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Identification & Distribution:

Identification Haematopota pluvialis is a small to medium-sized tabanid with a body length of 8-10 mm. The wings are pale mottled brown and the abdomen has a rather faint series of lateral pale spots on a dark background (see first picture below). The first antennal segment is rather bulbous, is partly shining black and has a strong sub-apical notch. The presence of the sub-apical notch is the best way to distinguish Haematopota pluvialis from Haematopota crassicornis, which has no notch.

 

The hairs on the apical two thirds of the female palps are sparse and mostly black. The third antennal segment is about 2 - 2.5 times as long as wide and is partly reddish-yellow (see second picture below). This also distinguishes Haematopota pluvialis from Haematopota crassicornis which usually has entirely black antennae.

The female Haematopota pluvialis has distinctively patterned hairy eyes - the eye stripes extend over most of the eye.

 

The first image below shows a male Haematopota 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 obviously orange at its base which distinguishes the species from Haematopota crassicornis in which it is normally entirely black. The second image above is a close-up of the eyes of the male viewed from above.

Distribution & Seasonal Occurrence

The Common Cleg can be found in a wide range of habitats including coastal marsh from May to October. In Britain it is the commonest species of tabanid from the south coast to the north of Scotland. It is also very common in Ireland, especially in boggy and upland districts. Haematopota pluvialis is distributed from Europe to Russia and China.

 

Biology & Ecology:

Resting behaviour & Swarming

Grayson (2001)  notes that whilst Haematopota pluvialis females are commonly encountered in the field, males are found much less often. Extensive sweeping and searching of sites where females occur only rarely produces any males. When they are located, they occur as either a single male, or group of males of usually no more than ten individuals. Favoured resting places for males are areas of tall grasses in relatively open positions, a few metres from water bodies. These resting places are no more than a few metres across, and the same areas are used by successive generations of males. Within the resting places, males rest on the floppy grass heads of tall grasses, or near the leaf tips, and make regular flights, either just above the grass heads or slowly between grasses, possibly searching for, or trying to intercept females. He also observed a group of male and female Haematopota pluvialis 'dancing' in the sky at Mersea Island, North Essex.

Blood feeding

Much as with other tabanids, most feeds of the common cleg probably come from cattle and horses. Liebisch (1987)  found that of 20 species of tabanids infesting cattle during the pasturing season, Haematopota pluvialis and Haematopota italica were the most abundant. Contrary to this, Titchener et al. (1981)  found only a few Haematopota pluvialis around cattle in south west Scotland.

There are of course innumerable accounts of Haematopota pluvialis biting man, especially in upland areas where clegs can turn a pleasant walk into an endurance course. Our own experience in the Scottish Highlands is that when the sun is out, the clegs bite; when the sun goes in the midges bite! Flight (and hence feeding) activity of Haematopota pluvialis is dependent on a sufficiently high humidity and temperature (Krčmar, 2004 ).

 

The first image above shows a female Haematopota pluvialis taking a human blood meal. 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. Grayson (1997)  reports that females may attack in numbers at sites where the species is common. He has found they prefer the torso and arms, especially the wrists, belly and crutch area.

Nectar feeding & puddling

Kniepert (1980)  found that only 4.3% of Haematopota pluvialis (N=1914) had either fresh or digested blood in the midgut. 59.1% of flies tested positive for fructose (N=1050) indicating recent nectar feeding. Compared to other tabanids, this was a low proportion with blood but a fairly typical proportion with evidence of nectar feeding.

Breeding sites

In captivity Haematopota pluvialis females have laid egg masses on the flowering heads of perennial rye grass (Cameron, 1930 ). In a pioneering study Burgess et al. (1978)  showed that Haematopota pluvialis lays its eggs on the surface of moist, but not wet, soil or at the base of grass-stems. Larvae were found in large numbers in damp soil in pasture-land, with a high preference for undisturbed old-field-pasture which has not been ploughed or fertilised. No larvae were found in marshy borders of streams, damp ground, leaf mould or rotting vegetation.

Trapping & odour attractants

Krčmar (2004)  used odour-baited Malaise traps to assess seasonal changes in abundance of Haematopota pluvialis in some flood areas of Croatian sections of the river Danube. Two peaks a year were observed. Krčmar et al. (2006)  found that many more female Haematopota pluvialis were collected in canopy traps baited with aged cow or horse urine than unbaited traps - the index of increase was about 20 times. For aged sheep or pig urine, the index of increase was about 15 times. However, Krčmar (2007)  found that 4-methylphenol and 3-isopropylphenol (generally considered to be the active chemicals in cow urine), were ineffective as attractants..

We have only caught low numbers of Haematopota pluvialis using cow urine/acetone - baited NG2F traps (pictures above and below) but in a variety of habitat types (Brightwell & Dransfield, 2014 ).

Several of these Haematopota were caught as the trap was being set. There are two possible explanations for this, which are not mutually exclusive. Firstly our movement around the trap may have been a factor in activating the flies - once we left the area there were insufficient stimuli to attract the flies. Secondly it is possible (likely?) that the flies are 'sit-and-wait' blood suckers, and do not fly around much 'hunting' for prey. Once flies in an area are caught, some time will elapse before others enter the area.

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 

  •  Burgess, N.R.H. et al. (1978). The immature stages of the common cleg Haematopota pluvialis L. (Diptera: Tabanidae). J. roy. Army med. Cps. 124, 27-30.

  •  Cameron, A.E. (1930). Oviposition of Haematopota pluvialis Linne. Nature 126, 601-602.

  •  Grayson, A. (2001). Notes on the behaviour of males of Haematopota crassicornis Wahlberg and Haematopota pluvialis (Linnaeus). Larger Brachycera Recording Scheme Newsletter 19.

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

  •  Krčmar, 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 

  • Krčmar, S. et al. (2006). Response of Tabanidae (Diptera) to different natural attractants. Journal of Vector Ecology 31(2), 262-265. Full text 

  •  Liebisch, A.(1987). Vector Biology of Flies on Grazing Cattle in Germany. Veterinary Medicine and Animal Science 45, 109-115.

  •  Titchener, R.N. et al. (1981). Flies associated with cattle in south west Scotland during the summer months. Researches in Veterinary Science 30 (1), 109-113. Abstract