324 PRINCIPLES OF ECONOMIC ENTOMOLOGY 



desired to control and cannot be considered as an efficient 

 practise for many insects that are troublesome on the 

 average farm. In this connection it may be stated that it 

 is good entomological practise to use wire fences in place 

 of the old rail or board fences, and it is a good plan to culti- 

 vate as close as possible to fence lines with the consequent 

 reduction of the growth of weeds, bushes, and so on. 



Another matter which deserves attention is a close guard- 

 ing against the introduction of pests in seed or along with 

 introduced plants, as many of the serious pests are readily 

 transferred from place to place in such materials as straw 

 and various kinds of seed packages and thus gain a foot- 

 hold in a locality in which they ha\e not been troublesome 

 before. 



NATURAL ENEMIES. 



Insects are preyed upon l)y many natural enemies — birds, 

 reptiles, toads, spiders, and these serve as checks to their 

 inordinate increase. Bird protection has been strongly 

 urged as an aid in insect control and certainly all or nearly 

 all of our common field birds are best allowed all the pro- 

 tection possible. Especially the small insectivorous birds 

 such as wrens, swallows, chickadees, titmice, etc., should be 

 given all the protection possible. Spiders are also generally 

 useful rather than injurious and should be undisturbed. 



PREDACEOUS AND PARASITIC INSECTS. 



The position of the ]:»redaceous and parasitic insects is one 

 of considerable complexity, since their attacks may be 

 directed against both injurious and beneficial forms, and 

 their relation to human interests depends, of course, upon 

 the nature of the insects which they attack. In a general 

 way the carnivorous species feed upon the herbivorous ones, 

 and the herbivorous ones being ordinarily the most destruc- 

 tive to valuable crops, the average result may be looked 

 upon as advantageous. The study of these natural enemies 

 of the injurious insects has formed a considerable part of 



