The Land Snails and Slugs of Oxfordshire
Many species of snail and slug have precise habitat requirements and tend to be poor colonists of new sites. Thus, characteristic groups of 'indicator species' can occur in ancient woodland, undisturbed wetlands or calcareous grassland. Snails and slugs therefore make and important group for habitat and site assessment and are one of the best known invertebrate groups within the county.
Conservation Value
Ash-black Slug (Limax cinereoniger) - a characteristic but elusive slug of ancient Chiltern woodlands
Recording in Oxfordshire
Snails and slugs were very popular with Victorian 'shell-collectors' and most of Oxfordshire's rarities were well known to 19th century recorders. Early recording was patchy, reflecting the location of active collectors, and many areas remained badly under-recorded until the 1980's. During the 1980's and 1990's John Campbell (OBRC), Dr A.I. Spriggs and Steve Gregory (Northmoor Trust) adopted a more systematic approach to recording in order to achieve a more even coverage across the county. All habitats were sampled, both semi-natural sites, such as woodland, wetland and grassland, and man-made habitats such as churchyards. We wanted a genuine picture of the current status and distribution of all snails and slugs across the county.
Current Status and Distribution of Snails and Slugs within Oxfordshire
This recent intensive survey work has added 11 species (5 snails and 6 slugs) to the county list, which now stands at a very respectable 91 species. Over 20,000 species records are held on the OBRC database. We now have a much better understanding of the status and distribution of the county's fauna, especially of the more local species. The work cuminated in 2000 with the publication of the County Tetrad Atlas and a paper reviewing the changes in the status and distribution of Oxfordshire's species during the last century.
Perhaps the most encouraging finding was that many uncommon species associated ancient woodland (eg Mountain Bulin, Ena montana) or undisturbed wetlands (eg Desmoulins' Whorl Snail, Vertigo moulinsiana) have maintained their known ranges across the county. Unfortunately, snails associated with calcareous grassland have not fared so well. Two species in particular, the Lapidary Snail (Helicigona lapidicola) and the Heath Snail (Helicella itala), have shown rapid declines in recent decades. The former, once described as 'common on the Chilterns' is now known from just two sites in the county. Other species are recent colonists of the county and have considerably increased in abundance in recent decades. A good example is the Worm Slug (Boettgerilla pallens), unknown in the 1970's, but now widely found in gardens and churchyards.
