Horse-fly

Horse-flies or horseflies are true flies in the family Tabanidae in the insect order Diptera. They are often large and agile in flight, and only the female horseflies 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.

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. 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 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 appeared in literature since Aeschylus in Ancient Greece mentioned them driving people to "madness" through their persistent pursuit.

Common names

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 , "gleg" or "clag", which comes 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. ''Chrysops'' species are 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. In North America they are known as "horse flies" or "breeze-flies", and in Australia and the UK they are 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 but in males, they are almost touching; they are often patterned and brightly coloured in life but appear dull in preserved specimens. The terminal segment of the antennae is pointed and is annulated, appearing to be made up of several tapering rings. There are no hairs or arista arising from the antennae. Both head and thorax are clad in short hairs, but no bristles are on the body. The membranous forewings are clear, uniformly shaded grey or brown, or patterned in some species; they have a basal lobe (or calypter) that covers the modified knob-like hindwings or halteres. The tips of the legs have two lobes on the sides (pulvilli) and a central lobe or empodium in addition to two claws that enable them to grip surfaces. Species recognition is based on details of head structures (antennae, frons, and maxillae), the wing venation and the body patterning; minute variations of surface structure cause subtle alterations of the overlying hairs which alters the appearance of the body.

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 (genus '' Tabanus'') are larger, up to 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 an exceptionally long proboscis (tubular mouthpart).

The larvae are long and cylindrical or spindle-shaped with small heads and 12 body segments. They have rings of tubercles (warty outgrowths) known as pseudopods around the segments, and also bands of short setae (bristles). 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.

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'' species have been observed to perform aerial manoeuvres similar to those performed by fighter jets, such as the Immelmann turn. Horseflies can lay claim to being the fastest flying insects; the male ''Hybomitra hinei wrighti'' has been recorded reaching speeds of up to when pursuing a female.

Distribution and habitat

Horse-flies 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. 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 .

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 (145-140 million years ago) 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 (tribes Pangoniini, Philolichini, Scionini), Chrysopsinae (tribes Bouvieromyiini, Chrysopsini, Rhinomyzini), and Tabaninae (tribes Diachlorini, Haematopotini, Tabanini). 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.

*Subfamily Chrysopsinae (deer flies or banded horse-flies)
*Subfamily Pangoniinae (long-tongued horse-flies)
*Subfamily Tabaninae (horse-flies)

The Tabaninae lack ocelli (simple eyes) and have no spurs on the tips of their hind tibiae. In the Pangoniinae, ocelli are present and the antennal flagellum (whip-like structure) usually has eight annuli (or rings). In the Chrysopsinae, the antennal flagellum has a basal plate and the flagellum has four 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 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'' (''The Flies''); he gave the name ''Haematopota'', meaning "blood-drinker", to another common genus of horse-flies.

Biology

Diet and biting behavior

Adult horse-flies feed on nectar and plant exudates, and some are important pollinators of certain specialised flowers; several South African and Asian species in the Pangoniinae have spectacularly long probosces adapted for the extraction of nectar from flowers with long, narrow corolla

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