle and sheep, and tularemia. As well as making life outdoors uncomfortable for humans, they can reduce growth rates in cattle and lower the milk output of cows if suitable shelters are not provided.

Gadflies have appeared in literature since Aeschylus in Ancient Greece, driving people to madness through pursuit and constant observation. Shakespeare uses the theme in his plays King Lear and Antony and Cleopatra.


Horse-flies Haematopota pluvialis feeding on a horse's head

The Tabanidae are true flies and members of the insect order Diptera. Tabanidae species range from medium-sized to very large insects. Some species, such as deer flies and the Australian March flies, are known for being extremely noisy during flight, though clegs, for example, fly quietly and bite with little warning. Tabanids are agile fliers; Hybomitra have been observed to perform aerial maneuvers similar to those performed by fighter jets, such as the Immelman turn.[2]

In spite of their roles as pests, Tabanidae also are important pollinators of some flowers. In particular, several South African species have spectacularly long proboscides adapted to the extraction of nectar from flowers with long, narrow corolla tubes, such as Lapeirousia[3] and some Pelargonium.[4] Tabanidae occur worldwide, being absent only on some remote oceanic islands and at extreme northern and southern latitudes.

Common names[edit]

Apart from the common name "horse-flies", broad categories of biting, bloodsucking Tabanidae are variously known as breeze flies,[5] clegs, klegs, or clags, gadflies (because they make cattle gad about), or stouts.[6][7] Members of the genus Chrysops are called deer flies. In some areas of Canada, biting Tabanids are known as bull dog flies,[8] and in Australia some species are known as March flies,[9] a name used in other English-speaking countries to refer to the non-bloodsucking Bibionidae.[10]


Worldwide about 4,500 species of Tabanidae have been described, over 1,300 of them in the genus Tabanus. Three subfamilies are widely recognised:

Two well-known genera are the common horse-flies, genus Tabanus Linnaeus, 1758 and the deer flies, genus Chrysops Meigen, 1802. Both genera give their names to subfamilies. The "Blue Tail Fly" in the eponymous song was probably the mourning horsefly (Tabanus atratus), a tabanid with a blue-black abdomen common to the southeastern United States.[11]


Head of Tabanus atratus showing large compound eyes, short antennae (between and below the eyes) and stout piercing mouthparts

Adult tabanids are large flies with prominent compound eyes, short antennae composed of three segments, and wide bodies. In females, the eyes are widely separated but in males they are almost touching. Both head and thorax are clad in short hairs. Deer flies in the genus Chrysops are up to 1 centimetre (0.39 in) long, have yellow to black bodies and striped abdomens and have membranous wings with dark patches. Horse-flies (genus Tabanus) are larger, up to 2.5 centimetres (1 in) in length and are mostly dark brown or black, with dark eyes, often with a metallic sheen. Yellow flies (genus Diachlorus) are similar in shape to deer flies but have yellowish bodies and the eyes are purplish-black with a green sheen.[12]

Distribution and habitat[edit]

Horse-flies and deer flies are found worldwide, except for the polar regions, but they are absent from some islands such as Greenland, Iceland and Hawaii.[12] They mostly occur in warm areas with suitable moist locations for breeding, but also occupy a wide range of habitats from deserts to Alpine meadows. They are found from sea level to at least 3,300 metres (10,800 ft).[13]


Diet and biting behavior[edit]

Haematopota pseudolusitanica female showing the stout cutting mouthparts

Adult horse flies feed on nectar and plant exudates. In addition to this, females of most species are anautogenous, meaning they require a blood meal before they are able to reproduce effectively. The females of many tabanid flies bite animals, including humans, to feed on their blood. It seems that they are attracted to a potential victim by its movement, its warmth, its surface texture and the carbon dioxide it breathes out.[14] 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. Because their bite is irritating to the victim, they are often brushed off, and may have to visit multiple hosts in order to obtain sufficient blood. This behaviour means that they may carry disease-causing organisms from one host to another.[13]

Tabanus mouthparts: the sharp cutting stylets are on the right, the spongelike lapping part in the centre.

The mouthparts of females consist of a bundle of six chitinous stylets that, together with a fold of the fleshy labium, form the proboscis. On either side of these are two maxillary palps. When the insect lands on an animal it grips the surface with its clawed feet, the labium is retracted, the head is thrust downwards and the stylets slice into the flesh. Some of these have sawing edges and muscles can move them from side-to-side to enlarge the wound. Saliva containing anticoagulant is injected into the wound to prevent clotting.[14][15] The blood that flows from the wound is lapped up by another mouthpart which functions as a sponge.[16] Horse-fly bites can be painful for a day or more; fly saliva may provoke allergic reactions such as hives and difficulty with breathing. Tabanid bites can make life outdoors unpleasant for humans, and can reduce milk output in cattle. They are attracted by reflections from water, making them a particular nuisance near swimming pools. Since tabanids prefer to be in sunshine, they normally avoid shaded places such as barns, and are inactive at night.[14]

Attack patterns vary with species: the cleg flies silently and prefers to bite humans on the wrist or bare leg; large species of Tabanus fly in low and bite ankles, legs or backs of knees, buzzing loudly; Chrysops flies somewhat higher, bites the back of the neck, and has a high buzzing note.[17] The striped hides of zebras are less attractive to horse-flies than either plain dark or plain white hides, so it is possible that zebras evolved stripes partly to avoid horse-fly bites. This does not preclude the possible use of stripes for other purposes such as signaling or camouflage.[18]


The horse guard wasp, Stictia carolina, catches horse-flies to provision its nest.

