Tabanidae
Horse flies and deer flies are true flies in the family Tabanidae in the insect order Diptera. The adults are often large and agile in flight. Females parasitize land vertebrates, including humans, biting them 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. Both horse flies and botflies are sometimes referred to as gadflies. Contrary to popular belief, horse flies can not see infrared light or otherwise detect heat at a distance.
Adult horse flies feed on nectar and plant exudates; males have weak mouthparts, but females have mouthparts strong enough to puncture the skin of large animals. This is for the purpose of obtaining 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. The larvae are predaceous and grow in semiaquatic habitats.
Female horse flies can transfer blood-borne diseases from one animal to another through their feeding habit. In areas where those 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. They can reduce growth rates in cattle and lower the milk output of cows if suitable shelters are not provided.
Horse flies have long appeared in literature. The father of Greek tragedy, Aeschylus, depicts a gadfly driving Io to madness in Prometheus Bound through its relentless pursuit. The philosopher Socrates later adopted the gadfly as an ironic mascot for his persistent questioning of those who spoke with him.
Common names
Tabanidae are known by a large number of common names. The subfamily Chrysopsinae is known as deer flies, perhaps because of their abundance on moorland where deer roam, and buffalo-flies, moose-flies and elephant-flies emanate from other parts of the world where these animals are found. The term "horse-fly" refers primarily to Tabaninae that are typically larger and stouter, and that lack the banded wings deer flies have. Other common names include tabanids, gadflies, green-headed flies, and green flies.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 "spike". Other common names include "cleg", "gleg" or "clag", which come from Old Norse and may have originated from the Vikings. Other names such as "stouts" refer to the wide bodies of the insects and "dun-flies" to their sombre colouring. In Australia and the UK they are also known as March flies, a name used in other Anglophonic countries to refer to the non-bloodsucking Bibionidae.
Description
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; in males, however, they are almost touching. The eyes are often patterned and brightly coloured in living tabanids but appear dull in preserved specimens. The terminal segment of the antennae is pointed and annulated, appearing to be composed of several tapering rings. There are no hairs or arista stemming from the antennae. Both the head and thorax are clad in short hairs, but no bristles are on the body. The membranous forewings are clear, either shaded uniformly grey or brown, or patterned in some species; they have a basal lobe that covers the modified knob-like hindwings or halteres. The tips of the legs have two lobes on the sides and a central lobe in addition to two claws that enable them to grip to surfaces. Species recognition is based on details of head structures, wing venation, and body patterning; minute variations of surface structure cause subtle alterations of the overlying hairs, which alters the appearance of the body.File:ITWAMOL - Fig 169.png|thumb|right|Diagram of the head of Tabanus atratus. Large compound eyes, short antennae, blade-like mandible |alt=Diagram of the facial features of Tabanus atratus
Tabanid species range from medium-sized to very large, robust insects. Most have a body length between, with the largest having a wingspan of. Deer flies in the genus Chrysops are up to long, have yellow to black bodies and striped abdomens, and membranous wings with dark patches. Horse-flies are larger, up to in length and are mostly dark brown or black, with dark eyes, often with a metallic sheen. Yellow flies 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 an exceptionally long proboscis.
Vision
Like in many insects, the compound eyes of tabanids are capable of detecting the polarization of light, And in female tabanids, it's a determining factor in their host targeting. The optical units making up the compound eye of flies of the suborder brachycera contain a cluster of 8 photoreceptor cells ; R1–6 on the cluster's rim are for achromatic vision and motion detection, while R7 and R8 in the cluster's center detect color and polarity of incoming light. Despite the clear differences between the outer R1-6 and the inner R7 and R8, the two groups do overlap to an extent in their function. There are two kinds of ommatidia, termed pale and yellow, that differ only in the wavelength sensitivity of R8. R1–R6 share a sensitivity to light from ultraviolet into the green wavelength range. The sensitivity of R7 peaks in ultraviolet, while R8 peaks in blue and green for pale and yellow respectively. With the peak sensitivity of the color-seeing retinula cells being in the blue and green wavelength ranges, they are not able to detect significant amounts of light in the infrared and red wavelengths. They are therefore not able to see the heat of objects by the infrared light they radiate.Larva
The larvae are long and cylindrical or spindle-shaped with small heads and 12 body segments. They have rings of tubercles known as pseudopods around 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.Distribution and habitat
Tabanids are found worldwide, 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 is absent from Australia and South America. 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.Evolution and taxonomy
The oldest records of the family come from the Early Cretaceous, with the oldest record being Eotabanoid, known from wings found in the Berriasian Purbeck Group of England. Although the bloodsucking habit is associated with a long proboscis, a fossil insect that has elongated mouthparts is not necessarily a bloodsucker, as it may instead have fed on nectar. The ancestral tabanids may have co-evolved with the angiosperm plants on which they fed. With a necessity for high-protein food for egg production, the diet of early tabanomorphs was probably predatory, and from this, the bloodsucking habit may have evolved. In the Santana Formation in Brazil, no mammals have been found, so the fossil tabanids found there likely fed on reptiles. Cold bloodsucking probably preceded warm bloodsucking, but some dinosaurs are postulated to have been warm-blooded and may have been early hosts for the horse-flies.The Tabanidae are true flies and members of the insect order Diptera. With the families Athericidae, Pelecorhynchidae and Oreoleptidae, Tabanidae are classified in the superfamily Tabanoidea. Along with the Rhagionoidea, this superfamily makes up the infraorder Tabanomorpha. Tabanoid families seem to be united by the presence of a venom canal in the mandible of the larvae. Worldwide, about 4,455 species of Tabanidae have been described, over 1,300 of them in the genus Tabanus.
Tabanid 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, Chrysopsinae, and Tabaninae. Some treatments increased this to five subfamilies, adding the subfamily Adersiinae, with the single genus Adersia, and the subfamily Scepcidinae, with the two genera Braunsiomyia and Scepsis.A 2015 study by Morita et al. using nucleotide data, aimed to clarify the phylogeny of the Tabanidae and supports three subfamilies. The subfamilies Pangoniinae and Tabaninae were shown to be monophyletic. The tribes Philolichini, Chrysopsini, Rhinomyzini, and Haematopotini were found to be monophyletic, with the Scionini also being monophyletic apart from the difficult-to-place genus Goniops. Adersia was recovered within the Pangoniini as were the genera previously placed in the Scepcidinae, and Mycteromyia and Goniops were recovered within the Chrysopsini.
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 eight annuli. In the Chrysopsinae, the antennal flagellum has a basal plate and the flagellum has four annuli. Females have a shining callus on the frons. The Adersiinae have a divided tergite on the ninth abdominal segment, and the Scepsidinae have highly reduced mouthparts. Members of the family Pelecorhynchidae were initially included in the Tabanidae and moved into the Rhagionidae before being elevated into a separate family. The infraorder Tabanomorpha shares the blood-feeding habit as a common primitive characteristic, although this is restricted to the female.
Two well-known genera are the common horse-flies, Tabanus, named by Swedish taxonomist Carl Linnaeus in 1758, and the deer flies, Chrysops, named by the German entomologist Johann Wilhelm Meigen in 1802. Meigen did pioneering research on flies and was the author of Die Fliegen ; he gave the name Haematopota, meaning "blood-drinker", to another common genus of horse-flies.