Desmoulin's whorl snail  (Vertigo moulinsiana)

This tiny snail, not more than 3mm tall, is one most people are unlikely to encounter unless you have a stream flowing through your garden. The shell is a pale-yellow to reddish-brown in colour, translucent and very glossy. Desmoulin's whorl snail bears a very close resemblance to two other species. These snails are similar in size and an expert eye is required to tell them apart. The Desmoulin's has four tiny 'teeth' around the entrance to its shell - one of the others has six while the second species has none at all.

The snail is found over most of Europe, but nowhere is it a common species. It occurs in south and eastern England along a corridor, which runs from Cromer on the Norfolk coast to Studland in Dorset.

Desmoulin's whorl snail prefers humid conditions of the sort found around the edges of ponds, streams and rivers. It may also be found in swamps and fens, especially where the water table is close to ground level.

For most of the warmer parts of the year the snail lives on the leaves of tall wetland plants such as sedge and sweet reed-grass. When these die back in winter, the snails probably retreat to the leaf-litter to avoid frost. In spring, they return to their browsing of the algae and fungi growing on the upper leaves of the waterside plants. The snails can live for about a year and they lay eggs throughout the summer months. Both adult and young snails can be found together over most of the warmer parts of the year, but towards the autumn the adult snails die off.

Desmoulin's whorl snail has probably never been a common species, but damage to its habitat has restricted its populations largely to Sites of Special Scientific Interest (SSSIs).

This species is included in the UK Biodiversity Action Plans (UK BAP) and is also on English Nature's Species Recovery Programme. The results of a recent survey carried out by English Nature suggested that this snail might be more widespread than had been supposed. However, it is still considered to be a species at risk, and work to conserve it has concentrated on preserving its preferred habitat from the effects of agriculture, drainage and development schemes, and pollution.

The species' inclusion on Annex II of the European Habitats and Species Directive means that those areas where it occurs can be designated as Special Areas of Conservation (SACs). These SACs are eligible for money from the European LIFE fund for work on habitat management and restoration. Amongst the areas that have benefited from SAC designation are the Norfolk Broads and the Rivers Avon, Kennet and Lambourn Floodplain.