Aside from generalized predators such as birds, specialist predators, such as the horse guard wasp, a bembicinid wasp also preferentially attack horse flies, catching them to provision their nests.[19]


Mating is done in swarms, generally at landmarks such as hilltops. The season and time of day, and type of landmark, used for mating swarms is specific to particular species.[20]

Eggs are laid on stones or vegetation near water, in clusters of up to one thousand, especially on emergent water plants. The eggs are white at first but darken with age. They hatch after about six days, the emerging larvae using a special hatching spike to open the egg case. The larvae fall into the water or onto the moist ground below. Chrysops spp. develop in particularly wet locations while Tabanus spp. prefer drier places. The larvae are legless grubs, tapering at both ends. They have small heads and eleven or twelve segments, and moult six to nine times over the course of up to a year. In the majority of species they are white, but in some they are greenish or brownish, and they often have dark bands on each segment. Tabanus larvae are carnivorous and consume worms, insect larvae and arthropods, while Chrysops larvae feed on organic matter. When fully developed, the larvae move into drier soil near the surface of the ground to pupate.[12]

The pupae are brown and glossy, rounded at the head end and tapering at the other end. Wing and limb buds can be seen and each abdominal segment is fringed with short spines. After about two weeks, metamorphosis is complete, the pupal case splits along the thorax and the adult fly emerges. Males usually appear first, but when both sexes have emerged, mating takes place, courtship starting in the air and finishing on the ground. The female needs to feed on blood before depositing her egg mass.[12]

As disease vectors[edit]

A bite of horse-fly on a human.

Tabanids are known vectors for some blood-borne bacterial, viral, protozoan and worm diseases of mammals, such as the equine infectious anaemia virus and various species of Trypanosoma which cause diseases in animals and humans.[21] Species of the genus Chrysops transmit the parasitic filarial worm Loa loa between humans,[22] and tabanids are known to transmit anthrax among cattle and sheep, and tularemia between rabbits and humans.[21]

Blood loss is a common problem in some animals when large flies are abundant. Some animals have been known to lose up to 300 millilitres (11 imp fl oz; 10 US fl oz) of blood in a single day to tabanid flies, a loss which can weaken or even kill them. There are anecdotal reports of horse-fly bites leading to fatal anaphylaxis in humans, an extremely rare occurrence.[23]

In literature[edit]

Thomas Muffett described the horse-fly in his 1634 book Theatre of Insects.

The Ancient Greek playwright Aeschylus has a gadfly pursue and torment Io, a maiden associated with the moon, watched constantly by the eyes of the herdsman Argus, associated with all the stars: "Io: Ah! Hah! Again the prick, the stab of gadfly-sting! O earth, earth, hide, the hollow shape—Argus—that evil thing—the hundred-eyed." William Shakespeare, inspired by Aeschylus, has Tom o'Bedlam in King Lear, "Whom the foul fiend hath led through fire and through flame, through ford and whirlpool, o'er bog and quagmire", driven mad by the constant pursuit.[24] In Antony and Cleopatra, Shakespeare likens Cleopatra's hasty departure from the Actium battlefield to that of a cow chased by a gadfly: "The breeze [gadfly] upon her, like a cow in June / hoists sail and flies", where "June" may allude not only to the month but also to the goddess Juno who torments Io; and the cow in turn may allude to Io, who is changed into a cow in Ovid's Metamorphoses.[25]

The physician and naturalist Thomas Muffett wrote that the horse-fly "carries before him a very hard, stiff, and well-compacted sting, with which he strikes through the Oxe his hide; he is in fashion like a great Fly, and forces the beasts for fear of him only to stand up to the belly in water, or else to betake themselves to wood sides, cool shades, and places where the wind blowes through."[17]

Johann Wilhelm Meigen's Europäischen Zweiflügeligen 1790, Plate CXCIV. Nos 7, 8 and 9 are Haematopota horse-flies, H. crassicornis, H. grandis and H. pluvialis respectively.

