DAMAGE CAUSED BY ANIMALS. 135 



betrayed by the bore-dust collecting at the entrance-hole, and by 

 the entrance-holes themselves, and the air-holes communicating 

 every now and again with the main gallery, which are apparent 

 without difficulty when the bark is not too rough and scaly. On 

 standing timber their presence is indicated by the exudation of 

 white drops of resin, as well as by the bore-dust, which, falling 

 clown from above, chances to get caught in the rough scales of 

 bark, and on cobwebs near the foot of the tree. When exit-holes 

 are numerous and irregularly distributed over the stem, this 

 plainly shows that the beetles have already begun to swarm, and 

 that annihilative and exterminative remedies are too late for 

 application in reference to these. 



As already remarked, most bark-beetles exhibit a decided pre- 

 ference for sickly crops of backward growth, and timber in which 

 the natural flow of resin has become stagnant ; hence by frequent 

 thinning and clearing of the woods from such material, by re- 

 moving all windfall stems and broken trees, and such as have 

 been prejudicially influenced in growth by wind, snow, ice, or 

 any other natural cause, by clearing the falls as soon as possible 

 of recently felled timber, by grubbing up the stumps of such trees, 

 and utilising their roots and branches, or if that cannot be done 

 by at any rate barking the stems felled, the best measures are 

 adopted for preventing the reproduction of these insect enemies 

 on any large scale. When the breeding-places naturally more 

 convenient to them are wanting, the beetles also attack sound 

 stems, and for the most part perish in consequence of the resinous 

 outflow that follows ; but when thousands of such small punctures 

 or wounds have been inflicted, the tree grows sickly (ivttts), 

 and then offers a normally suitable breeding-place for the remain- 

 ing beetles, as may only too often be seen when attacks of bark- 

 beetles take place to any calamitous extent. All such sylvi- 

 cultural operations as are recommendable against injuries of every 

 sort, against storms, ice and snow accumulations, stripping of the 

 bark by deer, c., are also distinctly favourable to the prevention 

 of serious attacks from bark-beetles, the chief protection against 

 which, as against injurious insects of all kinds, must undoubtedly 

 be looked for in the formation and reproduction of mixed woods 

 in place of pure forests ; for in the former, not only are the con- 

 ditions less favourable for the reproduction of insects, but there is 

 at the same time a greater abundance of insectivorous birds. 



