Little whirlpool ram’s-horn snail Anisus vorticulus
This tiny freshwater snail is both a national and international rarity found at Suffolk Wildlife Trust’s reserve at Carlton Marshes - an important UK site for this species. With a shell diameter of only 3.5 -6mm it’s devilishly difficult to spot and identify as it looks similar to the very common Whirlpool Ram’s-horn snail. It’s very exacting requirements means that the snail is only found on grazing marshes in well-vegetated open ditches fed by clean, slightly calcareous water. Over the last 60 years land use changes have had a major impact on the distribution of this little animal. Over-frequent mechanised ditch clearance and the conversion of grazing marshes to arable farming, together with the associated lowering of water tables and enrichment of ditch waters by artificial fertilisers, have all taken their toll. As a consequence UK populations have been reduced to a handful of places where conditions remain suitable. The Waveney Valley is one such site where some pockets of good habitat support strong populations. To ensure this rare snail continues to thrive, the ditches at Carlton Marshes are managed in a particular way which also favours many other rare aquatic invertebrates, including dragonflies. The ditches are only cleaned out when necessary, and then only in small sections, so that the snails can recolonize cleared sections from the uncleared stretches. Other Trust reserves in the area, such as Castle Marshes, also support this species. Continuing work with neighbouring landowners involves creating and restoring suitable habitat for these rare little snails. 43