Key Information

Flight Period: Early June to Late July GB Rarity Status (2017): : Nationally Rare GB Threat Status (2017): : Endangered

Status Overview

Atylotus plebeius, The Cheshire Horsefly, was given a Great Britain (GB) Rarity Status of ‘Nationally Rare’ and a GB threat category of ‘Endangered’ in a recent review of the Larger Brachycera flies of Great Britain (Drake, 2017). A. plebeius was formerly listed as RDB1 in Shirt (1987) and Falk (1991). Indeed, this species has always been a very rare insect in the UK, having been recorded from a maximum of five separated localities since it was first found in 1911 (SRS, 2017).

UK site discovery years
Abbots Moss complex: 1911
Delamere forest: 1911
Wynbunbury Moss: 1956
Fenns / Whixall / Bettisfield Moss complex: 1969
Little Budworth Common: 1995

The precise location of the 1911 ‘Delamere Forest’ location is unknown. There are many mosses within the forest. The ‘Abbots Moss complex’ locality has only been more precisely recorded since 1996, when Andrew Grayson (AG) found a male and female on Shemmy Moss (a quaking bog). AG found the fly again at Shemmy Moss in 1999, which stood as the most recent UK record when the 2017 national status review was published.

Following the publication of the new status review, The Tanyptera Project made A. plebeius a ‘priority species’ and commissioned AG to undertake a landscape-scale survey of the Cheshire plain acid mires during the 2018 field season in order to establish the species current status and identify threats to remaining populations (Grayson, 2019). An exhaustive series of sites were visited and A. plebeius was found to still be extant at three widely separated localities: Shemmy Moss (SJ5968), Wynbunbury Moss (SJ6950), and three quaking bogs on Little Budworth Common, which are known as Central Moss (SJ58506574), East Moss (SJ58596570), and Whitehall Moss (SJ58786580). A. plebeius was not found at the extensive wetlands of Fenns, Whixall and Bettisfield Mosses on the Shropshire / Denbighshire border, and with no records since 1980, may now be extinct. In 1911, A. plebeius was recorded inside Delamere forest but virtually all quaking bogs here have since suffered catastrophic degradation apart from Black Lake and it’s likely also extinct at this locality. However, in recent years major bog restorative works have taken place in the Forest through the Delamere’s Lost Mosses Project (2013-2018), which offers hope that A. plebeius could re-colonise from nearby Shemmy Moss or Little Budworth Common should conditions become suitable.

In conclusion, AG (2019) states that whilst A. plebeius is likely restricted in the UK to pristine quaking bogs in the Cheshire Plain area and has only been found extant at three localities in the 21st Century, there is still potential for undiscovered populations. Sites considered to have the highest potential are listed in the report.

Habitat

In Britain, the fly is only known from pristine, genuine quaking bogs with a complete thick covering of Sphagnum and bog plants (e.g. Drosera and Vaccinium) forming a floating mat above permanent water beneath in glacial kettle-holes (Grayson, 2019). At the time of writing, the author is not aware of any larval information but they are likely to be semi-aquatic and predatory.

Little Budworth Common (Andrew Grayson 2018)

Shemmy Moss (Andrew Grayson 2018)

Wynbunbury Moss (Andrew Grayson 2018)

 

Life History

Largely unknown. In Britain, adults have been recorded active diurnally from early June to late July. There are no UK records of females taking blood meals (Stubbs and Drake, 2014). Manitoba traps set on occupied sites during the 2018 survey failed to attract females in search for a blood meal. Copulation and oviposition appear not to have been documented, and the larva remains undescribed. During the 2018 survey, AG observed a male preparing to roost, perched head-downwards on a patch of Calluna vulgaris (Heather) near the centre of a mire. Another behavioural observation from the survey described both sexes having a perchant for alighting upon, and crawling over, the unopened or dead flower-heads of Calluna vulgaris (Heather).

