#8 Slugs and Snails by Terry Crawford and Adrian Norris
Meet Terry Crawford and Adrian Norris, Yorkshire conchologists!
Terry Crawford and Adrian Norris have enjoyed much time together sharing their interests in slugs and snails and also their active involvements in the Yorkshire Naturalists’ Union and the Yorkshire Conchological Society.
Adrian (left) and Terry (right) at Malham Tarn in July 2011 when the YNU celebrated its 150th Anniversary. © Mary Crawford.
Terry has been interested in wildlife since before he started school. His father was an amateur freshwater algologist who roamed the Cheshire/Derbyshire borders at weekends with colleagues, carrying in khaki ex-army bags lots of fascinating equipment and cheese sandwiches provided by Terry’s mother. Terry was not allowed to accompany them and had to console himself with pottering around the garden observing the birds and collecting beetles. Years later at school he was required to undertake a study of plants or animals and, noting that nobody seemed to like them, he chose slugs. These and snails became his main focus and he contributed records to the 1976 Mollusc Atlas (Kerney, 1976). Terry came to Yorkshire in 1972 when appointed a population geneticist at the University of York. Work and family pressures meant that mollusc recording was much reduced although he retained his interest in moths and butterflies. In 1992 he chaired the Lepidoptera Study Group and continued to do so for most of the next 22 years, by when it had become the YNU Lepidoptera Group. He retired in 2006 and Adrian encouraged him to rekindle his interests in molluscs. Since 2010 he has been Chair of the Yorkshire Conchological Society and YNU Conchological Section, and he served as President of the YNU in 2009. You can contact Terry at terryjcrawford@btinternet.com.
Adrian was born in Hull and has been recording molluscs as a volunteer for over 50 years. He passionately believes that all records belong to everyone. Since the spring of 1967 when Adrian became the County Recorder, the distribution of slugs and snails throughout Britain has changed dramatically. He is especially fascinated by the arrival of new species into new areas but also equally interested in the disappearance of species which used to occur in Yorkshire. Adrian spent a decade in the early 2000s as National Recorder on behalf of the Conchological Society of Great Britain and Ireland having served as the Society’s President in 1984-85. Professionally, he worked for the Leeds City Museum for nearly 40 years starting as a technician under John Armitage (1900-1996) in the autumn of 1964, looking after worldwide collections of zoology and botany. He retired in June 2003 from the post of Senior Curator Natural Sciences and Ethnography with responsibility for the City Museum and its collection stores. Adrian was also active in museums internationally, having been a board member of the Natural History committee of the International Council of Museums. You can contact Adrian at adrianxnorris@aol.com.
Terry and Adrian’s chosen species are two of Yorkshire’s most interesting non-marine molluscs, the Fylingthorpe Slug Limax cf. dacampi and the Wall Whorl Snail Vertigo pusilla.
The Slug
An outstanding item of interest in recent years in the field of non-marine molluscs is a nationally new species of slug found in north-east Yorkshire. The Fylingthorpe Slug is the vernacular name given to this species by Ben Rowson in his book Slugs of Britain and Ireland. Identification, understanding and control (Rowson, 2014a). The Fylingthorpe Slug can be found on the NBN Atlas.
The original photograph sent by Marie to Terry on 10/09/12. Inset: the size of the specimen against Marie’s hand. © Marie Jeanne Perry.
Marie Jeanne Perry, a resident teacher at Fyling Hall School, a boarding school near Robin Hood’s Bay in north-east Yorkshire, was intrigued by extremely large slugs in the school grounds. She had been a biology student at University of York with a strong interest in natural history which Terry had encouraged. On the 10th of September 2012, she took a photograph of one of these slugs and e-mailed it to Terry who tried to identify it without success. Terry forwarded it to Adrian, but they could do no better than doubtfully try to shoehorn it into an undescribed variety of Leopard Slug or Great Grey Slug (Limax maximus), or even Great Britain’s largest slug, the Ash-Black Slug (Limax cinereoniger).
