1016 Desmoulin's whorl snail Vertigo moulinsiana
Description and ecological characteristics
Desmoulin’s whorl snail Vertigo moulinsiana is the largest Vertigo species, with a shell height up to about 2.6 mm. It is restricted to calcareous wetlands, usually bordering lakes or rivers, or in fens. High humidity appears to be important in determining local distribution within sites. It normally lives on reed-grasses and sedges, such as reed sweet-grass Glyceria maxima and tussocks of greater pond-sedge Carex riparia and lesser pond-sedge C. acutiformis, where it feeds on the microflora, and in autumn it may ascend taller reeds and scrub. Like all Annex II Vertigo species, it is highly dependent on maintenance of existing local hydrological conditions.
The species was more widespread during the early post-glacial period, but climatic change and destruction of its habitats for agriculture caused a contraction in its range.
European status and distribution
In Europe Vertigo moulinsiana is widely distributed north to Denmark and the extreme south of Sweden. There are few recent records, and it is regarded as rare in all range states. Within the EU, only England and Ireland are considered to support reasonable populations (Drake 1999), despite being close to the northern limit of the species’ range.
UK status and distribution
Recent surveys in England have indicated that Vertigo moulinsiana is not as rare as previously thought. It occurs at scattered sites in a band across southern England from Norfolk to Dorset, with isolated populations elsewhere (Drake 1999). Southern chalk streams have been shown to be as important as the East Anglian fens as strongholds for this species.
Site selection rationale
Sites have been selected to represent the strongholds of Vertigo moulinsiana in southern England and East Anglia, with additional outliers in Kent and north Wales. The selected sites represent the largest populations and also a range of ecological conditions, incorporating variation in river catchment type as well as representation of the species’ occurrence in wetlands. It is abundant in some patches at certain localities, and clusters of these patches of greatest abundance have been included in site selection.
Corsydd Llŷn/ Lleyn Fens
West Wales and The Valleys
The population of Desmoulin’s whorl snail Vertigo moulinsiana on Cors Geirch NNR occurs in stands of great-fen sedge Cladium mariscus in calcareous fen and is the only locality known for the species in Wales.
Kennet and Lambourn Floodplain
Berkshire, Buckinghamshire and Oxfordshire, Gloucestershire, Wiltshire and Bristol/Bath area
The cluster of sites selected in the Kennet and Lambourn valleys supports one of the most extensive known populations of Desmoulin’s whorl snail Vertigo moulinsiana in the UK and is one of two sites representing the species in the south-western part of its range in the important chalk stream habitat. Integrity of the population is being maintained by taking measures, including habitat creation, to safeguard populations. The habitat occupied at this site differs from the Fenland sites in East Anglia in that it is predominantly reed sweet-grass Glyceria maxima swamp or tall sedges at the river margins, in ditches and in depressions in wet meadows.
Norfolk Valley Fens
Norfolk Valley Fens is one of several sites representing Desmoulin’s whorl snail Vertigo moulinsiana in East Anglia. Within Norfolk Valley Fens there are a number of marginal fens around pingos – pools that formed in hollows left when large blocks of ice melted at the end of the last Ice Age. These are very ancient wetlands and several support strong populations of V. moulinsiana as part of a rich assemblage of Red Data Book and Nationally Scarce species in standing water habitat.
Dorset and Somerset, Gloucestershire, Wiltshire and Bristol/Bath area, Hampshire and Isle of Wight
There is an extensive population of Desmoulin’s whorl snail Vertigo moulinsiana along about 20 km of the margins and associated wetlands of the Rivers Avon, Bourne and Wylye. This is one of two sites representing the species in the south-western part of its range, in chalk stream habitat. It occurs here in a separate catchment from the Kennet and Lambourn, within an environment more heavily dominated by arable agriculture.
A sizeable population of Desmoulin’s whorl snail Vertigo moulinsiana lives beside ditches within pasture on the floodplain of the River Stour, where reed sweet-grass Glyceria maxima, large sedges Carex spp. and sometimes common reed Phragmites australis dominate the vegetation. Stodmarsh is a south-eastern outlier of the main swathe of sites and is important in confirming the role of underlying base-rich rock (chalk) as a factor determining this species’ distribution.
The Broads is the main stronghold of Desmoulin’s whorl snail Vertigo moulinsiana in East Anglia and is one of several sites selected in this part of its range. Several large populations are known, associated with standing and flowing water and ditch systems. This is a very important area for its wetland invertebrate fauna, and many Red Data Book and Nationally Scarce species occur here.
Waveney and Little Ouse Valley Fens
This site is one of several representing Desmoulin’s whorl snail Vertigo moulinsiana in East Anglia. At Weston Fen populations of this snail occur in a valley fen.
SACs where this Annex II species is a qualifying feature, but not a primary reason for site selection
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.