CHAPTER XIV
THE FIELD-MOUSE (Apodemus sylvaticus)
TO A FIELD-MOUSE
On turning Her up in Her Nest with the Plough, November 1785.
Another member of the Muridae, the field-mouse (Apodemus sylvaticus), is almost as great a nuisance in the trenches as the rat. The field-mouse is very like the house-mouse, with some of its features seen under a lens. The hind feet and ears and eyes are larger than are those of the house-mouse. Perhaps its much longer hind legs help most easily to differentiate the two species. The tail is of about the same length as the body and head added together, and is annulated, presenting some 150 rings. The hands have five-palmar pads, and the feet six pads. There are six mammae in the female, the anterior pair being pectoral.
The general colour of the dorsal surface is described as wood-brown, which pales at the front end and towards the shoulders and flanks, and grows to a more reddish tinge at the posterior end. The whole of the lower surface is of dull, white, silvery colour, and on some well-developed specimens there is a spot of buff, or orange, on the throat, which sometimes lengthens out to form a collar. Moulting seems to be rare—at any rate but a few cases have been recorded.
The field-mouse occurs all over Europe, and extends into parts of Asia. It is found all the way from Iceland, southward to Algiers, and from Ireland to India. In the Himalayas it has been taken at a height of 11,500 feet, and in the mountains of Europe it frequently occurs at a height of 7000 feet. It is certainly the most universally distributed of European animals, and the number of individual specimens probably far exceeds that of any other mammal which occurs in its district.
The field-mouse does not hibernate like the dor-mouse, but is active and hardy at all seasons of the year. Although, like other Muridae, it is probably vegetarian by ancestry, it is, in effect, quite omnivorous. It causes considerable loss in cornfields and gardens, especially to early-sown peas; it eagerly eats dandelions and any kind of grain or nut, or berry, or fruit, or bulb, or bud. Even fungi have been found in their winter stores; and one family was discovered which had eaten considerable quantities of putty with apparently no deleterious effect. Their fondness for bulbs is a great nuisance to the Dutch tulip-merchants. As many as 300 have been trapped in a fortnight in a single crocus-bed. They are also a nuisance to bee-keepers, inasmuch as they enter the hive and eat the honeycomb, especially during the winter. Whilst feeding in the hedgerows, or undergrowth, they frequently establish themselves in birds’ nests, and occasionally such nests become their permanent home.
They are not above sucking the birds’ eggs, or even devouring the young birds. They will sometimes enter disused tunnels and devour hibernating flies and other insects. Unlike rats, they seldom enter human habitations, and they are quite innocent of the peculiar odour which is so disagreeable in the house-mouse; and unlike the house-mouse and the harvest-mouse they are seldom found in stacks of corn. Their preference for berries explains the fact that they generally haunt woods and hedgerows, and their passion for growing corn accounts for the fact that they swarm in cornfields towards harvest-time.
The field-mouse, however, does not neglect open and barren districts, and is found from the sea-beach to the mountain-tops. It seems to flourish equally well in the flower-beds of the London parks and on the lonely hills of Scotland. Its activities are largely confined to the night-time, which may account for the exceptional size of its eyes. It is described ‘as bounding along in a peculiar zig-zag and erratic manner, remotely resembling the movements of a kangaroo or jerboa.’ Its spoor is very characteristic. The hind feet pressing nearly on the same spot as the fore feet, but less lightly than the latter. From time to time it sits upright, pricking its ears; and obviously its sense of hearing is very acute, for it distinguishes sounds inaudible to the human ear. It is mild in manner, gentle and inoffensive, extremely timid, and most easily trapped. It is to some extent gregarious, as many as fourteen or fifteen sometimes being found in the same burrow.
As Fig. 49 shows, the burrow generally has an entrance which is marked by a little heap of excavated earth. This leads down into the nest where food is often stored.
At the other end of the nest there are generally a couple of bolt-holes separated from one another by an angle of nearly ninety degrees.
The field-mouse is prolific, the female producing several litters throughout the greater part of the year. The mother carries the young-born litter about for two or three weeks, nipping the skin of her offspring at the side, half-way between the fore and hind legs. The average number of young born at one time is probably somewhere about five, though litters of nine are by no means unknown. All predaceous animals naturally eat field-mice, and they are the favourite food—at any rate, in some localities—of owls.