It is found chiefly in the South of England, becoming less abundant as we go north. In Scotland it is very scarce, and it does not occur in Ireland. It is more generally distributed on the Continent, where it ranges from Northern Italy to Russia and Siberia. The usual habitats of the Harvest Mouse are pastures and cornfields, where it climbs the stems of the tall grasses and corn plants, cutting off the ripe ears and carrying them to the ground where it picks out the grain. During the summer it feeds largely upon insects, caught in the same situations. At the same season it stores up much grain in burrows for use in the winter between its periods of sleep. Sometimes, however, instead of wintering in burrows in the earth, it tunnels into hayricks, and if undisturbed may even bring up a litter or two in the rick; as a rule it constructs the wonderful nursery which has won human admiration ever since White made the species known.
This is a ball-shaped nest about three inches in diameter formed of neatly plaited and woven blades of wheat or grass, with no definite opening, the grass blades being merely pushed aside to make entrance or exits where required, and closing again by their own elasticity. There is just sufficient room inside for the mother-mouse and her blind and naked offspring, whether they number four, eight, or even nine. This nest is suspended at some little distance—about half a foot—above the ground, several stems being incorporated in its walls to give it stability, or it may be lodged between the stem and leaf of a thistle, or a knapweed, in blackthorn bushes or broom. The bed is made of split leaves of corn or grass. The nests are not always so tough as that described by White, which "was so compact and well-filled that it would roll across the table without being discomposed, though it contained eight young." Several litters are produced throughout the year, varying in the number of young from five to nine; and one might expect that the species would be represented by individuals as numerous as those of the House Mouse. It must be remembered, however, that the diurnal habits of the Harvest Mouse and its methods of feeding expose it to the attacks of the larger birds; whilst the smaller carnivorous beasts do not neglect it. When the corn is cut the Harvest Mouse is often carried in the sheaves to the barn; in that case it spends the winter there, and does not go to sleep. It is considered that the modern reaping machine has caused a great reduction in its numbers.
Until about December the young of the year resemble the House Mouse in colour, and may easily be mistaken for it; then from the hind quarters forwards they begin to assume the redder tint. As the adult Harvest Mouse weighs only about a sixth of an ounce, it is not surprising that it should be able to sit on an ear of corn to which its capable little hands and prehensile tail have enabled it to climb with ease. But the familiar name must not delude us into supposing that it is only found in or about cornfields. It is also a denizen of the tall, rank herbage along ditches and untrimmed hedgerows. In winter it is frequently found about the lower parts of wheat and oat stacks.
Where the Harvest Mouse occurs it may be watched at close range by the quiet observer. Though as a rule timid and gentle in demeanour, it becomes at times savage and cannibalistic. It lacks the offensive odour of the House Mouse. Its voice is of a low chirping character, and has been likened to that of the wren.
With a more intimate knowledge of the structure of the various species of Mice, it has been found necessary to break up the old Linnean genus Mus into several smaller genera. In this process our little Harvest Mouse becomes the sole British representative of the genus Micromys.
Wood Mouse (Apodemus sylvaticus, Linn.).
An alternative name for the Wood Mouse is Long-tailed Field Mouse, and but for the fact that Linnæus dubbed it Mus sylvaticus, it would be better to adopt Pennant's designation, for it is much more an inhabitant of the field, the hedgerow, and the garden than of the wood. It is, indeed, the cause of something approaching despair to the keeper of the kitchen garden; for this is the miscreant that ploughs up and eats the newly sown peas that have not been rolled in red lead or soaked in paraffin. He has also a great fondness for strawberries at the moment they have become ripe.
The Wood Mouse is about three and a half inches long from the long snout to the base of the tail; and the tail by itself falls only a very little short of that length. The fur on the upper parts is a dark yellow-brown; the under parts white. In adults the line of demarcation is always distinct. There is a spot of buff or orange on the chest whose development in certain local races has enabled recent systematists to make five species out of this one. It has large and prominent dark eyes—for it is chiefly of nocturnal habits—and its long oval ears have the inner margin turned inwards at the base. The tail is dark brown above, and whitish below. It is the commonest of the British mammals in country places, but less frequent in Ireland. It is common in Europe as far north as Sweden and Norway.
As a rule it constructs its burrows underground or under the roots of trees, and here it stores up great quantities of nuts, haws, grain, and smaller seeds for use in winter, when it becomes inactive, though it does not really hibernate. But if there is a house handy to which it can gain entrance in late autumn, it prefers to become the guest of those whose garden has been a boon to it through the spring and summer. We have had them spend the winter cosily in our rolled-up tennis nets, stowed away in a shed to keep them dry in the off-season; and as potatoes were stored in the same place they consumed a number of these. On several other occasions Wood Mice were detected attempting impudently to enter the dwelling house by the back door. Once an entire family—mater, pater, and five active youngsters—succeeded in this enterprise; but they left incriminating evidence of their presence, though they were suspected of being ordinary House Mice. Accordingly a break-back trap, baited with cheese, was set one evening, and within half an hour its loud clap proclaimed its effectiveness. This trap appeared to show that the Wood Mouse is a simple-minded, unsuspecting creature, for it was reset with the same uneaten bit of cheese-rind for bait again and again, and no sooner was the trapper's back turned than another member of the family was secured. Seven times it sprang, and then its inaction appeared to be due to the fact that there were no more possible victims, for we saw no further traces of the mice. Its general resemblance to the House Mouse frequently leads to its being mistaken for that species.