SUMMARY FOR 2022

The undoubted highlight of the 2022 survey was the re-discovery of Hybomitra lurida (Fallén) (the ‘Broad-headed Horsefly’) in the Cheshire Plain area. This finding was significant, as there was concern that it could possibly be extinct in the region (and England as a whole) due to factors mentioned in the report for 2018 (Grayson, 2019). Adding further significance, the finding of a female at Basin Mire B01 on 14th June 2022 was the first record of Hybomitra lurida from the Delamere Forest.

The other main priority species, Atylotus plebeius (Fallén) (the ‘Cheshire Horsefly’), was not found at any additional sites to those where it was found during the surveys of 2018 and 2019. This in itself was significant, as it was possible in 2022 to spend more time on potentially-suitable mires during the flight-period of Atylotus plebeius and during optimum weather conditions, yet no additional Atylotus plebeius sites were found. As was the case in 2018 and 2019, Atylotus plebeius was present on three basin mires on Little Budworth Common, and it was also seen on Wybunbury Moss. It was not seen on Shemmy Moss; however, in mitigation, not much time was spent on Shemmy Moss during 2022. Observations of Atylotus plebeius made during the evening of 15th June 2022 backed-up two previous behavioural observations. Firstly, both sexes usually choose the following ways of escaping danger – either fly away rapidly, or quickly drop down into bog vegetation such as Vaccinium oxycoccos (Bog Cranberry). Secondly, as dusk approaches, both sexes tend to make short (average 5 metres) lazy flights between perching points, which are generally on the flower-heads of Calluna vulgaris (Heather), or on the stems of fine bog grasses. The final perch for passing the night is usually on one of the upper shoots of heather, but not at the top; or if on fine bog grasses, is usually three-quarters of the way up the stem – in both cases, the flies perch head-downwards and remain motionless.

Although the overall Cheshire Plain area Tabanidae study results from the years 2018, 2019 and 2022 are not entirely comparable, overall numbers of Haematopota pluvialis (Linnaeus) (the ‘Notch-horned Cleg’) (an average of 6.5 individuals per survey day in 2022) were much reduced from those of the baseline 2018 survey (when an average of over 19 individuals were recorded per survey day), and the 2019 survey (when nearly 11 individuals were recorded per survey day).

The overall numbers of Tabanidae individuals recorded per survey day also reduced between 2018 and 2022. The average number in 2022 was 16.71; in 2019 the average number was 20.50; and in 2018 the average number was 25.05. In all years, there were days of inclement weather when no horseflies were found, and also days that were outside the season for horseflies in the Cheshire Plain area; therefore, on days when horseflies were found, they often occurred in far greater abundance than the aforementioned average numbers.

In contrast to reduced numbers of Haematopota pluvialis compared with the 2018 survey, the numbers of Chrysops viduatus (Fabricius) (the ‘Square-spot Deerfly’) and Hybomitra bimaculata (Macquart) (the ‘Hairy-legged Horsefly’) increased. In 2018, 33 Chrysops viduatus individuals were recorded; this number increased to 44 in 2019 and to 48 in 2022. In 2018, 26 Hybomitra bimaculata individuals were recorded (from 21 survey days); this reduced to 17 in 2019 (from 12 survey days), but increased to 54 individuals in 2022 (from 14 survey days).

Three further Tabanidae species were found during the 2022 survey. Chrysops caecutiens (Linnaeus) (the ‘Splayed Deerfly’) was found in larger numbers (13) than in 2019 (7) and 2018 (4). As with the earlier surveys, Chrysops relictus Meigen (the ‘Twin- lobed Deerfly’) was rarely found (6 individuals in total), which is unsurprising, as this is mainly a marshland species, that was only found on the basin mires when marshland was also included onsite or occurred nearby. Hybomitra distinguenda (Verrall) (the ‘Bright Horsefly’) was recorded in similar numbers to the earlier surveys (12 in 2022, 14 in both 2018 and 2019).

The objectives of the 2022 survey were achieved satisfactorily; therefore, unavoidable deficiencies of the 2018 and 2019 surveys were addressed fully, and the Cheshire Plain area study of Tabanidae that commenced in 2018 was concluded successfully.

In addition to the report, the raw data is available to download here (submitted to iRecord).

Ref. Diptera

Ref. True Flies

Published June 2023