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 Family Tabanidae (Horse flies, clegs & deer flies)

Identification: These are stout flies of medium to large size. The eyes are very large and extended sideways, often with bands or patterns when alive. In males the eyes meet or almost met on top of the head. In the females the eyes are well separated. The proboscis is adapted for piercing in the female, and for nectar feeding in both sexes. The antennae extend forwards with the 3rd antennal segment annulated but without a style. In some genera, the wings are patterned. Wing veins R4 and R5 are widely splayed either side of the wing tip with R5 converging on vein M1 (for a summary of the Comstock–Needham wing-vein naming system see Wikipedia. ) The squama is well developed forming a large flap adjoining the thorax.


There are about 4,500 species of Tabanidae worldwide. Female tabanids feed on the blood of vertebrates, and are important insect biting pests of livestock. Their painful bites cause disturbance to grazing livestock, which may reduce weight gain, milk yield and feed utilization efficiency. In some parts of the world they are disease vectors, for example passing equine infectious anaemia virus to horses, trypanosomosis (Trypanosoma evansi) to camels, and anaplasmosis (Anaplasma marginale) to cattle. Deer flies (Chrysops) are responsible for cyclical transmission of the nematode Loa loa to man. Both sexes of tabanids feed on nectar from flowers, and are important pollinators of some species.

 

Subfamily Chrysopinae

Identification: The antennae have four terminal segments, or fewer making a total of not more than seven antenal segments.  

Genus Chrysops (Deer flies)

Identification: The antennae are long with the base of flagellum not greatly enlarged. The wings have dark bands or are extensively blackish. Tergite 2 is often yellow with a black marking, or the abdomen is mostly black. The eyes of Chrysopinae are especially distinctive being bright or bronzy green with a number of dark spots.

  Chrysops caecutiens (Splayed deerfly)

Identification: Chrysops caecutiens is a medium-sized deerfly with a body length of 9-10 mm. The female has the first two abdominal tergites yellow, with a 'splayed' black marking usually in the form of two crossed straps (see first picture below). These black markings are sometimes much reduced or may expand to make tergite 2 mainly black. There is an extensive clear patch near the anal margin of the wing. Ventrally the first two segments of Chrysops caecutiens have a black median stripe (see second picture below).

 

At least the distal half, and all of the middle tibiae are usually black (see first picture above), although the first tarsal segment is reddish brown. The second picture above shows the red and green reflections of the eyes with a distinctive pattern of spots. As with all tabanids, the pattern is much less evident in dried specimens. The male Chrysops caecutiens has extensively darkened wings. It also has black abdominal tergites, although the sides of tergites 1 and 2 may be narrowly orange. The face has large bare spots almost meeting in the middle line and a distinctive pattern of pale-dusted patches occupying about one-third of the area.

The splayed deerfly is found in wet woods and the shaded parts of bogs and marshes. It is widely distributed over western, central and northern Europe. In Britain Chrysops caecutiens is most frequent in the south, but becomes scarce in northern England and is rare in Scotland. The flight period is from mid May to early September, peaking from late June to late July.

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  Chrysops relictus (Twin-lobed deerfly)

Identification: Chrysops relictus is a medium-sized deer fly with a body length of 8-10.5 mm. It has a pair of diverging twin black lobes on the second abdominal tergite, uniting at the base to form an inverted yellow V mark (see first picture below). This distinguishes Chrysops relictus from Chrysops viduatus, which has a single (quadrate) roughly square or rectangular spot, of variable size. The clear area near the anal margin of wing is suffused with black, creating a clear spot.

 

Chrysops relictus has all its tibiae reddish-yellow, clearly visible on the second picture above. This distinguishes it from Chrysops caecutiens which has the middle tibiae black. The male also has a pair of diverging lobes on the second tergite, although not as strongly divergent as in the females. The wing beyond the dark median band has a narrow clear band or band of white spots (see picture above) and is then diffusely dark near the wing margin. The sides of tergite 2 are conspicuously reddish-yellow and the mid-tibiae are entirely reddish-yellow. This distinguishes males of Chrysops relictus from males of Chrysops caecutiens, which have sides of tergite 2 only narrowly yellow at the sides and the mid-tibiae black.

