De land- en zoetwater mollusken van het 'Fort aan de Nekkerweg', de Beemster, Noord-Holland

During fieldwork carried out in autumn 2007 on the fortification 'Fort aan de Nekkerweg' in the Beemster, North-Holland, the presence of 36 species of land- and freshwater molluscs could be registerd. In spite of the fact that the fortification had not been in use for some 30 years three invasive slug species could be recorded: Milax nigricans, Tandonia sowerbyi and Boettgerilla pallens. Most of the fortification is covered with a dense and rather tall cover of several species of grass, which made sampling for the smaller species an almost impossible task. Reducing the vegetation by means of grazing sheep or by mowing (or a combination of both) may reveal without doubt some additional land snails.