PART II. THE CLASSES OF INSECTS 



CHAPTER VI 



THE CLASSIFICATION OF INSECTS 



Identity of insects. If a crop of potatoes is being destroyed by 

 the Colorado potato beetle, it is at once recognized as the cause 

 of the injury, and the method of control is known or may be ascer- 

 tained from books or bulletins. In many cases, however, insects 

 are found abundant upon a crop which is evidently being injured, 

 but the casual observer may not be able to determine just which 

 are responsible for the injury without devoting more time to the 

 matter than is available, or without more knowledge of the habits 

 of insects than he possesses. Thus, when a colony of plant-lice is 

 found ruining a crop, there are usually found with them various in- 

 sects which are either preying upon them, as do the ladybird beetles, 

 aphis-lions, and syrphus-fly larvae, or caring for them, as do the ants. 

 No one would consider the ants as producing the aphides, but it is 

 not at all uncommon for those unacquainted with the life history of 

 plant-lice to assert that they are produced by the ladybird beetles 

 or other insects which are found associated with them, which are 

 consequently destroyed when they should be protected. If the insect 

 is very evidently the cause of the injury, but of unknown iden- 

 tity, it is of the utmost importance to identify it, so that its habits 

 and the best means of control may be ascertained. A knowledge of 

 the different kinds of insects is thus seen to be not only a matter 

 of theoretical or biological knowledge, but of considerable practical 

 importance. 



The classification of insects and the manner in which they may 

 be identified may be illustrated by a study of the ladybird beetles 

 already mentioned. Upon examining a ladybird beetle, we at once 

 recognize it as a beetle from the hard wing-covers, with the mem- 

 branous hind-wings folded beneath them, and the biting mouth-parts. 



6? 



