Horse-flies are biting and blood-sucking members of the family Tabanidae. They are true flies in the insect order Diptera that have only one pair of membranous wings. Horse-flies are often large but agile in flight. They prefer to fly in sun-light, 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 mouth-parts and only the females bite animals to obtain enough protein from blood to produce eggs. The mouth-parts 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. The larvae are predaceous and grow in semi-aquatic habitats.
Horse-flies can transfer blood-borne diseases from one animal to another through their feeding habit. In areas where diseases occur, they have been known to carry 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.
Horse-flies have appeared in literature since Aeschylus in Ancient Greece, driving people to madness through their persistent pursuit. Shakespeare uses the theme of the maddening gadfly in his plays King Lear and Antony and Cleopatra.
The Tabanidae are true flies and members of the insect order Diptera. 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. The wings have a basal lobe (or calypter) that covers the modified knob-like hindwings or halteres. The membranous wings are clear, uniformly shaded grey or brown or patterned in some species. The terminal segment of the antenna is pointed and is annulated, appearing to be made up of several tapering rings. There is no hair or arista arising from the antennae. The tip of the legs have two lobes on the sides (pulvilli) and a central lobe or empodium in addition to two claws that let them grip surfaces. The large compound eyes are often patterned and brightly coloured in life. 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. Some species in the subfamily Pangoniinae have a long proboscis.
The larvae are long and cylindrical with small heads and twelve body segments. They have rings of tubercles known as pseudopods round the segments, and also bands of short setae. The posterior tip of each larva has a breathing siphon and a bulbous area known as Graber's organ. The outlines of the adult insect's head and wings are visible through the pupa, which has seven moveable abdominal segments, all except the front one of which bears a band of setae. The posterior end of the pupa bears a group of spine-like tubercles.
Tabanid species range from medium-sized to very large, robust insects. Most have a body length between 5 and 25 mm (0.2 and 1.0 in), with the largest having a wingspan of 60 mm (2.4 in). 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.
Tabanids are important pollinators of some flowers, in particular, several South African and Asian species of Pangoniinae have spectacularly long proboscides adapted to the extraction of nectar from flowers with long, narrow corolla tubes, such as Lapeirousia and some Pelargonium. Both males and females engage in nectar feeding.
Distribution and habitat
Horse-flies are found world-wide, except for the polar regions, but they are absent from some islands such as Greenland, Iceland and Hawaii. The genera Tabanus, Chrysops and Haematopota all occur in temperate, subtropical and tropical locations, but Haematopota are absent from Australia and South America. Horse-flies 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).
Apart from the common name "horse-flies", broad categories of biting, blood-sucking Tabanidae are variously known as breeze flies, clegs, klegs, or clags (especially for Haematopota), gadflies (because they make cattle gad about), greenheads (Tabanus), or stouts. Members of the genus Chrysops are called deer flies. In some areas of Canada, biting Tabanids are known as bull dog flies, and in Australia some species are known as March flies, a name used in other Anglophonic countries to refer to the non-blood-sucking Bibionidae.
Evolution and taxonomy
The first record of a tabanid comes from the Late Jurassic of China, and specimens from the Cretaceous have been found in England and South Africa. In the New World, the first discoveries date from the Miocene of Florissant, Colorado. These insects are recognisable as tabanids both from their mouth-parts and their wing venation. Although the blood-sucking habit is associated with a long proboscis, a fossil insect that has elongated mouth-parts is not necessarily a blood-sucker, as it may instead have fed on nectar. The ancestral diet of Tabanomorphs was probably predatory, and from this the blood-sucking habit evolved. These early blood-suckers existed before warm-blooded mammals had evolved and likely fed on reptiles. Cold blood-sucking probably preceded warm blood-sucking, but some dinosaurs are postulated to have been warm-blooded and may have been early hosts for the horse-flies.
World-wide, about 4,500 species of Tabanidae have been described, over 1,300 of them in the genus Tabanus. Their identification is based mostly on adult morphological characters of the head, wing venation and sometimes the last abdominal segment. The genitalia are very simple and do not provide clear species differentiation as in many other insect groups. In the past, most taxonomic treatments considered the family to be composed of three subfamilies: Pangoniinae (tribes Pangoniini, Philolichini, Scionini), Chrysopsinae (tribes Bouvieromyiini, Chrysopsini, Rhinomyzini) and Tabaninae (tribes Diachlorini, Haematopotini, Tabanini). Some treatments include the subfamily Adersiinae, with the single genus Adersia, and the subfamily Scepcidinae, with the two genera Braunsiomyia and Scepsis.
- Subfamily Adersiinae
- Subfamily Chrysopsinae (deer flies or banded horse-flies)
- Subfamily Pangoniinae (long-tongued horse-flies)
- Subfamily Scepcidinae
- Subfamily Tabaninae (horse-flies)
The Tabaninae lack ocelli and have no spurs on the tips of their hind tibiae. In the Pangoniinae, ocelli are present and the antennal flagellum usually has 8 annuli (or rings). In the Chrysopsinae, the antennal flagellum has a basal plate and the flagellum has 4 annuli. Females have a shining callus on the frons (front of the head between the eyes). The Adersiinae have a divided tergite on the ninth abdominal segment, and the Scepsidinae have highly reduced mouth-parts. Members of the family Pelecorhynchidae were initially included in the Tabanidae and moved into the Rhagionidae before being elevated into a separate family. The Tabanomorpha share the blood-feeding habit as a common primitive character, although this is restricted to the female.
