A survey for Geyer's Whorl Snail Vertigo geyeri was undertaken at Cors Erddreiniog Site of Special Scientific Interest (SSSI)/National Nature Reserve (NNR) and Cors Geirch SSSI/NNR in October 2016. The survey failed to locate the species at either site. Survey locations were selected on the basis of previous records from Cors Erddreiniog (1985-2007) and Cors Geirch (1996-2008).

The apparent loss of Vertigo geyeri from former strongholds at Cors Erddreiniog is likely to be attributable to changes in grazing management. In some areas, particularly Nant Isaf Spring Field (Compartment 13c), prolonged under-grazing has led to the development of dense tussocks of Black Bog-rush Schoenus nigricans and Blunt-flowered Rush Juncus subnodulosus, which have shaded out the open "Carex lawn" habitat required by the snail. This process is particularly evident in Nant Isaf Spring Field, which had not been grazed for more than twenty months prior to the survey. Elsewhere on the site, the loss of the species may be associated with over-grazing or periods of under-grazing followed by cattle poaching of the remaining open habitat.

Similar declines have occurred at Cors Geirch, where the development of a rank, tussocky sward resulting from insufficient grazing appears to have reduced or eliminated the lightly grazed Carex lawn habitat formerly occupied by the species. Voucher specimens collected in 2005 have been confirmed by the author of this report; however, no voucher specimens from the four individuals recorded in 2008 were available for examination.

As small populations of Vertigo geyeri can be easily overlooked, it would be premature to conclude that the species is extinct at either Cors Erddreiniog or Cors Geirch. In addition, several locations that previously supported very small populations were not surveyed in 2016 and should be revisited as a priority. More frequent monitoring is required to inform appropriate grazing management should remnant populations persist at either site. If the species is found to be surviving at low density, the development of simplified and cost-effective surveillance methods is recommended.

Even in the absence of confirmed records, it is essential that areas previously occupied by Vertigo geyeri continue to be managed appropriately. Grazing should be reinstated at Nant Isaf Spring Field as a matter of urgency, while current grazing pressure in Compartment 9 at Cors Erddreiniog should be reduced. At Cors Geirch, the area where the species was recorded in 1996, 1998 and 2005 has become excessively rank, and grazing levels should be increased to reopen seepage areas and improve sward structure, thereby restoring suitable habitat conditions.