CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 27 



As might be inferred from a consideration of the immense number 

 of insects, the part they play in the economy of nature is an exceed- 

 ingly important one. Whether this part is to be considered a bene- 

 ficial or an injurious one when judged from the human standpoint 

 would be an exceedingly difficult question to determine. For if 

 insects were to be removed from the earth the whole face of nature 

 would be changed. 



While the removal of insects from the earth would eliminate many 

 pests that prey on vegetation, would relieve many animals of annoying 

 parasites, and would remove some of the most terrible diseases to 

 which our race is subject, it would result in the destruction of many 



groups of animals that depend, either 

 directly or indirectly, upon insects for food, 

 and the destruction of many flowering 

 plants that depend upon insects for the 

 fertilization of their blossoms. Truly this 

 world would speedily become a very differ- 

 ent one if insects were exterminated. 



It may seem idle to consider what 

 would be the result of the total destruction 

 of insects; but it is not wholly so. A care- 

 ful study of this question will do much 

 to open our eyes to an appreciation of the 

 wonderful "web of life" of which we are a 

 part. 



Most adult insects can be readily dis- 

 tinguished from other arthropods by the 



Fig- 37- Wasp with head, 

 thorax, and abdomen 

 separated. 



form of the body, the segments being grouped into three distinct 

 regions, head, thorax, and abdomen (Fig. 37). by the possession of 

 only three pairs of legs, and in most cases by the presence of wings. 



The head bears a single pair of 

 antennae, the organs of sight, and the 

 mouth-parts. To the thorax, are 

 articulated the organs of locomotion, 

 the legs and the wings when they are 

 present. The abdomen is usually 

 without organs of locomotion but 

 frequently bears other appendages at 

 the caudal end. 



These characteristics are also possessed by the immature form 

 of several of the orders of insects; although with these the wings are 



Fig. 38. Nymph of the red- 

 legged locust. 



