Still wondering why a number of Drymaeus species are being blue, I received a message from Carol Ramsay sharing this link http://bit.ly/mrfWZb about another blue snail she had found in the UK. She thought it might have absorbed copper from the soil.
I forwarded her message to two colleagues, Edi Gittenberger and Ton de Winter, who answered her that the species depicted was Oxychilus draparnaudi (Beck, 1837), which is known to be blue. Ton wrote “The soft parts of these snails are bluish-grey, and in some illumination this colour can appear as distinctly bleu. This has nothing to do the copper in the soil. The soft parts of land snails usually are pale, greyish or brownish, but can have bizarre colours, bright green of red, or purple, or even a combination of colours, especially in the tropics“. Today, we briefly discussed this issue over lunch, but in the end we were still wondering what is causing the colours in the snail bodies and what might be the evolutionary advantage of being blue (or whatever colour the snail may have).