Diet and biting behavior
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. 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.
The mouth-parts of females are of the usual Dipteran form and 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. The blood that flows from the wound is lapped up by another mouth-part which functions as a sponge. 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 which are polarized, 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.
Attack patterns vary with species: clegs fly silently and prefers to bite humans on the wrist or bare leg; large species of Tabanus buz loudly, fly low and bite ankles, legs or backs of knees; Chrysops fly somewhat higher, bite the back of the neck, and have a high buzzing note. It has been suggested that the striped hides of zebras have evolved to reduce their attractive 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. This does not preclude the possible use of stripes for other purposes such as signaling or camouflage.
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.
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 species develop in particularly wet locations while Tabanus species 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 thirteen times over the course of up to a year or more. In temperate species, the larvae have a quiescent period during winter (diapause) while tropical species breed several times 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. A respiratory siphon at the hind end allows the larvae to obtain air when submerged in water. Larvae of nearly all species are carnivorous, often cannibalistic in captivity, and consume worms, insect larvae and arthropods, while Chrysops larvae have been reported to feed on organic matter, their mouth parts indicate a predatory habit. The larvae may be parasitized by nematodes, flies of the families Bombyliidae and Tachinidae; and Hymenoptera in the family Pteromalidae. When fully developed, the larvae move into drier soil near the surface of the ground to pupate.
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.
As disease vectors
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. Species of the genus Chrysops transmit the parasitic filarial worm Loa loa between humans, and tabanids are known to transmit anthrax among cattle and sheep, and tularemia between rabbits and humans.
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.
Controlling horse-flies is difficult. Malaise traps are most often used to capture them and these can be modified with the use of baits and attractants that include carbon dioxide or octenol. A dark shiny ball suspended below them that moves in the breeze can also attract them and forms a key part of a modified "Manitoba trap" that is used most often for trapping and sampling Tabanidae. Cattle can be treated with pour-on pyrethroids which may repel the flies, and fitting them with insecticide impregnated eartags or collars has had some success in killing the 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. 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.
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."
- International Commission on Zoological Nomenclature (1961). The Bulletin of Zoological Nomenclature. International Trust for Zoological Nomenclature. p. 55.
- Chvala, M.; Lyneborg, L.; Moucha, J. (1972). Horse Flies of Europe (Diptera, Tabanidae). Entomological Society of Copenhagen. ISBN 978-0-900-84857-5.
- Moucha, J. (1976). Horse-flies (Diptera: Tabanidae) of the World: Synoptic Catalogue. Národní muzeum – Přírodovědecké muzeum.
- Chainey, John E. (1993). "Horse-flies, deer-flies and clegs (Tabanidae)". In Lane, R.P. & R.W. Crosskey. Medical Insects and Arachnids. Springer. pp. 310–332.
- Squitier, Jason M. (1 April 2014). "Deer flies, yellow flies and horse flies". Featured Creatures. University of Florida. Retrieved 24 July 2015.
- Walker, A.R. (1994). Arthropods of Humans and Domestic Animals: A Guide to Preliminary Identification. Springer. pp. 78–79. ISBN 978-0-412-57280-7.
- Cook, Gordon Charles; Zumla, Alimuddin (2009). Manson's Tropical Diseases. Elsevier. p. 1752. ISBN 1-4160-4470-1.
- 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.
- Goldblatt, Peter; Manning, John C.; Bernhardt, Peter. "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.
- Combs, J.K.; Pauw, A. "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.
- 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.
- Webster's Revised Unabridged Dictionary (1913), p. 707.
- "Notch-horned Cleg-fly Haematopota pluvialis". The Wildlife Trusts. Retrieved 20 August 2015.
- Graves, Annie (July 2013). "Greenheads". Yankee Magazine. Retrieved 20 August 2015. Text " Learn about Greenhead Flies, the Beasts of the Northern Wild " ignored (help)
- Jamieson, John (1840). An Etymological Dictionary of the Scottish Language: Cleg. W. Tait. p. 232.
- Austen, Ernest Edward (1906). British blood-sucking flies. London: Britis Museum. p. 31.
- "What does "bulldog fly" mean". Webster's Third New International Dictionary. Retrieved 30 July 2015.
- Doggett, Stephen L. (20 January 2010). "Biting flies". University of Sydney and Westmead Hospital: Department of Medical Entomology. Retrieved 30 July 2015.
- "Family Bibionidae – March Flies". BugGuide. Retrieved 30 July 2015.
- Martins-Neto, Rafael Gioia (2003). "The fossil tabanids (Diptera Tabanidae): When they began to appreciate warm blood and when they began transmit diseases?" (PDF). Mem Inst Oswaldo Krubs 98 (1): 29–34.
