A survey of horseflies (Diptera: Tabanidae) on mires in the Cheshire Plain area during 2019

Principal Aims and Priority Species

The project aimed to satisfactorily bring to a conclusion a programme of extensive surveying for horseflies (Diptera: Tabanidae) on Cheshire Plain area mires and former mire sites that had commenced in 2018 and was the subject of a report by Grayson (2019). The current report should be regarded as both a supplement and a companion to that original report.

Permissions were obtained to visit a large number of Cheshire Plain area mires during 2018, but it was not physically possible to visit them all during the optimum flight-period for most British horseflies; this generally being from the second week in June to mid-July (in a typical year). In the case of sites that were not visited during this optimum period in 2018, the follow-up fieldwork of 2019 aimed to address this inadequacy by re-visiting such mires and their immediate vicinities during this optimum period for the occurrence of adult horseflies.

As was the case with the 2018 survey, the entire horsefly family (Tabanidae) were the priority; and within this group, the two main priority species for the 2019 project remained the same as for the project of 2018, i.e. the horseflies Atylotus plebeius (Fallén, 1817) and Hybomitra lurida (Fallén, 1817) [respectively, the ‘Cheshire Horsefly’ and ‘Broad-headed Horsefly’ of Stubbs & Drake (2001 & 2014)]. A follow-up investigation was needed for Hybomitra lurida in particular, as it was not found in the Cheshire Plain region during 2018.   The 2019 project aimed to increase the chances of re-discovering this horsefly in the region (if it remained extant) by paying two visits (in the late May to mid-June period) to the extensive tracks of mire habitats which are collectively designated as The Fenn’s, Whixall, Bettisfield, Wem and Cadney Mosses Complex SSSI, plus visits to other plausible sites, e.g. Wybunbury Moss, during the same period.

Atylotus plebeius was rediscovered on quaking bogs in three widely-separated localities in the broad Cheshire Plain area during 2018. The 2019 project aimed to include occasional brief visits to these sites, in order to carrying out some degree of monitoring and observations on this diminutive horsefly; but, for the most part, time and effort in 2019 would be given over to trying to discover if Atylotus plebeius was present on any additional mires in the Cheshire Plain region, particularly those which contained some areas of quaking bog habitat. The provisional list of sites for further investigation for this species included the aforementioned SSSI complex, and the following mires which were mentioned by Grayson (2019) as being probably the most likely to deserve future investigations for the possible occurrence of Atylotus plebeius: Barnsbridge Basin (SJ 5420 7190), Black Lake (SJ 5373 7091), Brackenhurst Bog (SJ 5956 6983), Boggy Pool (SJ 5970 6910), Gull Moss (SJ 6011 6871), Hogshead Moss (SJ5842 6952), Lily Pool (SJ 5956 6925) and South Moss (SJ 5937 6863).

Aside from Tabanidae, the main priority species for the 2019 survey were the small black hoverfly Orthonevra intermedia (Lundbeck, 1916) and the picture-winged crane-fly Idioptera linnei Oosterbroek 1992. The mires of the Cheshire Plain region are of national importance to these species; indeed, Orthonevra intermedia, is not known elsewhere in Britain. It was added to the British list by Drake (2006) on the basis of specimens taken in the Delamere Forest at Norley Moss and Barnsbridge Basin during 2003. The studies of 2018 (Grayson, 2019), were able to add a further Delamere Forest locality (Black Lake), and two sites in the broad Abbots Moss area (Hogshead Moss and Shemmy Moss).

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