VOLE, a book-name (invented by Dr J. Fleming, author of a work on British animals) for the water-rat and those species of field-mice which have cheek-teeth of the same general type. Although the British representatives of this group should undoubtedly retain their vernacular designations of water-rat and short-tailed field-mouse, the term “vole” is one of great convenience in zoology as a general one for all the members of the group. Systematically voles are classed in the mammalian order Rodentia, in which they constitute the typical section of the subfamily Microtinae in the Muridae, or mouse-group. As a group, voles are characterized by being more heavily built than rats and mice, and by their less brisk movements. They have very small eyes, blunt snouts, inconspicuous ears and short limbs and tails, in all of which points they are markedly contrasted with true rats and mice. In common with lemmings and other representatives of the Microtinae, voles are, however, broadly distinguished from typical rats and mice by the structure of their three pairs of molar teeth. These, as shown in the figure, are composed of a variable number of vertical triangular prisms, in contact with one another by two (or one) of their angles. On the number and relations of these prisms the voles, which form an exceedingly large group, ranging all over Europe and Asia north of (and inclusive of) the Himalaya, and North America, are divided into genera and subgenera. Examples of some of these are afforded by the English representatives of the group.
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| Upper and Lower Molars of the Water-Rat (or Water-Vole), Microtus amphibius. |
The first of these is the common short-tailed field-mouse, or “field-vole,” Microtus agrestis, which belongs to the typical section of the type genus, and is about the size of a mouse, with a short stumpy body, and a tail about one third the length of the head and body. The hind feet have six pads on their inferior surfaces, and the colour is dull grizzled brown above and greyish white below. The molar teeth have respectively 5, 5 and 6 prisms above, and 9, 5 and 3 below. This rodent is one of the commonest of British mammals, and frequents fields, woods and gardens in numbers, often doing considerable damage owing to its fondness for garden produce. It is spread over the whole of Great Britain (exclusive of the Orkneys), while on the continent of Europe its range extends from Finland to North Italy and from France and Spain to Russia.
The second and larger species is the water-rat, or “water-vole,” which belongs to a second section of the genus, and is commonly known as Microtus (Arvicola) amphibius, although some writers employ the inappropriate specific name terrestris. It is about the size of a rat, and has long soft thick fur, of a uniform grizzled brown, except when (as is not uncommon) it is black. The tail is about half the length of the head and body, and the hind feet are long and powerful, although not webbed, and have five rounded pads on their lower surfaces. In the upper jaw the first molar has 5, the second 4 and the third 4 prisms, of which the last is irregular and sometimes divided into two, making 5. In the lower jaw the first molar has 7 prisms, of which the 3 anterior are generally not fully separated from one another, the second 5 and the third 3. The water-rat is perhaps the most often seen of all English mammals, owing to its diurnal habits. It frequents rivers and streams, burrowing in the banks, and often causing considerable damage. Its food consists almost wholly of water-weeds, rushes and other vegetable substances, but it will also eat animal food on occasion, in the shape of insects, mice or young birds. The female has during the summer three or four litters, each of from two to seven young. The range of the water-rat extends over Europe and North Asia from England to China, but the species is not found in Ireland, where no member of the group is native.
The red-backed field-mouse or “bank-vole” may be distinguished externally from the first species by its more or less rusty or rufous-coloured back, its larger ears and its comparatively longer tail, which attains to about half the length of the head and body. On account of an important difference in the structure of its molars, it is now very generally referred to a distinct genus, under the name of Evotomys glareolus; these teeth developing roots at a certain stage of existence, instead of growing permanently. Their prisms number respectively 5 and 4 and 5 above, and 7, 3 and 3 below. The habits of this species are in every way similar to those of the one first on the list. Its range in Great Britain extends northwards to Morayshire, but it is represented in an island off the Pembroke coast by a distinct form; on the continent of Europe it extends from France and Italy to southern Russia, while it is represented in northern Asia and North America by closely allied species. Fossil voles from the Pliocene of England and Italy with molars which are rooted as soon as developed form the genus Mimomys. (R. L.*)