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Identification & Distribution:

Identification

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. They may have a clearly marked narrow reddish band on the eye (see first picture below).

 

Alternatively, the band may be very faint as shown in the second picture above and in pictures on bioimages. 

Distribution & Seasonal Occurrence

In Britain the four-lined horsefly is now very rare with RDB1 status (red data book species, rare). Atylotus rusticus used to occur commonly in Cambridgeshire, but apparently died out when the fens were drained. It still occurs in East Sussex, where it is found in the coastal grazing marshes between Lewes and Bexhill (Grayson & Stubbs, 2008 ), 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 (Stubbs, 2004 ), in Long Herdon and Grange Meadows Reserve, Buckinghamshire (Webb & Smith, 2004 ), at Otmoor in Oxfordshire (Storey & Post, 2006 ) and in East Kent (Grayson, 2009 ). The flight period is in June and July.

Blood feeding

It has been suggested that the four-lined horsefly is more interested in flowers than in biting people (see bioimages ). This may sometimes be the case, but it will nevertheless still take blood meals - and we have had them probe when presented with a human host, as in the picture below.

Kniepert (1980)  found that 15.2% of flies (N=46) had either fresh or digested blood in the midgut. 73.3% of flies tested positive for fructose (N=15) indicating recent nectar feeding. For comparison about 11% of female Tabanus bromius had fresh or digested blood in the midgut (N=5632), and over 47% had taken nectar (N=5007).

There appears to be no data on preferred hosts of Atylotus rusticus. They have been recorded as feeding on cattle, and cattle and horses are the most available host at least in their British haunts of coastal grazing marsh.

Nectar feeding & puddling

This species has been found around midday in hot sunshine feeding on flowers of Wild Carrot and thistles and resting on the ripening fruits of Curled Dock. Adults have been recorded nectar-feeding on umbellifers and thistles some distance from breeding sites on the higher parts of the South Downs (see bioimages ).

Breeding sites

In Britain Atylotus rusticus is reported to breed in muddy ditches and pond edges, where they prey on small organisms.

Trapping & odour attractants

It appears that no previous studies have been carried out to evaluate traps and odour baits for Atylotus rusticus. Using cow urine/acetone - baited NG2F traps (pictures below) we caught this species in small numbers in two locations in East Sussex, in a field on the Pevensey Levels and at Middle Farm on the edge of the Lewes Levels. (Brightwell & Dransfield, 2014 ).

References

  • Brightwell, R. & Dransfield, R.D. (2014). Survey of Tabanidae (horseflies) in southern England 2014. A preliminary survey of tabanids using odour-baited NG2F traps. 14 pp. Full text 

  • Grayson, A. & Stubbs, A.E. (2008). Observations of Atylotus rusticus (L.) (Dip.:Tabanidae) in Sussex during 2006. Entomologists Record and Journal of Variation 120(3), 120-122.

  • Grayson, A. (2009). Atylotus rusticus (Linnaeus, 1761) (Diptera, Tabanidae) new to East Kent.

  • Kniepert, F.W. (1980). Blood-feeding and nectar-feeding in adult Tabanidae (Diptera). Oecologia 46, 125-129. Abstract 

  • Storey, M.W. & Post, (2006). Recent records of Atylotus rusticus (Linnaeus, 1761) (Diptera, Tabanidae). Dipterists Digest (Second Series) 13, 21-22.

  • Stubbs, A. (2004). The horsefly Atylotus rusticus (L.) in the Central Weald. British Journal of Entomology and Natural History 17(1), 23.

  • Webb, J.A. & Smith, M.N. (2004). Atylotus rusticus (Linnaeus, 1761) (Diptera, Tabanidae) at the Long Herdon and Grange Meadows Reserve, Buckinghamshire. Dipterists Digest (Second Series) 10, 67-68.