The twin-lobed deerfly is found on damp moors and heathland. It is widely distributed over western and northern Europe. In Britain it is often frequent in the Midlands and all of southern England, but is present right up into the Scottish Highlands. Chrysops relictus flies from mid-May to mid-September peaking in late June and July.

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  Chrysops viduatus (Square-spot deerfly)

Identification: Chrysops viduatus is a medium-sized deerfly with a body length of 8.5-10 mm. The female Chrysops viduatus has only a small quadrate spot at the base of the second tergites (see pictures below). This may be slightly bilobed, triangular or heart shaped and does not usually extend to the hind margin of the tergite. The hind tibiae are entirely reddish-yellow. The wing is clear behind the sub-apical spot up the wing margin.

 

The male (not pictured here) is similar to the male of Chrysops relictus, but has no grey-brown shading near the hind margin of the wing. Chrysops viduatus has the second abdominal segment yellow with a large well-defined quadrate black spot. The middle tibiae are reddish yellow much like Chrysops relictus, but the fore and hind tibiae are generally dark. The facial bare spots are large, almost meeting in the middle line.

Chrysops viduatus occurs in wet meadows, mires, fens and wet woodlands. It may be very common in valley mires. It is found throughout Europe into middle Asia. It is on the wing from late May to September, peaking in July.

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Subfamily Tabaninae

Identification: These are medium to very large flies, 10-30 mm long. The greatly enlarged base of antennal flagellum is characteristic of this subfamily. Their eyes are often brownish but may be irridescent, with markings often in the form of horizontal bands.

 

Genus Hybomitra

Identification: These are medium-sized to large horseflies without wing markings. The eyes are hairy as can be seen in the first picture below. There is a raised ocellar tubercle also visible in the picture.

Both the male and female of most of the Hybomitra have three stripes on each eye as shown in the second picture above.

  Hybomitra bimaculata (Hairy legged horsefly)

Identification: Hybomitra bimaculata is a medium-large horsefly, with a body length of 13-16.5 mm. The female has a number of different colour forms. Probably the commonest has the abdomen dark grey with clearly marked whitish triangles along the dorsal midline (= form bisignata) (see first picture below). In a second form there are lateral reddish spots on the abdomen which reach to the third segment (= form collini). In another form of Hybomitra bimaculata the lateral reddish spots on the abdomen, stop short on the second segment (= form bimaculata)

 

The multiple abdominal colour forms of the female Hybomitra bimaculata can make identification tricky. Useful distinguishing features are:

  • the upper parts of the tibiae are orange and
  • there are unusually long hairs on the anterior and posterior surfaces of the mid tibiae (see second picture above).

It is active from May to August in woodland edge habitats and sheltered fens and marshes, especially heath woodland. Distributed widely in Europe, Russia, Mongolia, China and Japan;

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  Hybomitra ciurea (Yellow-horned levels horsefly)

Identification: Hybomitra ciureai is a medium to large horsefly with a body length of 14.5 mm. The female has extensive orange side markings on the abdomen extending from tergite 1 to tergite 4 (see first picture below). The extent of the orange side markings distinguishes Hybomitra ciureai from Hybomitra solstitialis and some forms of Hybomitra bimaculata, which only have orange side markings on tergites 1-3 or 1-2.

 

The bases of the antennae (antennal segment 1) are orange - hence the name "yellow-horned levels horsefly" (see second picture above). This character can be used to distinguish Hybomitra ciureai from another much commoner orange Hybomitra, Hybomitra distinguenda, which has the bases of the antennae grey-black. A more reliable way to separate females of these two Hybomitra species is to examine the colour of the hairs on the lateral thirds of the second tergite. The female Hybomitra ciuraei has distinct areas of black hairs on the orange ground colour, whilst female Hybomitra distinguenda has only orange hairs.

The male of Hybomitra ciureai (not figured here) has the first antennal segment reddish-brown. The upper facets of the eye are bigger than the lower ones and sharply segregated. The middle stripe of the abdomen is more brownish, less strongly defined and sometimes interrupted.

The flight period of Hybomitra ciureai is mid-June to mid-August. Hybomitra ciureai is common over many parts of Europe through to Russia, China and Mongolia, but is considered rare in Britain and is an RDB3 species (red data book species, vulnerable). It was formerly thought to be restricted to the Essex coast, but is now known to be found on grazing marsh in several south eastern coastal areas from Norfolk round to Hampshire.

