PROTECTION AGAINST ANIMALS. 125 



are always to be found but not numerous ; others appear 

 seldom, but when they appear, they muster up danger- 

 ously great numbers ; some are slow in their movements 

 and walk only; others fly and cover very quickly largo 

 stretches of forests. 



From this it will be seen that a keen observation is 

 required to be able to employ at the right time, and in 

 the right place, the proper means to moderate the damages, 

 and to prevent the further spreading of insect-pests. 

 The most efficacious measure of obtaining these results 

 consists in sparing and even fostering the multiplication 

 of the natural enemies of the injurious insects. The 

 equilibrium between useful and obnoxious animals is 

 kept up in the animal kingdom by the production of 

 such animals as persecute the injurious ones. This law 

 is nowhere more obvious than with insects. There a 

 considerable number can be looked upon by their de- 

 struction of obnoxious insects as real benefactors to 

 mankind. 



It is further recommended as a preventive means from 

 insect ravages the removal of stumps, dry trees and 

 branches, cut wood and timber, and the peeling off 

 the bark from timber in case it cannot be shifted 

 from the forest, whereby the breeding-places of insects 

 are destroyed. The most effective means to sup- 

 press the insect-plague, especially in wild or natural 

 forests, is the introduction of a syttematic management, 

 of which the first step would be a correct and periodically 

 repeated thinning by which we in time obtain a thoroughly 

 sound and vigorous growth of trees and to such trees 

 obnoxious insects cannot do much harm. 



If the just mentioned means to prevent the spread of 

 injurious insects are observed, it is not difficult to get rid 

 of them completely. For this purpose the bark of trees 

 invaded by insects should be stripped off and burnt, 

 the dead trees should be cut, and unless removed, 