Johann Wilhelm Meigen was a pioneering naturalist and author of Die Fliegen (Flies); he gave the name Haematopota, blood-drinker,[26] to a genus of horse-fly in 1803.[27]


See also[edit]



  1. ^ "Tabanidae". GBIF. Retrieved 2015-07-25. 
  2. ^ Wilkerson, R.C., J.F. Butler. 1984. The Immelman turn, a pursuit maneuver used by hovering male Hybomitra hinei wrighti (Diptera: Tabanidae). Annals of the Entomological Society of America 77: 293-295.
  3. ^ Goldblatt, Peter, John C. Manning, and Peter Bernhardt. "Pollination biology of Lapeirousia subgenus Lapeirousia (Iridaceae) in southern Africa; floral divergence and adaptation for long-tongued fly pollination." Annals of the Missouri Botanical Garden (1995): 517-534.
  4. ^ Combs, J. K., and A. Pauw. "Preliminary evidence that the long-proboscid fly, Philoliche gulosa, pollinates Disa karooica and its proposed Batesian model Pelargonium stipulaceum." South African Journal of Botany 75.4 (2009): 757-761.
  5. ^ Webster's Revised Unabridged Dictionary (1913), p. 707.
  6. ^ Jamieson, John (1840). An Etymological Dictionary of the Scottish Language: Cleg. W. Tait. p. 232. 
  7. ^ "Tabanidae family, horse flies, stouts, gad flies, and clegs". Insect ebook. Retrieved 30 July 2015. 
  8. ^ "What does "bulldog fly" mean". Webster's Third New International Dictionary. Retrieved 30 July 2015. 
  9. ^ Doggett, Stephen L. (20 January 2010). "Biting flies". University of Sydney and Westmead Hospital: Department of Medical Entomology. Retrieved 30 July 2015. 
  10. ^ "Family Bibionidae - March Flies". BugGuide. Retrieved 30 July 2015. 
  11. ^ Eaton, Eric R.; Kaufman, Kenn (2007). "Deer flies and horse flies". Kaufman Field Guide to Insects of North America. Hillstar Editions. p. 284. ISBN 0-618-15310-1. 
  12. ^ a b c d Squitier, Jason M. (1 April 2014). "Deer flies, yellow flies and horse flies". Featured Creatures. University of Florida. Retrieved 24 July 2015. 
  13. ^ a b Middlekauff, Woodrow Wilson; Lane, Robert S. (1980). Adult and Immature Tabanidae (Diptera) of California. University of California Press. pp. 1–2. ISBN 978-0-520-09604-2. 
  14. ^ a b c "Horse Flies and Deer Flies". University of Kentucky. Retrieved 24 July 2015. 
  15. ^ Thomas, Anthony (1 April 2012). "Horse Fly head" (PDF). Micscape Magazine. Microscopy-UK. Retrieved 25 July 2015. 
  16. ^ "Horse and Deer Flies". Medical Entomology. Purdue University. 
  17. ^ a b Marren, Peter; Mabey, Richard (2010). Bugs Britannica. Chatto & Windus. pp. 311–312. ISBN 978-0-7011-8180-2. 
  18. ^ Egri, A.; Blaho, M.; Kriska, G.; Farkas, R.; Gyurkovszky, M.; Akesson, S.; Horvath, G. (2012). "Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: An advantage of zebra stripes". Journal of Experimental Biology 215 (5): 736. doi:10.1242/jeb.065540.  edit
  19. ^ Martin, Anthony J. (2013). Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals. Indiana University Press. pp. 209–210. ISBN 0-253-00602-3. 
  20. ^ Wilkerson, R.C.; Butler, J.F.; Pechuman, L.L. (1985). "Swarming, hovering and mating behavior of male horse flies and deer flies (Diptera: Tabanidae)". Myia 3: 515–546. 
  21. ^ a b Cheng, Thomas C. (2012). General Parasitology. Elsevier Science. p. 660. ISBN 978-0-323-14010-2. 
  22. ^ Padgett, J.J.; Jacobsen, K.H. (2008). "Loiasis: African eye worm". Transactions of the Royal Society of Tropical Medicine and Hygiene 102 (10): 983–9. doi:10.1016/j.trstmh.2008.03.022. PMID 18466939. 
  23. ^ Williams, R. (26 July 2013). "Allergic reaction to horsefly bite kills father of four in seconds after anaphylactic shock". The Independent. 
  24. ^ Stagman, Myron (11 August 2010). Shakespeare’s Greek Drama Secret. Cambridge Scholars Publishing. pp. 205–208. ISBN 978-1-4438-2466-8. 
  25. ^ Walker, John Lewis (2002). Shakespeare and the Classical Tradition: An Annotated Bibliography, 1961-1991. Taylor & Francis. p. 363. ISBN 978-0-8240-6697-0. 
  26. ^ Agassiz, Louis; Corti, Elio. "Nomenclator Zoologicus". Retrieved 24 July 2015. 
  27. ^ "Haematopota Meigen, 1803". GBIF. Retrieved 24 July 2015. 

External links[edit]

Data related to Tabanidae at Wikispecies