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  Hybomitra distinguenda (Yellow-horned levels horsefly)

Identification: Hybomitra distinguenda is a medium to large horsefly with a body length of 15-18 mm. It has extensive orange side markings on the abdomen extending from tergite 1 to tergite 4 (see first picture below). The extent of the orange side markings distinguishes Hybomitra distinguenda from Hybomitra solstitialis and some forms of Hybomitra bimaculata, which only have orange side markings on tergites 1-3 or 1-2. The eyes of the female of Hybomitra distinguenda are green and have three reddish bands (see second picture below).

 

Hybomitra distinguenda can be confused with another orange Hybomitra: Hybomitra ciuraei. The only reliable way to separate them is to examine the colour of the hairs on the lateral thirds of the second tergite. In Hybomitra distinguenda they are entirely pale haired over the orange ground colour (or with only an odd dark hair), as can be seen in the picture below. Hybomitra ciuraei has similar orange side markings, but has patches of pale and dark hairs on the lateral thirds of the second tergite. The presence of many golden hairs on the lateral third or more of the abdominal dorsum gives female Hybomitra distinguenda the bright appearance referred to in the English name. The female may have dark hairs on the orange areas near the midline.

The male (not pictured here) has a narrow black stripe on the abdomen tapering to the third tergite. The lateral orange areas of the male are extensively covered with black hairs with only a few yellow hairs, in sharp contrast to the female. The first antennal segment is grey-black and the eyes have the upper facets somewhat larger than the lower, but not sharply segregated.

It is found through most of Europe and in Russia, Mongolia, China and Japan. Hybomitra distinguenda is a common species throughout Europe inhabiting various types of biotypes. Its habitats include wet heath, bog, wet woodland edge and wet meadows. The flight period early June to late August, peaking in early to mid July . The bright horsefly is widespread in Britain and Ireland, although it is scarce in the north.

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Genus Atylotus

Identification: These are small to medium-sized horseflies with clear wings. The eyes are yellowish or pale green to grey with one or more narrow bands.

The antennae are entirely orange although there may be light grey dusting on the first two antennal segments. The femora are often extensively orange. The males have hairy eyes but those of females are weakly haired or bare and there is a raised ocellar tubercle. The bare patches on the female frons are either weakly developed or completely absent.

  Atylotus rusticus (Hairy legged horsefly)

Atylotus rusticus is a medium-sized species with a body length of 12 mm. Both sexes are ash-grey with very inconspicuous pale yellow hairs on the thorax. The mainly bare thorax distinguishes Atylotus rusticus from Atylotus fulvus, which has abundant vivid golden yellow hairs on the thorax. The abdomen of the four-lined horsefly has light and dark hairs which form four indistinct longitudinal dark stripes (see first picture below). The ground colour of the abdomen is indistinctly reddish-yellow, mainly on the second segment.

   

Both sexes of Atylotus rusticus have the femora black except for pale tips, as can be seen in the second picture above. This distinguishes Atylotus rusticus from Atylotus fulvus and Atylotus latistriatus, both of which have extensively pale femora. The eyes of both males and females are pale green in life and have a more or less clearly marked narrow reddish band on the eye (see second picture above).

Atylotus rusticus is widely distributed and often common in mainland Europe. In Britain the four-lined horsefly used to occur commonly in Cambridgeshire, but apparently died out when the fens were drained. It is now very rare with RDB1 status (red data book species, rare) but it still occurs in East Sussex, where it is found in the coastal grazing marshes between Lewes and Bexhill, and on the Hampshire coast at Farlington Marshes. Flower-seeking adults may be found peripheral to these sites. More recently Atylotus rusticus has been reported in the Central Weald, in Long Herdon and Grange Meadows Reserve, Buckinghamshire, at Otmoor in Oxfordshire and in East Kent. The flight period is in June and July.

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Genus Tabanus

Identification: This is a large and rather ill-defined genus. The eyes are completely bare and there is no raised ocellar tubercle. There are hundreds of species worldwide which are often arranged in species groups.  

Tabanus bromius (Band-eyed brown horsefly)

Identification:Tabanus bromius is a medium-sized species with a body length of 13-15 mm. Both sexes (female shown below) have a dark, hairy abdomen with three longitudinal rows of yellowish- or greyish-brown spots. The front corners of tergite 2 are pale yellow with yellow hairs The overall appearance is rather variable ranging from a yellowish form to a blackish form. The mesonotum of Tabanus bromius is gray with five indistinct longitudinal lines.

