THE COMMON GRASS MOUSE 449 
mice live together in pairs,’ or at all events have some sense of 
property in their nests. They have also some sense of sanita- 
tion, since they deposit their ordure in little heaps at particular 
places, as at the mouths of their burrows. The rest of their 
life-history is soon told. Although not incapable of climbing, 
and extremely agile without being fast, they never under 
normal circumstances leave the ground, and may be seen 
running, but not bounding or jumping, to and fro in their 
haunts, or sitting at little bare places at the mouths of their 
burrows, at almost any hour of the day ; and no doubt they are 
equally active at night. They probably spend their time 
alternately in short sleeps and meals, their light slumber 
guarding against surprise. They are quite capable of amassing 
stores of food for winter use, always of such provender as will 
keep, but for obvious reasons this propensity is not very highly 
developed in the comparatively mild climate of England. 
They are copious drinkers and their appetite is enormous, 
Dr Henry Laver having ascertained’ the weight of clover 
consumed by a single captive individual in one day to be six 
drachms (apothecary’s weight = 2.3 grammes). 
They are very attentive to their fur, cleaning it carefully 
after the manner of a cat. 
At intervals, either owing to favourable weather *— moist 
summers and mild winters resulting in exceptionally nourishing 
vegetation—but perhaps occurring independently in a natural 
cycle, the numbers of Grass Mice undergo a very exceptional 
increase, beginning gradually and extending over several years 
if unchecked. More litters, and those of abnormal size, make 
their appearance, and presently the usual equilibrium between 
mice and vegetation is upset, the grass is all consumed, the 
mice, usually in autumn, begin to stray into woods, bark * 
trees, cut their roots, otherwise cause damage, and people 
become aware that it is a “vole year” or that there is a 
“plague” of mice. With the increased numbers there ensues 
1 Adams has taken 73 males to 24 females, a proportion of, roughly, 3 males to 1 
female; but the figures, although suggestive, are too small to form the basis for a 
definite statement as to the relative numbers of the sexes. 
* Zoologist, 1881, 461. ® R. Service, Ann. Scott. Nat. Hist., 1892, 134. 
* Charles Oldham (Zoologist, 1890, 98) once observed them engaged in barking 
hollies. 