Recording / Identification

A. plebeius is fairly distinctive amongst the British Atylotus, and with experience can be recorded in the field so may be suitable for non-specialist volunteer surveillance and monitoring. See Stubbs and Drake (2014) for detailed information on identification. Amongst closely related species, it is the smallest with a body length of 9-10 mm and is ash-grey. The most similar species in appearance and ecology, A. sublunaticornis, is found on the continent but despite checks of A. plebeius specimens in UK specimens by AG, there is no evidence of UK occurrence. A. plebeius should be targeted in warm, sunny conditions during the peak flight period using an appropriate aerial / sweep net.

Conservation

The three known extant sites have legal protection as designated SSSIs and are managed for wildlife conservation:

Wynbunbury Moss – owned and managed by Natural England as a National Nature Reserve (NNR)
Shemmy Moss (part of the Abbots Moss complex) – owned by the Forestry England and managed by Cheshire Wildlife Trust
Little Budworth Common – owned and managed by Cheshire West and Chester Council

These sites must be considered as being of paramount importance for the survival of A. plebeius in Britain. Little Budworth Common could be considered the UK stronghold with three occupied bogs and where the fly was found in the largest numbers in 2018. At the time of the survey, A. Grayson judged the above sites as being in prime condition and will be for many years without any significant management interventions although scrub control should continue (e.g. pine and birch). There is no apparent threat of drainage (and consequential drying out of the bogs) under current management. Future warming from climate change could therefore also be considered a threat. According to GBIF (2020), A. plebeius is almost entirely restricted to Northern Europe, with the only outliers in southern Germany at >600 metres above sea level. The British population is otherwise at the extreme Southern end of it’s global distributional range and all UK occupied sites are <100 metres above sea level.

It is suggested by AG (2019) that creating open pools within these mosses could have a negative effect whereby there is an increase in larval predators from Odonata breeding but there is currently no evidence to support this.

Further Information

Go to 2018 survey report

References

Drake, C. M. (2017) A review of the status of Larger Brachycera flies of Great Britain. Species Status 29. Natural England Commissioned Report NECR192.

Falk, S. J. (1991) A review of the scarce and threatened flies of Great Britain (Part 1). Research & survey in nature conservation 39. Peterborough: Nature Conservancy Council.

Global Biological Information System (2020) Biological Records of Atylotus plebeius accessed 16th September 2020

Grayson, A. (2018) Atylotus plebeius (Fallén) (Diptera, Tabanidae) in Britain, including discoveries made during 2018. Dipterists Digest (Second Series) 25: 99-103.

Grayson, A. (2019) The status and distribution of the horseflies Atylotus plebeius and Hybomitra lurida on the Cheshire Plain area of North West England in 2018. Liverpool: Tanyptera Trust & National Museums Liverpool.

National Biodiversity Network Atlas (2020) Biological Records of Atylotus plebeius accessed 16th September 2020
RECORD (2017) Biological Records of Atylotus plebeius accessed in 2017.

Shirt, D.B. (1987) British red data books, number 2 insects. Nature Conservancy Council, Peterborough.

Soldierflies and Allies Recording Scheme (2017) Biological records of Atylotus plebeius accessed in 2017.

Stubbs, A.E. & Drake, C. M. (2014) British Soldierflies and their Allies. An illustrated guide to their identification and ecology: covering all flies (Diptera) in the the [sic] families Acroceridae, Asilidae, Athericidae, Bombyliidae, Rhagionidae, Scenopinidae, Stratiomyidae, Tabanidae, Therevidae, Xylomyidae and Xylophagidae. Reading: British Entomological and Natural History Society.

Taylor, M. (2000) A modern record of a Red Data Book 1 [Endangered] horsefly Atylotus plebeius (Fall.) (Diptera: Tabanidae) from Little Budworth Common, Cheshire (SJ585657). Journal of the Lancashire & Cheshire Entomological Society 124: 121-123.