o/Hj/lobius Abietis in Fir Plantations. 445 



barked indiscriminately; and also that this mischief appeared 

 always to be effected in the same manner, that is, " by devouring 

 the bark of the young plants all round, from the ground to the 

 height of about six inches, and in many instances by gnawing the 

 root itself through and through." 



Among the variety of curious facts stated in his Lordship's let- 

 ter, scarcely any can be so interesting to the Naturalist as the 

 temporary nature, or periodical appearance of these Plagues. We 

 can easily conceive that when a forest abounds with an extraordi- 

 nary number of Mice, they must, like hares and other glirine 

 animals, in the absence of other food, resort to the bark of very 

 young trees ; but the difficulty is to comprehend the cause of these 

 swarms being periodical. Many causes may indeed be imagined 

 as tending to promote their increase ; but, on perusing the above 

 letter, I do not think that any one can be reckoned as absolutely 

 certain, or sufficient to account for the evil. A few years a^o, the 

 neighbourhood of Strasburg was, without any assignable cause, or 

 at least without any cause sufficient to account for their numbers, 

 infested in like manner by swarms of Mice, and the only means 

 that seemed to answer towards their extirpation were the pits so 

 much recommended by Lord Glenbervie. It would appear, how- 

 ever, that the ravages occasioned by Mice in plantations are con- 

 fined to the young trees ; so that in their taste, at least, these ani- 

 mals differ entirely from the greater part of decorticating insects, 

 which usually prefer trees of great size and age. Lord Glenbervie, 

 for instance, says, that Mice do not attempt to bark or eat the 

 roots of those trees, of which the stems have acquired a diameter of 

 two or more inches ; and Mr. Harvey states, that when an extraor- 

 dinary quantity of Mice made their appearance in Lord Bagot's 

 woods, they were not observed to gnaw the bark off, which he 

 accounts for by the circumstance of there being no young planta- 

 tions there. 



Giving, however, all due credit to the valuable details of Lord 

 Glenbervie, and, convinced as I am with him, that the injury done 

 to the young plantations in the Royal forests, was effected by 

 Mice, I would warn the Inspectors of woods and forests that no 

 opinion can be so erroneous, or so hurtful to the trees under their 



Vol. I. 2 p 



