Desmoulin's Whorl Snail Vertigo moulinsiana (Dupuy) in Essex
Results
River Cam
No Vertigo specimens were found at any point throughout this site. The majority of molluscs
(which were generally sparsely distributed) were Succinea/Oxyloma species.
Rushy Mead
No Vertigo specimens were recorded at this site.
Thorley Flood Pound SSSI
The following species were recorded: V. antivertigo, V. moulinsiana, V. pygmaea and Columella
edentula (from the willow woodland sedge beds). V. moulinsiana, was seen in moderate numbers in
the centre of the site, in habitat conditions that would appear to suit its micro-climate requirements
i.e. dense, tall sedge marsh with a water table that remains very close to the ground surface. To the
north, the marsh was deemed to be less suitable and this was confirmed by the lack of records from
here. At the southern extremity the sedge bed is more broken up, less dense and again appears to be
less suitable for the snail.
Little Hallingbury Marsh SSSI
The following species were recorded: V antivertigo, V. moulinsiana and V. pygmaea. V. moulinsiana
was seen sparsely across the centre of the site where the vegetation is perhaps at its most dense and
species-rich. The wetter southern units tended to have a greater abundance of Horsetail and this
more open structure may produce less favourable micro-climate conditions.
Sawbridgeworth Marsh SSSI
The following species were recorded: V. antivertigo and V. moulinsiana. Here, V. moulinsiana is
the most abundant Vertigo species present, with V. antivertigo only seen at one sample point closer
to the river. It was hardest to find in a unit that had been recently cut.
Parndon Mill
V. moulinsiana was the only species of Vertigo recorded during this study. This is a new locality for
this species and only the second significant site for Vertigo moulinsiana in the modern county of
Essex. The species was at its most obvious in two relatively low-lying sedge beds close to the
navigation channel. In these places it was more numerous than at any of the other survey sites in
the whole study, although even here it was nowhere near as dense as some studies have indicated is
possible (up to 600 per square metre, Killeen 2003).
Discussion
The River Cam site was, to some extent, the "long-shot" survey location, it being within a different
catchment to the other known sites and towards the headwater of the river, where water level
fluctuations might be more extreme. That said, V. moulinsiana has been found within the Cam
catchment, further to the north near Grantchester in Cambridgeshire (Killeen 2003) and so it was
not impossible that it might be found further up the catchment.
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Essex Naturalist (New Series) 21 (2004)