DAMAGE CAUSED BY ANIMALS. 119 



But a number of purely sylvicultural measures are also at our 

 disposal to prevent the recurrence of calamitous danger from in- 

 sects. It cannot be denied that the method, now usual in many 

 parts of Germany, of having extensive successive -annual clear 

 falls of timber, which leads to a series of large annual falls or 

 areas stocked with homogeneous pure forests of coniferous species 

 I of equal age, and altogether the more extensive cultivation of 

 i coniferous crops in comparison with broad-leaved species, has not 

 I inconsiderably increased the danger from insect enemies. More 

 I especially in young crops and plantations, weevils or rostral-beetles 

 (Curculionidae) are not only much more numerous, but also vastly 

 more destructive than formerly. The avoidance of large total 

 l clearances annually, so far as possible the reproduction or forma- 

 tion of mixed crops of various species of trees, which experience 

 has shown to be much less exposed than pure forests to injurious 

 attacks from insects, the proper sequence or location of the annual 

 falls so as to afford the woods as much protection as possible 

 against violent winds, the timely and regular carrying out of thin- 

 ning operations, in which sickly poles and stems are removed, the 

 abeyance of removal of leaf-mould, the want of which may affect 

 the productive capacity of the soil, and the careful conduct of all 

 cultural operations like sowing and planting in what appears 

 to be a promising manner, all tend, whether individually or com- 

 bined, to militate against the increase of destructive insects, and 

 i 'constitute the sylvicultural methods of obviating their attacks. 



61. Exterminative Measures in general. 



Annihilative measures must vary somewhat in each case 

 according to the habits of the insect concerned. From the life- 

 history of the latter it may be determined at what stage of de- 

 velopment the easiest point of attack may be found, should it be 

 possible to undertake destructive operations on a large scale for 

 its extermination. From the study of its habits may be learned 

 the best time for seeking it, whether at its work of destruction, 

 or after it has withdrawn into its hiding-places, or if it may be 

 advisable to offer it special material to feed upon, with a view to 

 inducing it to use this as its hiding-places or breeding-centres, or if, 

 finally, efforts ought to be made to entrap it on its way to the 

 feeding-places. But whilst, in the case of each individual species 

 of insect, the study of its peculiar habits and of its life-history 