On the 25th of September, Terry and Adrian were joined by two people from The National Museum of Wales in Cardiff, Ben Rowson and Bill Symondson, to look for slugs in the Hackness area. Unfortunately, they were in such torrential rain that it was difficult to find any molluscs, so Terry phoned Fyling Hall School and Marie agreed to meet them all during her lunch-break and show them where to look for her slugs, in the hope that they could be identified. While Terry and Ben met up with Marie at the school, Adrian and Bill walked over to the woodland opposite the school. After only a few minutes, they turned up a very large slug, much larger than any other found in Britain, measuring over 130mm in length, and wider and bulkier, and visibly slightly bigger than the Ash-Black Slug. It even felt different, turgid and with very sticky mucus. Soon after, another example was found. Despite all the expertise on site, no one had ever seen anything at all like it before!
Amazingly, DNA studies (Rowson et al., 2014b) confirmed that the mystery slug was new to Great Britain, and that it has similarities to certain groups of Limax spp. found in the Apennines of central Italy and the southern Alps. It has been given the provisional scientific name Limax cf. dacampi until such time as it is formally described - the systematics and taxonomy of the genus are very poorly understood (Welter-Schultes, 2012). Terry and Adrian revisited the site several times over the next couple of years and noted that the ‘creamy-grey’ background colour seems constant, but that the black markings might be absent and that sometimes there is a noticeable keel and pale stripe extending up to the mantle (the area behind the head). A notable dissection feature is that its penis is longer than that of any other British slug; when extended, two to three times the body length (remember, slugs and snails are hermaphrodites!) (Rowson et al., 2014a). Whilst little is known of its biology, it is suspected that the Fylingthorpe Slug is largely subterranean, feeding on fungal mycelium except in the autumn, when it comes to the surface to breed.
So how did the Fylingthorpe Slug come to be here in Yorkshire? Fyling Hall, near the small village of Fylingthorpe, was built around 1819. Marble from the Central Apennines was used for some chimney surrounds, fireplaces and floors, and some small garden structures were also constructed from marble. The wife of the original owner was Italian and she laid out the garden and some of its plants, and this is still visible today. It was only in 1923 that the house was turned into a school by an inspirational teacher called Mable Bradley. Therefore, the origin of the slug is most likely from within the stones and plants imported from Italy when the house was first built. Terry and Adrian have looked in surrounding areas, but failed to find the slug outside of the school’s immediate vicinity. So, remarkably, this slug may have been introduced some 200 years ago and still survives today in this small area.
The Snail
Wall Whorl Snail found at Newfield Plantation on 19/05/12. © Terry Crawford.
From the large to the tiny, Terry and Adrian’s second species is the Wall Whorl Snail, Vertigo pusilla. The genus Vertigo is represented in Great Britain by 11 species, generally about 2mm in height, and difficult to find because of their minute size and rarity; only three species are reasonably widespread and frequent but in restricted habitats. Vertigo pusilla is one of the rarer species, but relatively easy to identify because it is sinistral - when viewed with the mouth of the shell facing you, then the mouth is on the left-hand side (see photo). One other Vertigo is sinistral, but it is exceptionally rare; the others are all dextral. The adult shell has five moderately convex whorls enlarging rapidly to produce a conical shape (Kerney & Cameron, 1979). Its typical habitat is mossy, ivy-covered walls protected by trees. You can find out more about the Wall Whorl Snail on the NBN atlas.
This minute snail is distributed mainly in north Lancashire and south Cumbria (VC69) and the adjacent areas of the Yorkshire Dales. In other areas of the UK there is a very small scattering of examples in more natural dry and undisturbed habitats (Crawford, 2012). Elsewhere in Yorkshire three small sites have recently been found in the north-east (VC62), otherwise, historically, records have come from the Magnesian Limestone strip. See Lindley (2016) for a Yorkshire overview.
The earliest record of this species was by Charles Ashford in 1854 in Went Vale (circa grid reference SE41), and presumably again in 1874 in Brockadale (grid reference approximately SE4917/5017). Additionally, a J.R. Hardy recorded it at Ackworth, which is located down the valley about 5km to the west of Brockadale, in September 1885 (grid reference SE41). It is important to remember that grid references were not introduced until the 1930s, so those quoted here (and in the NBN) are best estimates from the other information available. Locations could also be approximate in those days, e.g. using the nearest railway station for transport to the general area. Brockadale has regularly been visited by conchologists searching for other rare snails, and V. pusilla has not been found again. Consequently, these early records have mostly been put down to contamination from other sites and therefore have always been questionable. There is another record about 30km to the north on the Magnesian Limestone by F.G. Binnie in 1880, on an ivy-covered wall between Spofforth and Wetherby. The area has been searched in vain by Adrian and others.
