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customed to certain locations ; and if, by any accident, a cer- 

 tain region happens to be deserted by them for a season, insects 

 of all kinds gain a start and destroy vegetation. 



" In the year 1198, the forests in Saxony and Brundenburg 

 were attacked with a general mortality. The greater part of 

 the trees, especially the Firs and the different kinds of Pine, 

 whose bitter and aromatic branches are rarely the prey of in- 

 sects, died, as if struck at the roots by some secret malady. It 

 was not here, as often happens, that the foliage above was de- 

 voured by caterpillars, the trees perished without showing any 

 signs of external disease. This calamity became so general, 

 that the Regency of Saxony sent natui'alists and sldlful forest- 

 ers to find out the cause. They soon found it in the multipli- 

 cation of one of the Lepidoptera insects, which in its larva 

 state, insinuated itself within the tree, and fed upon the wood. 

 Whenever any bough of the Fir or the Pine was broken, this 

 detestable insect was found within it, which had often hollowed 

 it out even to the bark. From the report of the natui'ahsts it 

 was made apparent, tliat the extraordinary increase of this insect 

 was owing to the entire disappearance of several species of Wood- 

 pecker and Titmouse, which had not for some years been seen 

 in the forest." 



Dr. Lettsom, an English physician, remarks that he was as- 

 sured by an intelligent farmer, that, notwithstanding the power 

 of severe firost to kill insects, they are always most numerous 

 after a cold winter, because the birds are prevented from find- 

 ing them by the hardness of the soil. When a hard frost binds 

 the surface of the ground it protects the dormant insects from 

 the birds no less than it exposes the insects to injury from the 

 cold. It would seem, therefore, that Natui'e, while providing 

 checks to the over-multiplication of insects, has carefully guard- 

 ed them fi-om extermination, by taking care that when they are 

 more than usually exposed to one agent of their destruction, 

 they shall at the same time be less exposed to another. 



Buffon relates the following anecdote of a certain species of 

 Grackle, resembling om* Crowblackbiird, which is so injudic- 

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