Rhön Spring Snail

The Rhön Spring Snail (Bythinella compressa) is only about 2 mm of size. It is an endemic species, only found in a small area shared by the states of Hesse, Bavaria and Thuringia. As indicated by the name, the Rhön Spring Snail inhabits springs and the following spring brooks, cold and unpolluted spring water are its essential requirements. Its most typical habitat are spring brooks of the alder marsh forests. Formerly, the Rhön Spring Snail was found in the open landscape as well, nowadays, it is almost exclusively restricted to larger tracts of deciduous forests. The Rhön Spring Snail is an important indicator species, due to its high habitat requirements.

The Rhön Spring Snail has a clear preference for springs above 450 m a.s.l. The majority of the populations are in basaltic areas, but there are also many populations known in sandstone or shell limestone. Most of the records are from seepage springs, which are permanently running or permanently wet. Noteable is the low occurence in captured springs. This indicates, that the Rhön Spring Snail is very sensitive towards human disturbances of their spring habitat. The Rhön Spring Snail prefers undisturbed forest springs, outside of this habitat, occurence and population size are rapidely declining. Their optimum seems to be temperatures between 5.5 and 8.5 °C, ph values around 7 ( i.e. Neutral) and a permanent low electrical conductivity – a measurement for the concentration of salts.

The distribution of the Rhön Spring Snail covers the whole area of the Hohe Rhön, parts of the Vorder- und Kuppenrhön and the Hoher Vogelsberg. In the Fulda-Haune Tafelland, Unterer Vogelsberg and the Sandsteinspessart, a few relicts are known. These form a northern and southern bridge between the two main distribution areas.

In 2010, the Hesse Federation for Cave and Karst Research (Landesverband für Höhlen- und Karstforschung e.V.) prepared an overall expertise on the situation of the Rhön Spring Snail in the Hesse State (Gutachten zur gesamthessischen Situation der Rhön-Quellschnecke [ ]) for the State authorities (Hessen-Forst FENA Naturschutz).