Limestone wall, boundary to Newfield Plantation where Wall Whorl Snail was initially found. © Terry Crawford.
Having not been seen for decades on the Yorkshire Magnesian Limestone, it wasn’t until Terry attended a YNU Field Excursion to Fairburn Ings RSPB reserve in May 2012 that a new site was discovered for this rare snail on this geological strip. Terry was investigating a broadleaved wood, Newfield Plantation, across the road from the entrance to the reserve, where a footpath runs northwards along the eastern edge of the wood, adjacent to a collapsing ivy-covered limestone wall. Amazingly, Terry found a couple of V. pusilla at SE45362816 under twigs at the base of the wall (see the photograph). Eager to find out more about the species on the site, he returned the following Saturday and turned up a further four examples, three under fallen stones somewhat further along the wall. He spent the rest of that day searching other possible sites in the neighbourhood, but without success. On the 31st October 2013, Adrian, Terry and David Lindley revisited the site and tried to establish its distribution and how common it was. They found that it was in fact very common at the site, along the whole length of the wall from its beginning to around SE45392839, a distance of about 0.5km. This is a very significant record, the best site in Yorkshire.
Monitoring
The Fylingthorpe Slug is not native and therefore not formally of conservation concern, but it is hoped that it will persist at its current site. Happily, this is likely as the building is listed. Meanwhile, the Wall Whorl Snail is classified as ‘Least Concern’ and ‘Nationally Scarce’ under current IUCN classification (Seddon et al., 2014). Given the fact that the majority of its records are in VC69, the national assessment might understate its threat elsewhere. In Yorkshire, threats such as wall reconstruction (especially using cement), the spread of agriculture, and a warming climate could all be relevant. As the wall at Newfield Plantation is a boundary between arable fields to the east in North Yorkshire, and woodland to the west in Leeds, it might be vulnerable to repair.
About 20 species of non-marine molluscs in Yorkshire are candidates for monitoring at key sites every 5 to 10 years. There are now very few active conchologists in the County, and as they are of increasing age, regular monitoring is becoming more difficult. If you would like to join Adrian or Terry in the field, whatever your current experience, please get in touch!
Acknowledgements and further information
NEYEDC would like to thank Terry and Adrian for their time and expertise in helping to create this blog. They would also like to thank Marie Jeanne Perry for permission to use her original photograph If you’d be interested in contributing a piece for the series, contact Lucy at lucy.baldwin@neyedc.co.uk. To find out more about biological recording, see the Naturalists page on our website.
Crawford, T.J. (2012) Yorkshire Naturalists’ Union excursions in 2012. Fairburn Ings RSPB Reserve (VC64) 19 May 2012. Molluscs. The Naturalist 137: 226-227.
Kerney, M.P. (1976) Atlas of the non-marine Mollusca of the British Isles. Institute of Terrestrial Ecology, Cambridge.
Kerney, M..P. & Cameron, R.A.D. (1979) A field guide to the land snails of Britain and north-west Europe. Collins, London.
Lindley, D.J. (2016) Notes on Vertigo alpestris and Vertigo pusilla in Watsonian Yorkshire. The Naturalist 141: 27-38.
Rowson, B., Turner, J., Anderson, R. & Symondson,W.O.C. (2014a) Slugs of Britain and Ireland. Identification, understanding and control. AIDGAP, FSC Publications, National Museum of Wales.
Rowson, B., Anderson, R., Turner, J.A. and Symondson, W.O.C. (2014b) The slugs of Britain and Ireland: undetected and undescribed species increase a well-studied, economically important fauna by more than 20%: The Slugs of Britain and Ireland: Undetected and Undescribed Species Increase a Well-Studied, Economically Important Fauna by More Than 20% (plos.org)
Seddon, M.B., Killeen, I.J. & Fowles, A.P. (2014) A review of the non-marine Mollusca of Great Britain: Species Status No. 17. New Evidence Report No: 14, 84 pp, National Resources Wales, Bangor.
Welter-Schultes, F.W. (2012) European non-marine molluscs, a guide for species identification. Planet Poster Editions, Göttingen.