4 ENTOMOLOGY 



natural checks upon its career are about to lend their powerful 

 aid to its suppression. We may even, for lack of this knowl- 

 edge, destroy our best friends under the supposition that they 

 are the authors of the mischief which they are really exerting 

 themselves to prevent. In addition to this knowledge of the 

 relations of our farm pests to what we may call the natural 

 conditions of their life, we must know how our own artificial 

 farming operations affect them, which of our methods of cul- 

 ture stimulate their increase, and which, if any, may help to 

 keep it down. And we must also learn where strictly artifi- 

 cial measures can be used to advantage to destroy them. 



" For the life histories of insects, close, accurate and con- 

 tinuous observation is of course necessary; and each species 

 studied must be followed not only through its periods of de- 

 structive abundance, when it attracts general attention, but 

 through its times of scarcity as well, and season after season, 

 and year after year. 



" The observations thus made must of course be collected, 

 collated and most cautiously generalized, with constant refer- 

 ence to the conditions under which they were made. No part 

 of the work requires more care than this. 



" This work becomes still more difficult and intricate when 

 we pass from the simple life histories of insects to a study of 

 the natural checks upon their increase. Here hundreds and 

 even thousands of dissections of insectivorous birds and pre- 

 daceous insects are necessary, and a careful microscopic study 

 of their food, followed by summaries and tables of the prin- 

 cipal results, a tedious and laborious undertaking, a specialty 

 in itself, requiring its special methods and its special knowl- 

 edge of the structures of insects and plants, since these must 

 be recognized in fragments, while the ordinary student sees 

 them only entire. 



" If we would understand the relations of season and 

 weather to the abundance of injurious insects, we are led up 

 to the science of meteorology; and if we undertake to master 

 the obscure subject of their diseases, especially those of epi- 



