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Family Tabanidae (Horse flies, clegs & deer flies)

Identification: Stout flies with the 3rd antennal segment annulated but without a style. Eyes very large and extended sideways. Antennae extend forwards. Proboscis is adapted for piercing in the female. Antennae may be short with base of flagellum greatly enlarged (subfamily Tabaninae - horse flies &clegs ) or long with the base of flagellum not greatly enlarged (subfamily Chrysopinae - deer flies).


Biology & Disease Transmission: Tabanidae feed on the blood of vertebrates and are important insect biting pests of livestock. Their painful bites cause disturbance whilst grazing, which may reduce weight gain, milk yield and feed utilization efficiency. In some parts of the world they may also be disease vectors, for example equine infectious anaemia virus to horses, trypanosomosis (Trypanosoma evansi) to camels, and anaplasmosis (Anaplasma marginale) to cattle. Deer flies are responsible for cyclical transmission of the nematode Loa loa to man.

 

Tabanus bromius (band-eyed brown horsefly)

Identification: Greatly enlarged base of antennal flagellum indicates Tabaninae. T. bromius is a rather small species (body length of 13-15 mm) with yellowish brown and black markings on the abdomen. The eyes are bare and there is a characteristic single straight eye band; there is also a broad alula at base of each wing. Flies July-August and commonly feed on the blood of cattle and ponies. Distributed widely in northern Europe into Russia.

 

The first image shows a female T. bromius - the eyes are clearly separated. She was sitting on a fence near some horses, no doubt considering biting one of them. The second image shows a male T. bromius sitting on some bramble - the eyes meet at the top with little or no separation. Since the males do not feed on blood, his proximity to the horses was to mate one of the several females that were around. This species was shown by Böse et al. (1987)  to be a vector of Trypanosoma theileri, a ubiquitous but apparently harmless protozoan parasite of cattle.

 

These two images show the diagnostic single eye stripe of T. bromius. Its visibility or otherwise depends very much on the viewing angle. It can be seen clearly in both these shots, but much less so or not at all in the previous two images. These bands are generally not visible in dried specimens, so they may not be referred to in identification keys for tabanids.

 

The first image shows a female T. bromius on a window - one of seven that entered a house in a Sussex village on one hot day in June. Whether this was the result of a sudden mass emergence, or of ideal weather conditions for 'swarming' on that day, is unclear, but it is not uncommon phenomenon with tabanid species. They may have been entering the house because of the higher carbon dioxide concentration compared to ambient, although they showed no inclination to obtain a blood meal from the occupants. The second image shows a male T. bromius feeding on moisture/salts on the ground. Males will also take nectar from flowers, as will the females of many species. However Krcmar & Maric (2010)  have shown that at least one blood meal is essential for females of this species for egg maturation.

 

Hybomitra bimaculata (Hairy legged horsefly)

Identification: Greatly enlarged base of antennal flagellum indicates Tabaninae. Unlike Tabanus spp., Hybomitra spp. have hairy eyes. H. bimaculata has three characteristic stripes on each eye (see below). Upper parts of tibia are orange; long hairs on the tibia of the middle leg; abdomen is usually dark grey with clearly marked whitish triangles along the dorsal midline. 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;

 

The first image shows a female Hybomitra bimaculata sitting on the white paintwork of a car. It had been attracted to the moving vehicle and settled when it stopped. The second image is a close-up of the face showing the densely hairy eyes characteristic of the genus.

This image shows the most characteristic feature of Hybomitra bimaculata - three stripes on each eye.

 

The small swarm of female H. bimaculata that had been attracted to the moving car had a choice of colours for settling - white (the bodywork), black (the tyres and runner seals) and red (the brake lights). Black and red seemed to be their preferred colours, with fewer settling on white than would expected if they showed no preference. Bracken et al. (1962)  found that all tabanid species in his area were attracted to black and red spheres, but most were not attracted to white spheres. Browne and Bennett (1980)  reported that Hybomitra spp. (and Chrysops spp) were attracted to blue or red, but were consistently not attracted to black, yellow or white. Colour preferences have been exploited in the development of traps for tabanids.

 

Haematopota pluvialis (Common or Notch-horned Cleg)

Identification: Greatly enlarged base of antennal flagellum indicates Tabaninae. Haematopota species have the wings held roof-like over the abdomen when at rest, not spread out in a V-shape; wings have a characteristic pattern of 'rosettes'. H. pluvialis has pale brown wings; antennae partly reddish-yellow; female has distinctively patterned eyes and an apical notch on the first antennal segment. Can be found in a wide range of habitats from May to October. Distributed from Europe to Russia and China; the commonest species of tabanid in UK.

