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THE -NATURALIST. 



exercise their vocation incessantly and where most requisite. The reproduc- 

 tive powers of birds and their wonderful instinct of migration are also due 

 to the nature of the office imposed upon them. When in the North the 

 insect world relapses into its wintry hybernation, and sleeps under layers of 

 deep snow, most of the bird tribe betake themselves to the warmer 

 latitudes of the south, there to continue the performance of the same duties ; 

 whilst those which remain all the year round in one place gather up the larvse, 

 the ova, the nests of insects^ the few flies or spiders which may be tempted 

 out of their hyemal recesses by some stray sunbeam, and the Coleoptera 

 which gnaw at the bark of trees. 



In these days it would almost appear as if the great and important 

 services rendered by birds were insufficient for the purpose ; for complaints 

 are heard from Germany and Switzerland that they are invaded by swarms of 

 those varieties of destructive insects which are habitually seen in small 

 numbers only. They lay waste green meadows, vegetable gardens, crops of 

 wheat or flax, fruit trees, and forests, and they torment alike animals and 

 men, take the inhabitants by surprise, and destroy their prospects. 



Among the destructive beetles we may mention the Aeantliopoda, the 

 Astynomus ceclili, the Antlionomus, Bostriclius typographus, which in 

 1780 and the following years destroyed more than a million of fir-trees in the 

 Hartz mountains, and in Switzerland, and more recently committed other 

 awful depredations ; and lastly, the HydroyMlus atei, a very dangerous 

 insect for preserved fish-ponds. — Several species of butterflies, otherwise sa 

 innocent, belong when in the larval state to the class of pernicious articulated 

 animals ; the principal of these are the Bomhyx processionea, the Plialena 

 hombyx, the Pieris, the Lasiocampa^ the Neustria, and the Tinea. As for the 

 other sorts of inferior insects, such as Gryllotalpa, the Aphis, the grasshop 

 per, the ant, different species of the gadfly, wasps, flies, worms, and snails, it 

 is almost needless to speak of them, they are but too well known as plagues. 

 The Acridium migratorium has already penetrated into Southern Switzerland 

 and we are forced to come to the conclusion that the number of destructive 

 insects in general is gradually augmenting on. the Continent. This arises 

 evidently from the diminution of insectivorous birds, which is in a precise 

 ratio to the increase of insects, and if we investigate the causes of this dimi- 

 nution we shall find more than one, both in this and other lands. Generally 

 speaking, the progrsssive cultivation of the soil is not very favourable to 

 animals living in a state of freedom. It has already driven the fallow deer 

 from the woods ; the elk, the lynx, the wolf, the bear, the ibex from the 



