TEETH OF SMINTHUS.
In the remainder of the Muridæ, the molars, which are again only three in number on each side, are generally rootless, although occasionally the growth of the teeth stops and they close up below. The molars are composed of triangular prisms placed alternately. Two groups are thus characterised, namely, the Voles and the Zokors.
The VOLES (Arvicolinæ), which, next to the true Rats and Mice, form the most important group of Muridæ, are represented in the northern parts of both hemispheres. The brain-case in these animals is rhomboidal when looked at from above, the frontal region of the skull is much contracted, and the zygomatic arch stands out very far. The infra-orbital opening is as in the Murinæ. The molars are so constructed of alternating triangular prisms that the whole margin is enclosed by deep angular folds of enamel. These are mouse- and rat-like Rodents of a rather stout build, with the limbs and tail of moderate length, or short, and the latter more hairy than in the true Murines. The ears are short, often nearly concealed beneath the fur.
The true Voles (genus Arvicola) number about fifty known species, which have been arranged by various writers under a considerable number of sub-genera, generally corresponding to differences in mode of life. Three species, representing three of these groups, are found in Britain, and may serve to illustrate the natural history of the Voles. The largest of these is the well-known WATER VOLE, or Water Rat, as it is more commonly called (Arvicola amphibius), an animal rather smaller than the Common Rat, and having, like all the Voles, the muzzle considerably blunter, and the tail a good deal shorter and more hairy. Although thoroughly aquatic in its habits, the feet of the Water Vole are not webbed; they have five toes, but the thumb in the fore feet is very short. The general colour of the fur is reddish-brown, mixed with grey on the upper surface, and yellowish-grey beneath; the ears are nearly concealed in the fur; and the incisor teeth are deep yellow in front, and very strong, presenting a considerable resemblance to those of the Beaver, to which great Rodent the Voles were formerly considered to be related. It is very widely distributed, being found in all parts of Europe, and stretching right across Central and Northern Asia, to China, the Amoor region, and the Sea of Okhotsk. In Ireland, however, it is not found. Its habits vary a little in different localities, but in general it haunts the banks of rivers, in which it burrows to a considerable distance. In the water it is very active, swimming and diving with the greatest facility, and it is here that it seeks its food, which appears to consist exclusively of vegetable substances. Professor Bell says:—“A decided preference is shown, during the summer months, for the inner or concealed part of some species of sword-flags, which is very succulent and sweet-tasted. As this portion is usually below water, the animal gnaws the plant in two near its root, when it rises to the surface, and being conveyed to some sound footing, is consumed at leisure. In default of its more favourite food, it will make a satisfactory meal on the common duckweed. Only the green and fleshy leaf is eaten, the roots and other fibrous parts being rejected. While feeding on this plant, the creature sits like a Squirrel on its haunches near the water’s edge, and taking up a lump of the soft and slimy-looking mass in its fore paws, eats a small part only, and letting the remainder fall, takes up some more in the same manner.” The accusation sometimes brought against the Water Vole of eating worms and insects, and even of destroying fish-spawn, young fishes, and even young ducks, seems to be entirely unfounded. In the winter the Water Voles will feed on turnips, mangel-wurzel, and other roots, and also upon the bark of osiers and willows, to which they do considerable damage; and in some localities they appear to frequent gardens at all seasons of the year, burrowing in the ground, and feeding luxuriously upon the produce of the gardener’s labour. Their greatest activity is in the twilight, but in quiet situations they are to be seen abroad during the day. The female produces from two to six young at a litter: twice in the year in Britain, according to Professor Bell; three or four times in the course of the summer, according to Brehm and other Continental naturalists.
MOLAR TEETH OF THE WATER RAT.
A second British species is the FIELD VOLE, or Short-tailed Field Mouse (Arvicola agrestis), which is less than half the size of the Water Vole, and has the tail only about one-third the length of the body, instead of half that length. In the general form of the head and body the two species are a good deal alike, but the ears project farther beyond the fur in the Field Vole. The general colour of this species is greyish-brown, becoming tinged with reddish or yellowish on the sides; the lower surface is pale grey or dirty white, and the tail is brown above and greyish beneath. The Field Vole is a very abundant species in the northern and central parts of Europe, but is wanting in Ireland and south of the Alps and Pyrenees. It is usually found in damp places, especially in meadows in the neighbourhood of woods and copses, where it forms burrows of considerable extent. Its food consists almost exclusively of vegetable substances, such as roots and herbage, and in times of scarcity it will climb up trees and bushes to feed on the tender parts of the bark. In case of necessity, however, it does not disdain animal food, but will eat insects and meat, and even sometimes kill and devour smaller individuals of its own species. It breeds three or four times in the year, producing from four to six young at a birth, in a small round nest made of moss and leaves, among the roots of the herbage in some hollow of the ground. Their increase, which would otherwise be very formidable, is checked by the smaller predaceous beasts and birds, such as the Weasel, the Kestrel, and the Owls, which destroy them in great numbers. The BANK VOLE (Arvicola glareolus[53]), the third British species, which is chestnut-coloured, with white feet and with a longish tail, closely resembles the preceding species in its habits, but feeds rather on fruits and roots than on herbage, and is far more addicted to a diet of animal food, freely devouring insects, worms, snails, and even young birds and carrion. It is pretty generally distributed over Europe, but not so uniformly as the Field Vole, which it even exceeds in fecundity, the females producing from four to eight young three or four times in the year, in a nest constructed of grass and moss placed in a hollow of the surface of the ground among dense herbage.
SOUTHERN FIELD VOLE.