- Grimaldi, David; Engel, Michael S. (2005). Evolution of the Insects. Cambridge University Press. pp. 522–. ISBN 978-1-107-26877-7.
- Mackerras, I.M., (1954). "The classification and distribution of Tabanidae (Díptera). I. General review". Australian Journal of Zoology 2: 431–454.
- "Tabanidae". Tabanidae. Retrieved 19 August 2015.
- Colless, D.H.; McAlpine, D.K. (1991). The Insects of Australia. Volume 2. (2 ed.). CSIRO. pp. 754–755. ISBN 978-0522846386.
- Mackerras, I.M. (1954). The Classification and Distribution of Tabanidae (Diptera). p. 584.
- Mackerras, I.M. (1955). "The classification and distribution of Tabanidae (Diptera). III. Subfamilies Scepsidinae and Chrysopinae". Australian Journal of Zoology 3: 583–633.
- Morita, Shelah I. (2008). "A phylogeny of long-tongued horse flies (Diptera:Tabanidae:Philoliche) with the first cladistic review of higher relationships within the family". Invertebrate Systematics 22: 311–327.
- 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.
- "Horse Flies and Deer Flies". University of Kentucky. Retrieved 24 July 2015.
- Kazimírová M.; Šulanová M.; Kozánek M.; Takáč P.; Labuda M.; Nuttall P.A. (2001). "Identification of Anticoagulant Activities in Salivary Gland Extracts of Four Horsefly Species (Diptera, Tabanidae)". Haemostasis 31: 294–305. doi:10.1159/000048076.
- Thomas, Anthony (1 April 2012). "Horse Fly head" (PDF). Micscape Magazine. Microscopy-UK. Retrieved 25 July 2015.
- "Horse and Deer Flies". Medical Entomology. Purdue University.
- Horváth G; Majer J; Horváth L; Szivák I; Kriska G. (2008). "Ventral polarization vision in tabanids: horseflies and deerflies (Diptera: Tabanidae) are attracted to horizontally polarized light". Naturwissenschaften 11: 1093–100. doi:10.1007/s00114-008-0425-5.
- Marren, Peter; Mabey, Richard (2010). Bugs Britannica. Chatto & Windus. pp. 311–312. ISBN 978-0-7011-8180-2.
- Caro, Tim; Izzo, Amanda; Reiner, Robert C. Jr; Walker, Hannah; Stankowich, Theodore (2014). "The function of zebra stripes". Nature Communications 5: 3535. doi:10.1038/ncomms4535.
- 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.
- da Rosa, Gustavo A. Braga (2006). "Predation of hilltopping horse-flies (Tabanidae) by birds in Brazil" (PDF). Ornitologia Neotropical 17: 619–622.
- 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.
- 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.
- Sullivan, Robert T. (1981). "Insect swarming and mating". Florida Entomologist 64 (1): 44–65.
- Cheng, Thomas C. (2012). General Parasitology. Elsevier Science. p. 660. ISBN 978-0-323-14010-2.
- 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.
- Quercia, O.; Emiliani, F.; Foschi, F.G.; Stefanini, G.F. "The wasp-horsefly syndrome" (PDF). European Annals of Allergy and Clinical Immunology 40 (3): 61–63.
- Williams, R. (26 July 2013). "Allergic reaction to horsefly bite kills father of four in seconds after anaphylactic shock". The Independent.
- French, Frank E.; Kline, Daniel L. (1989). "l-Octen-3-ol, an Effective Attractant for Tabanidae (Diptera)". Journal of Medical Entomology 26 (5): 459–461. doi:10.1093/jmedent/26.5.459.
- Axtell, R.C.; Edwards, T.D.; Dukes, J.C. (1975). "Rigid canopy trap for Tabanidae (Diptera)". J. Georgia Entomol. Soc. 10 (1): 64–67.
- Stagman, Myron (11 August 2010). Shakespeare’s Greek Drama Secret. Cambridge Scholars Publishing. pp. 205–208. ISBN 978-1-4438-2466-8.
- Walker, John Lewis (2002). Shakespeare and the Classical Tradition: An Annotated Bibliography, 1961–1991. Taylor & Francis. p. 363. ISBN 978-0-8240-6697-0.
- Sherborn, C.D. (1850). Index Animalum. H, I, J, K, L. p. 2889.
- Middlekauff, Woodrow Wilson; Lane, Robert S. (1980). Adult and Immature Tabanidae (Diptera) of California. University of California Press. p. 40. ISBN 978-0-520-09604-2.
Data related to Tabanidae at Wikispecies
|Look up horsefly in Wiktionary, the free dictionary.|
- Family Tabanidae at EOL
- Tabanidae in Italian
- Horsefly Tabanus sp. diagnostic photographs
- Family description and images
- Chrysops, Diachlorus, and Tabanus spp. on the UF / IFAS Featured Creatures Web site
- Diachlorus ferrugatus, yellow fly on the UF / IFAS Featured Creatures Web site
- Information about horsefly bites.