« 400 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 hfe 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. 
“Tf 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- 
