The land snails and slugs of the northern Yorkshire Dales: an Australian’s perspective

In 2005 I made an extended visit to the United Kingdom and Ireland from my home in Australia, including several months living in the village of Barningham, in Teesdale in the northern Yorkshire Dales. Mary Seddon (Cardiff) put me in touch with Leeds conchologist Adrian Norris, who provided a friendly introduction to the land snails of the area. Adrian is currently working towards a one kilometre square coverage of Yorkshire land snails, and arrangement was made that I would contribute with some field survey work in the northern Yorkshire Dales, an area which had hitherto received little attention. The following short paper summarises the findings of this work and compares the Yorkshire land snail fauna with that found in Australia.

Northern Yorkshire Dales

Ten 1 km square sites in the northern Yorkshire Dales (9 sites in Teesdale and 1 in nearby Swaledale) were surveyed for land snails and slugs in March-May 2005. The study area was on limestone geology and sites sampled ranged from farmland (5 sites) to broadleaf woodland (3 sites), village garden (1 site) and heather moorland (1 site). Survey methods comprised hand searches along old drystone walls and hedgerows, lifting and replacing ground debris such as fallen timber and loose rocks, hand-raking leaf litter and examination of tree trunks and herbage. Sampling effort varied, with some sites sampled at only a single location while others were sampled at a number of locations across the square.

A total of 47 species from 17 families were recorded (see Table 1), representing about a third of the UK land snail fauna (Kerney 1999). The greatest contributors to this diversity were the Helicidae (8 species), Zonitidae (7 species) and Arionidae (7 species). Average species richness per site was 19 species, with the highest recorded diversity (30 species) in woodland and the lowest (7 species) in moorland. The village site at Barningham was notable in that 20 species (all except Cepaea hortensis) were found in one small cottage garden (Dove Cottage NZ082103).

Several indicator species for ancient woodland were recorded in this study, such as Azeca goodalli, Limax cinereoniger, and to a lesser extent Columella edentula, Cochlodina laminata and Perforatella subrufescens. The woodland site in Hening Wood near Scargill, where the river Greta passes through a deep wooded gorge, was the most significant woodland site sampled, with the highest overall species diversity including four of the above five species.

This study also provided further demonstration of the importance of old drystone walls and hedgerows as secondary refugia for land snails in British farmland. Thirty four species (72% of the total recorded) were found in these microhabitats, with noteworthy records including Pyramidula rupestris, Clausilia dubia, Balea perversa and Ashfordia granulata. The farmland site at Greta Bridge (which included the outer wall of the old parkland of Rokeby Park), had the third highest recorded species diversity (24 species), including three of the above four species.

Comparison with Australia

Whereas the modern UK land snail fauna dates from only the end of the last glacial period (less than 15 000 years ago), that of Australia has an unbroken history of many millions of years (Bishop 1981). The Australian native land snail fauna comprises an estimated several thousand species in 25 families (Stanisic 1994; Stanisic and Ponder 2004). The most speciose families are the Charopidae, Camaenidae and Helicarionidae (Stanisic 1994). Most Australian species occur in moister coastal and subcoastal areas, but some are found in semi-arid and arid habitats of the interior. About 90% of species occur in rainforest (Stanisic 1994), which today covers only about 1% of the continent. It is estimated that about two thirds of the Australian land snail species have not yet been formally described (Stanisic and Ponder 2004), with many areas poorly sampled or not sampled at all. Even in the well-settled Sydney area, about a third of the 80 or so native species known await formal description (Clark 2004). The majority of research in Australia to date has focused on resolving taxonomy, and field studies involving living animals (eg Murphy 2002) are extremely rare.

Land snail species richness in Australia ranges from 5 or less species per site (a site defined as 1 km2 or less) in dry eucalypt forest to 20-30 species per site on limestone outcrops and up to 40 or more species per site in rainforest (Stanisic 1994; Clark 2004). Upland rainforest and limestone outcrops in particular have high numbers of narrow range endemics (Stanisic 1994). In contrast the UK land snail fauna has no endemic species and, apart from a few late glacial specialists with relictual distributions, most native species are generally broadly distributed (Kerney 1999).

Changes to the wooded landscape of the UK through human activity over the last 6000 years resulted in a mosaic of new habitats which have acquired their own characteristic land snail assemblages (Kerney 1999). Landscape changes in Australia as a result of 60 000 years or more of Aboriginal human presence are not clearly known (being confounded by major global climatic change over that period), but 200 years of European occupation and development have seen rapid and drastic changes to the landscape. In some regions of southeastern Australia, for example, 80% or more of the pre-1770 vegetation has been cleared. The Australian native land snail fauna has not had time to adjust to these sudden and severe changes. Most native species in urban and agricultural landscapes are now restricted to remnants of the original vegetation, and are thus comparable to woodland-dependent species in the UK. The different style of farming in Australia is another factor in the general paucity of native land snails in agricultural habitats. In contrast to the UK, where old hedgerows and stone walls in farmland provide important habitat for many species (Kerney 1999), fields in Australian agricultural areas are typically bordered by wire-strand fences, with minimal microhabitat value for land snails.

