The Bank Vole (Myodes glareolus, formerly Clethrionomys glareolus) is a small rodent, 9 – 11 cm in length that can be recognised by its reddish-brown coat and short (4 – 6 cm) tail (Sterry, 2004 Collins Complete Guide to Irish Wildlife p. 20). Found in scrub, deciduous woods and hedgerows, it is active at both day and night in short burst when it often climbs amongst bushes. It is omnivorous, eating a wide variety of plant material as well as some insects (Chinery, 1987 Field Guide to the Wildlife of Britain and Europe p. 36).
A cosmopolitan European species, M. glareolus is found from Ireland through Europe to Lake Baikal in Siberia and from northern Turkey and Kazakhstan to inside the Arctic circle (Henbrot and Krasnov, 2005 An Atlas of the Geographic Distribution of the Arvicoline Rodents of the World). However its presence in Ireland is relatively recent. It was first discovered by A. J. M. Claassens in 1964 (Claassens and O'Gorman, 1965 Nature 205 pp. 923-924) in Listowel, Co. Kerry. Since then it has spread to the whole of Co. Limerick, Co. Kerry (except parts of the mountainous peninsulas), part of east Co. Tipperary, south-east Co. Clare and Co. Cork with the exception of the south-east (Smal and Fairley, 1984 Mammal Review 14 pp. 71–78). Mitochondrial DNA analysis of 81 bank voles by Ryan et al. (1996, Acta Theriologica 41 pp. 45-50) from 6 localities indicated that the founder population was small.
Its presence in Ireland is something of an anomaly: most alien species are introduced via the large ports on the east coast and radiate from there. So why is M. glareolus only found in the south-west? The answer may lie in the import of equipment for a hydroelectric scheme on the River Shannon from Germany in the 1920s. Stuart et al. (2007, Irish Naturalists Journal 28) compared mitochondrial DNA from M. glareolus individuals in Ireland and Germany and showed a close relationship between them which suggests that the German origin hypothesis may indeed hold water.