 

The wing alula is broad. The eyes in both sexes are bare and greenish, with a characteristic single straight violet-red eye band shown in the second image above. Its visibility or otherwise depends to some extent on the viewing angle, and it is not generally visible in dried specimens. The male has no distinct zone of small facets along the hind edge of the upper part of the eye and the subcallus is entirely dusted.

Tabanus bromius flies in July-August and commonly feeds on the blood of cattle and ponies. It is distributed widely in northern Europe into Russia, the Near East and North Africa. In Britain it is relatively common throughout southern England, rare in northern England and unknown in Scotland.

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  Tabanus sudeticus (Dark giant horsefly)

Identification: Tabanus sudeticus is a very large rather dark species (body length about 25 mm) with small equilateral pale median abdominal triangles which do not reach the foregoing tergites, and (usually) little or no lateral reddish colour on the abdomen. These characteristics should distinguish Tabanus sudeticus from the very similar Tabanus bovinus, which has the abdomen distinctly reddish-orange at the sides and median triangles usually longer and reaching the foregoing tergite. In addition the tergites of Tabanus sudeticus have black or dark brown bands, whilst the tergites of Tabanus bovinus have brown or pale reddish-brown bands.

 

The first picture above shows a typical, strongly marked Tabanus sudeticus sitting on black cloth. The second picture shows a more reddish specimen captured in the New Forest, Hants in 1964. The additional characteristics detailed below enabled us to confirm that this more reddish one is also Tabanus sudeticus. The 3rd antennal segment of Tabanus sudeticus is reddish-brown on the basal part (including the dorsal tooth) and blackish brown apically, with the antennal flagellar segments black. On the underside, sternite 3 of Tabanus sudeticus has a full width dark band. In life the eyes of Tabanus sudeticus are blackish-brown with a coppery sheen. The parafacials have abundant black hairs and there are no eye bands.

Males of Tabanus sudeticus (not shown here) have the abdomen extensively yellow-orange. The facets in the upper two thirds of the compound eye of the male are, with the exception of those on hind margin, at least four times the size of the rest.

The dark giant horsefly is distributed widely in northern Europe into Russia. In Britain it mainly lives in boggy areas in the north and west, although it is also quite common in the New Forest.

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Genus Haematopota

Identification: Haematopota species have the wings held roof-like over the abdomen when at rest, not spread out in a V-shape. The wings have a characteristic pattern of 'rosettes'.

  Haematopota pluvialis (Common or Notch-horned Cleg)

Identification: Haematopota pluvialis has pale brown wings. The antennae are partly reddish-yellow and have an apical notch on the first antennal segment. The female has distinctively patterned eyes.

 

The first image shows a female Haematopota pluvialis taking a human blood meal. Flight (and hence feeding) activity of Haematopota pluvialis is dependent on a sufficiently high humidity and temperature. Bites from this species can be quite painful and the flies are remarkably resistant to being killed by hitting them. The second image shows a close-up of the eye of a female.

Haematopota pluvialis can be found in a wide range of habitats from May to October. It is distributed from Europe to Russia and China and is the commonest species of tabanid in UK.

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Identifications & Acknowledgements

Whilst we try to ensure that identifications are correct, we do not warranty their accuracy. We have made identifications from our photos of living and preserved specimens using Stubbs & Drake (2014) . Taxonomic information is summarized from Oldroyd (1969)  and Stubbs & Drake (2014) . Further information on the distribution and biology of tabanids in the UK was obtained from Drake (1991) . Any errors in identification or information are ours alone, and we would be very grateful for any corrections.

References

  •  Drake, C.M. (1991). Provisional atlas of the Larger Brachycera (Diptera) of Britain and Ireland. Biological Records Centre, Huntingdon, UK. Full Text 

  •  Oldroyd, H. (1969). Handbooks for the identification of British insects. Diptera Brachycera Section (a) Tabanoidea and Asiloidea. Royal Entomological Siociety of London, London.

  •  Stubbs, A.E. & Drake, M. (2014). British Soldierflies and their Allies. British Entomological and Natural History Society, Reading.

Last updated 28 November 2014