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Twin-lobed deerflyOn this page: Identification Distribution & Seasonal Occurrence Resting behaviour & Swarming Blood feeding Nectar feeding & puddling Breeding sites Trapping & odour attractants
Identification & Distribution:
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 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 first picture below. This distinguishes it from Chrysops caecutiens which has the middle tibiae black.
Picture of male courtesy of James Lindsey, at Ecology of Commanster, CC-BY-SA-3.0 via Wikimedia Commons
The male (second picture above) 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.
Distribution & Seasonal Occurrence
The twin-lobed deerfly is found on damp moors and heathland. In Britain it is often frequent in the Midlands and all of southern England, but is present right up into the Scottish Highlands. It is widely distributed over western and northern Europe. Chrysops relictus flies from mid-May to mid-September peaking in late June and July.
Biology & Ecology:
Resting behaviour & Swarming
Males have been seen swarming at a lake margin Oldroyd (1939).
There is very little detailed information on the host range of Chrysops relictus, nor it seems of any other European Chrysops species. Chrysops relictus is known to feed on large mammals including cattle, horses and deer Davies et al. (1971) caught Chrysops relictus and several other tabanid species off cows in Norway.
However, it is also much more ready to bite man than many tabanid species. Grayson (1997) reports that females attack in ones and twos, and almost invariably encircle the top and back of the head several times before alighting. Unlike Chrysops caecutiens they may alight and bite on the torso and arms as well as on the hair. The image below shows a female taking a human blood meal.
Gouteux et al. (1989) found that two African species (Chrysops silacea and Chrysops dimidiata) took 89-90% of their blood meals from humans, and the rest from hippopotamuses, rodents, wild ruminants and monitor lizards. None was from domestic animals despite the availability of sheep and goats. Chrysops hirsuticallus in California preferred feeding on cattle and deer, but also fed on small mammals (Lane & Anderson, 1982 ).
Nectar feeding & puddling
Males have been seen visiting the flowers of water mint and water-dropwort (Oldroyd (1939) )
Chrysops relictus larvae develop as predators in wet mud and debris at the margins of streams and pools. Oldroyd (1939) reports that pupae have been found in sand by a lake.
Trapping & odour attractants
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. The most important factors were, in order, height, movement, speed, dimensions, color, size, and contrast.
Some work has been done to test the effectiveness of different odour attractants for Chrysops relictus. In Croatia Krčmar et al. (2006) showed that canopy traps baited with aged cow, horse, sheep, or pig urine caught more Chrysops relictus (a total of 16 in 4 traps) than did the unbaited trap (0), but he found the differences were not statistically significant. Since the control (unbaited) traps failed to catch any of that species, no index of increase could be calculated. Similarly 4-methylphenol (one of the active chemicals in cow urine) increased the catch of Chrysops relictus from 2 to 34 but again the difference was not statistically significant. (Krčmar, 2007 ).
We have caught various Chrysops species using cow urine & acetone - baited NG2F traps in several habitat types in southern England (Brightwell & Dransfield, 2014 ). Catches of Chrysops relictus were highest in coastal grazing land, such as the Pevensey Levels and Rye Harbour (see photo below).