72 USEFUL BIRDS. 
destruction of these insects may have been due in part to 
the hard winter that ensued, but the effect produced by the 
birds was most obvious. ‘ 
Such instances of the quelling of insect outbreaks by birds 
are noticeable, but the regulative influence steadily and 
perennially exerted by them, which tends to keep hundreds 
of species of injurious insects below the point where their 
injury to trees and plants would become apparent, is very 
seldom appreciated. . 
THE INCREASE OF INJURIOUS INSECTS FOLLOWING 
THE DESTRUCTION OF BIRDS. 
Many cases have been noted where the destruction of birds 
has been followed by an immediate increase in the numbers 
of injurious insects. Frederick the Great, king of Prussia, 
being particularly fond of cherries, was annoyed to see that 
the Sparrows were destroying his favorite fruit. An edict 
was issued ordering Sparrow extermination. All the re- 
sources of the fowler were brought to bear, and the cam- 
paign was so successful that not only were the Sparrows 
destroyed, but many other birds were either killed or driven 
away by the extraordinary measures taken against the Spar- 
rows. Within two years cherries and most other fruits were 
wanting. The trees were defoliated by caterpillars and other 
insects, and the great Frederick, seeing his error, imported 
Sparrows at considerable expense to take the place of the 
birds that had been killed. 
In the year 1798 the forests in Saxony and Brandenburg 
were attacked by a general mortality. The greater part of 
the trees, especially the firs and pines, died as if ‘struck at 
the roots by some secret malady. The foliage was not de- 
voured by caterpillars; the trees perished without showing 
any signs of external disease. This calamity became so gen- 
eral that the regency of Saxony sent naturalists and skillful 
foresters to find out the cause. They soon found it in the 
multiplication of one of the lepidopterous insects, which in 
its larval state fed within the tree upon the wood. When- 
1 Agricultural Value of Birds, by E. A. Samuels. Annual Report of the Mas- 
sachusetts State Board of Agriculture, 1865-66, pp. 116, 117. 