 

The first image shows a male H. pluvialis perched on vegetation. Note the large eyes which meet on top of the head, with eye stripes restricted to the lower part of the eye. The third antennal segment is reddish near the base. The second image shows a close-up of the eye of a female H. pluvialis - the eyes do not meet on top of the head, and eye stripes extend over most of the eye.

 

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 (Krcmar, 2004 ). Bites from this species can be quite painful and the flies are remarkably resistant to being killed by hitting them. But the second image shows that they are not completely immune to a well aimed swat.

 

Chrysops caecutiens (Splayed Deerfly)

Identification: Base of antennal flagellum not enlarged indicates Chrysopinae. C. caecutiens has a distinctive pattern of spots on eyes; tibiae are blackish (although first tarsal segment is reddish brown); extensive clear patch near anal margin of wing ; no inverted yellow V mark on the second tergite; adults are usually associated with wet woodland and carr. Larvae live in mud at the water-side. The flight period is from mid May to early September, peaking from late June to late July. Widely distributed over western, central and northern Europe.

This shows the distinctive pattern of spots on the eyes of C. caecutiens. As with all tabanids, the pattern is much less evident in dried specimens.

 

Both these images show the blackish tibiae on all the legs which distinguish C. caecutiens from Chrysops relictus. These females were biting 'vigorously' in two East Sussex, UK woodlands. There is some evidence that this (and other) tabanid species may transmit Lyme disease (Borrelia sp.) to man (Stanek et al., 1987 ; Luger, 1990 ), although the main vector for Lyme disease is Ixodes ticks.

 

Chrysops relictus (Twin-lobed deerfly)

Identification: All tibiae are reddish; clear area near anal margin of wing suffused with black creating a clear spot; C. relictus has an inverted yellow V mark present on the second tergite formed by the twin black lobes. Found on damp moors and heathland and breeds in muddy banks. Widely distributed over western and northern Europe.

 

Although superficially similar to C. caecutiens, C. relictuscan be readily identified by its reddish tibiae. The first image shows a female taking a human blood meal through fairly thick jeans. We have included the second image since it clearly shows the twin black lobes on the abdomen. Mizell et al. (2002)  carried out a fascinating set of experiments to investigate the hierarchy of stimuli to induce attraction and settling of several Chrysops spp. - they were height, movement, speed, dimensions, color, size, and contrast.

 

Identifications & Acknowledgements

Whilst we try to ensure that identifications are correct, we do not warranty their accuracy. We have mostly made identifications from our photos of living specimens. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. Taxonomic information on the family is summarized from Richards & Davies (1977) . Stubbs & Drake (2001)  was used for species identification. Information on the distribution and biology of tabanids in the UK was obtained from Drake (1991) .

References

  •  Böse et al. (1987). Transmission of Trypanosoma theileri to cattle by Tabanidae. Journal of Parasitology Research 73 (5), 421-424. Abstract 

  •  Bracken, G.K. et al. (1962). The orientation of horse flies and deer flies (Tabanidae:Diptera): II. The role of some visual factors in the attractiveness of decoy silhouettes. Canadian Journal of Zoology 40 (5),685-695. Abstract 

  •  Browne, S.M. & Bennett, G.F. (1980). Color and shape as mediators of host-seeking responses of Simuliids and Tabanids (Diptera) in the Tantramar marshes, New Brunswick, Canada. Journal of Medical Entomology 17,58-62. Abstract 

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

  •  Krcmar, S. (2004). Ecological notes on Tabanus bromius L., and Haematopota pluvialis (L.), (Diptera: Tabanidae) of some flood areas in Croatian sections of the river Danube. Journal of Vector Ecology 29 (2),376-378. Full text 

  •  Krcmar, S. & Maric, S. (1987). The role of blood meal in the life of haematophagous horse flies (Diptera: Tabanidae). Periodicum biologorum 112 (2), 207-210. Full text 

  •  Luger, S.W. (1990). Lyme disease transmitted by a biting fly. New England Journal of Medicine A 322 (24), 1752 (Jun 14). Full text 

  •  Mizell, R.F. et al. (2002). Trolling: a novel trapping method for Chrysops spp. (Diptera: Tabanidae).Florida Entomologist 85 (2), 356-366. Abstract  Full text 

  •  Richards, O.W. & Davies, R.G. (1977). Imms' General Textbook of Entomology. 10th Edn. Chapman & Hall, London.

  •  Stanek, G. et al. (1987). Epidemiology of borrelia infections in Austria. Zentralbl Bakteriol Mikrobiol Hyg A 263 (3), 442-9. Abstract 

  •  Stubbs, A.E. & Drake, M. (2001). British Soldierflies and their Allies. British Entomological and Natural History Society.

Last updated 3 January 2013