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NEYEDC improve and inform environmental decision making, conservation, land management and sustainable development in North and East Yorkshire through the collation, management, analysis and dissemination of biodiversity information.

The Natural History of Yorkshire in 100 Species

Explore the rich and diverse natural history of our region through the stories of 100 species, told by the people who know them best.

#77 Dark Giant Horsefly by Andrew Grayson

Meet Andrew Grayson, professional freelance invertebrate consultant!

Andrew Grayson has been a professional freelance invertebrate consultant since 2009. His previous profession was in the laundry industry, in which he worked for The Ryedale Laundry in Kirkbymoorside from 1978 until 2009. Since turning professional as an invertebrate consultant, Andrew has been involved with over 100 commercial projects carried out on behalf of a wide range of clients including organisations that are principally concerned with conservation, and companies that deal with the ecological aspects of planning applications. Although he has never lived outside Yorkshire, most of his commercial surveys have been in other counties.

Andrew is the author of two entomological books, viz. Flies in The Yorkshire Museum (Grayson, 1994) and The Horseflies of Yorkshire (Grayson, 1995), and is also the author, or co-author, of more than 100 papers published in various scientific journals and similar publications. His papers include species new to Britain, new to Ireland, and new to England; plus notes on exceptionally rare British species. His current volunteer posts include being Scheme Organiser of the national Oestridae Study Group, of which he was the founder; Recorder for most Insect orders for the Ryedale Natural History Society; and Recorder for Diptera, excluding Agromyzidae, for the Yorkshire Naturalists’ Union. He has held the latter two posts continuously since the mid-1990s.

Andrew can be contacted via email at andrewgrayson1962@live.co.uk.

The Dark Giant Horsefly Tabanus sudeticus is Andrew’s chosen species.

Choosing a single dipterous fly to feature in this blog from a list of approximately 4,500 species of Diptera that occur in Yorkshire (Grayson, 2024) was obviously not going to be absolutely straightforward; although, given its impressive size for a fly of bulky build, Tabanus sudeticus was inevitably one of the prime candidates for selection. Females measure up to 27mm in body-length, with an average wing-length of 20mm; furthermore, average-sized males are only slightly smaller. Tabanus sudeticus is exceeded in body-length and wing-length by only a few other British flies, most of which are crane-flies in Tipulidae and Pediciidae.

Tabanus sudeticus female, Dalby Forest, 15.07.2012, Ian J. Andrews

Tabanus sudeticus is mainly a northern and western species in Britain. In Yorkshire, it has mainly been recorded from the North York Moors area (records too numerous to enumerate here), where it breeds at several widely-separated upland bogs, and possibly in other wetlands. Adults are highly mobile, and females in particular often fly many miles from their breeding sites in search of blood-meals from large grazing animals and can occasionally be encountered in the towns and villages that line the southern edge of the North York Moors.

In the Yorkshire Dales area, Tabanus sudeticus has been found in recent years at Dent in 2024, Ingleton in 2018 and Low Bentham in 2013 and 2018. Another recent and interesting find was a male on foliage in a Strensall garden in 2022. This was particularly interesting because Tabanus sudeticus had not previously been recorded from any ‘lowland’ regions of Yorkshire.

The first published account providing evidence that Tabanus sudeticus occurs in Yorkshire was a report for the year 1887 by Ormerod (1888), in which a fly purporting to be Tabanus bovinus was clearly Tabanus sudeticus based on the excellent illustration provided and description given. Referring to this fly, Ormerod (1888) stated "last year one was forwarded to me on the 26th August, by Mr. James Carter, of Burton House, Masham, Yorks., with the observation that this large insect was occasionally found in the neighbourhood".

Andrew’s first encounter with Tabanus sudeticus was a female at rest on a fence-rail near the stream that flows from the southern end of Fen Bog in 1988. The following year, Helena Olsson gave him a barely-alive male she had found at the roadside in Thornton Dale. He subsequently observed both sexes of Tabanus sudeticus fairly regularly and widely in the North York Moors area, from Ashberry Pasture in the west, to boggy localities along the Scarborough to Whitby Road in the east, and as far north as Murk Mire Moss. When living in Kirkbymoorside, Andrew observed Tabanus sudeticus females occasionally entering the town and becoming trapped inside buildings, having entered through open windows or doors during hot weather conditions.

Recording and monitoring

Tabanus sudeticus male, Dalby Forest, 06.07.2017, Ian J. Andrews

Records of Tabanus sudeticus can be submitted to your LERC or submitted to iRecord. Alternatively, records can be submitted to Andrew as county recorder and submitted  andrewgrayson1962@live.co.uk. The appropriate national recording scheme is now called the 'Soldierflies & Allies Recording Scheme', the organiser of which is Martin Harvey - his email address is kitenetter@googlemail.com.

Further information and acknowledgements

NEYEDC would like to thank Andrew for his time and expertise in helping to create this blog.

NEYEDC