The distinction between native and introduced land snails in the UK is blurred, partly because some introductions date back to the Neolithic (Kerney 1999), and partly because so many species, both native and introduced, utilise human-modified landscapes. Most of the 60 or so land snail species introduced to Australia over the last 200 years are found in agricultural, urban and disturbed habitats (Ponder 1997). Many originate from the UK and Europe, generally widespread ecologically catholic species typical of gardens and waste ground such as Cochlicopa lubrica, Oxychilus alliarius, Limax maximus, Deroceras reticulatum, Cernuella virgata, Theba pisana and Helix aspersa (Kerney and Cameron 1979; Kerney 1999). Populations of some native Australian land snail species can survive in quite small remnants of native vegetation in urban and agricultural landscapes (Clark 2004). Virtually nothing is known concerning the interactions between introduced and native land snail taxa in Australia (Ponder 1997), but it can be expected that these interactions will eventually result in characteristic land snail assemblages for Australian urban and agricultural landscapes.

Conclusion

“Travel broadens the mind” they say, and I certainly found that my time in Yorkshire broadened my appreciation of land snail ecology. Solem (1984) noted that there were few locations in the world in which land snail diversity exceeds 30 species. The species richness found at some sites in the northern Yorkshire Dales was comparable to that occurring in Australian diversity hotspots such as rainforest and limestone areas. Considering the 10 surveyed sites as a whole, the northern Yorkshire Dales has a high land snail diversity within a relatively small area. The land snail fauna is also interesting in how it reflects the history of the area, with species ranging from those which are disturbance sensitive and dependent on remnants of ancient woodland to others reliant on habitats created and sustained by human activity.

Acknowledgements

Adrian Norris (Leeds) and Winston Ponder (Sydney) provided helpful comments on earlier drafts of this paper. Adrian also provided me with a copy of Kerney and Cameron (1979), helped with identification of specimens collected and suggested the topic for this paper. My children Sam, Jess and Nicola enjoyed helping with field surveys. Thanks also to Sheila Caton and Jon Smith for their hospitality during our stay in Barningham.

References

Bishop, M.J. 1981. The biogeography and evolution of Australian land snails. Pp. 925-954 in Ecological Biogeography of Australia, edited by A. Keast. Dr W. Junk Publishers: The Hague.

Clark, S.A. 2004. Native snails in an urban environment – conservation from the ground up. Pp 78-81 in Urban Wildlife: more than meets the eye, edited by D. Lunney and S. Burgin. Royal Zoological Society of New South Wales: Mosman, NSW, Australia.

Kerney, M. 1999. Atlas of the Land and Freshwater Molluscs of Britain and Ireland. Harley Books: Colchester, England.

Kerney, M and Cameron, R.A.D. 1979. A Field Guide to the Land Snails of Britain and North-west Europe. W. Collins and Co Ltd: Glasgow.

Murphy, M.J. 2002. Observations of the behaviour of the Australian land snail Hedleyella falconeri (Gray, 1834) (Pulmonata: Caryodidae) using the spooland- line tracking technique. Molluscan Research 22: 149-164.

Ponder, W.F. 1997. Conservation status, threats and habitat requirements of Australian terrestrial and freshwater mollusca. Memoirs of the Museum of Victoria 56(2): 421-430.

Solem, A. 1984. A world model of land snail diversity and abundance. Pp. 6-22 in World-wide snails. Biogeographical studies on non-marine Mollusca, edited by A. Solem and A.C. Van Bruggen. E.J. Brill/Dr W. Backhuys:Leiden.

Stanisic, J. 1994. The distribution and patterns of species diversity of land snails in eastern Australia. Memoirs of the Queensland Museum 36(1): 207-214.

Stanisic, J. and Ponder, W.F. 2004. Forest snails in eastern Australia – one aspect of the other 99%. Pp. 127-149 in Conservation of Australia’s Forest Fauna (second edition), edited by D. Lunney. Royal Zoological Society of New South Wales: Mosman, NSW, Australia.

Figure 1. (Fig 5, page 14) Limax cinereoniger (underside view showing diagnostic sole pattern). This large slug is considered a good indicator of ancient woodland, and was found in the wooded gorge of the Greta River near Scargill.

Figure 2. (Fig 6, page 14) Arianta arbustorum (23 mm) Cepaea hortensis (20 mm), Cepaea nemoralis (25 mm) and Helix aspersa (40 mm) are the largest land snails in the northern Yorkshire Dales and among the largest species in the UK, but are dwarfed by the eastern Australian rainforest species Hedleyella falconeri (Caryodidae) (100 mm).