There is a group of tiny snails with some rare species that have strongholds in the Yorkshire Dales. Two of these are associated with limestone rock: The Mountain Whorl Snail (Vertigo alpestris) and the Wall Whorl Snail (Vertigo pusilla).
Both of these snails are very small (approximately 2mm long), cylindrically-shaped whorl snails that can be separated by the different direction that the shells of each species spiral.
The Mountain Whorl Snail coils in a ‘right-handed’ fashion. It is found on rock, scree, old drystone walls and lightly wooded rocky areas. The key area for this species is in Cumbria but there are important populations found in the Yorkshire Dales National Park and other areas of north east England, North Wales and Scotland.
Although the Wall Whorl Snail is a more widespread species, it is still uncommon with important populations present in the Yorkshire Dales National Park. This species is found in leaf litter on shaded areas of rock and drystone walls. It is ‘left-handed’ snail, as are most Whorl Snails.
Geyer’s Whorl Snail (Vertigo geyeri) is an endangered species that is associated with very wet, swampy places such as in springs and seepages, especially where the vegetation is low and dominated by fine grasses and sedges. It was very common for a time soon after the glaciers retreated at the end of the last ice age, but is now extremely rare owing to habitat loss. It is ‘left-handed’ and seldom exceeds 1.9 cm long.
Craven Door Snail
Craven Door Snail (Clausilia dubia) is restricted to the northern limestone areas of northern England and southern Scotland. Its range has contracted since the nineteenth century probably due to atmospheric pollution. The Craven Door Snail lives in crevices in rocks or in leaf litter. It emerges in moist conditions to feed on algae and lichen. A favourite habitat is ungrazed limestone pavements. Other species of Door Snail, such as the Two-toothed Door Snail (Clausilia bidentata) are common in Dales woodlands and can be encountered ascending tree trunks after a spell of rain.
Sandbowl Snail or ‘Sand Amber Snail’ (Catinella arenaria) occurs in only two locations in England, one of these being in the Orton and Crosby Gill areas of the National Park. It occurs in very similar habitats to Geyer’s Whorl Snail and the two have been found together at the same sites. Amber snails are so-called because they have somewhat amber-coloured shells which are often translucent so that the snail’s body can be seen inside.