The bank vole (Myodes glareolus; formerly Clethrionomys glareolus) is a small vole with red-brown fur and some grey patches, with a tail about half as long as its body. A rodent, it lives in woodland areas and is around 100 millimetres (3.9 in) in length. The bank vole is found in western Europe and northern Asia. It is native to Great Britain but not to Ireland, where it has been accidentally introduced, and has now colonised much of the south and southwest.
The bank vole lives in woodland, hedgerows and other dense vegetation such as bracken and bramble. Its underground chamber is lined with moss, feathers and vegetable fibre and contains a store of food. It can live for eighteen months to two years and is mostly herbivorous, eating buds, bark, seeds, leaves and fruits and occasionally insects and other small invertebrates. It readily climbs into scrub and low branches of trees. It breeds in shallow burrows, the female rearing about four litters of pups during the summer.
The bank vole is a small rodent resembling a mouse but with a stouter body, a slightly rounder head with smaller ears and eyes and a shorter, hairy tail. The dorsal surface is reddish-brown, with a greyish undercoat and the flanks are grey with a reddish-brown sheen. The underparts are whitish-grey sometimes tinged with dull yellow. The ears are larger than those of most voles. The adult head and body length varies between 3.25 and 4.75 inches (83 and 121 mm) and the tail ranges from 1.5 to 3 inches (38 to 76 mm). The weight is between 15.4 and 36 grams (0.54 and 1.27 oz). Young animals are darker in colour with greyer underparts. The bank vole is capable of making growling sounds and can utter low-pitched squeaks.
In areas such as Great Britain, where the only other small vole is the short-tailed vole (Microtus agrestis), the bank vole is distinguished by its more prominent ears, chestnut-brown fur and longer tail. The northern red-backed vole (Myodes rutilus) from northern Scandinavia and Russia, has a shorter tail and is paler with less grey in its pelage. The grey red-backed vole (Myodes rufocanus) from northern Eurasia, is larger with a distinctive reddish back.
The bank vole has a palearctic distribution. It is native to Europe, Asia Minor and parts of Western Siberia. It does not occur in Iceland, Ireland or northern Scandinavia (except for Finland) and is absent from the Iberian Peninsula and most of Italy. It was introduced into south western Ireland in the 1950s where it has taken hold and there are fears that it may be displacing the native wood mouse (Apodemus sylvaticus). A subspecies found on the island of Skomer in West Wales, the Skomer vole (Myodes glareolus skomerensis), is much larger than the mainland bank vole and there may be 20,000 individuals on the island in late summer.
The bank vole is found in forests, especially in deciduous and mixed woodland with scrub, low plants and leaf litter. It is also present in hedgerows, field verges, among bracken and brambles, river banks, swamps and parks. In mountainous regions and the northern part of its range it occurs in coniferous woodland at altitudes of up to 1,800 metres (5,900 ft). It is not found on bare soil and ample ground cover seems a necessity.
In the Mediterranean region, at the southern extent of its range, it is a habitat specialist and is found in moist woodland but not in grassland and bushy places. At the fringes of forested areas it is possible for there to be a metapopulation consisting of a number of spatially separated populations of bank vole that come and go according to the season and local events. Some areas may be devoid of voles during the winter and be repopulated during the summer only to become empty of voles again in October. The further from permanently inhabited forest the location is, the fewer females there are and the more widely does the number of individuals fluctuate.
The bank vole is active by day and also at night and it does not hibernate in winter. It excavates long, shallow branching burrows with multiple exits, sometimes tunelling along beneath the leaf litter. It gathers and stores food underground and makes a nest with moss, dry grasses and leaves close to the surface or even above ground. It is in general quite bold but is also very alert to the cries of other animals such as tits warning of aerial predators.
The bank vole is primarily a herbivore. Its diet varies with the season but usually consists of leaves, grasses, roots, buds, bark, fruits, nuts, grain and seeds. When feeding on grass stalks it may clip the stalks and lay the cut pieces in piles. Some food is carried back to the burrow where it is kept in dedicated storage chambers. It sometimes eats animal food in the form of insects, spiders and worms and may take eggs from the nests of birds nesting on the ground.
The bank vole climbs well and in the winter it feeds on the bark of trees including beeches, maples and larch up to several metres above the ground. It also eats tree seedlings and reduces the natural regeneration of woodland and when present in large numbers, is considered a forest pest. However, its harmfulness is relatively low in a healthy ecosystem because significant damage only occurs when numbers build up, and because it has a large number of natural enemies its population is normally kept under control.