126 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



Although from the silk- worm we get all the silken cloth and 

 thread we use, and from the honey-bee all the honey and 

 beeswax, yet these are almost the only species of insects of all 

 the myriad living kinds that afford man useful products. 

 But in two other and far more important ways, insects are of 

 direct benefit to us. Some of them act as scavengers of con- 

 siderable importance, and many of them kill injurious species 

 of their own class. It is, indeed, on the many predaceous and 

 parasitic insects that we rely for chief protection from the 

 many injurious and dangerous kinds. We can, and do, 

 make much headway against injurious insects by the use 

 of artificial remedies, but without natural checks on their 

 increase, among which checks the attacks of other insect 

 species are the most important, insect pests would overrun us 

 completely. 



A knowledge of the special structure, physiology and mode of 

 development of insects is necessary as a basis for good work in 

 economic or applied entomology. And a knowledge of insect 

 classification, which of course is based on similarities and 

 dissimilarities both of structure and of development and habit, 

 and which indicates by a few words the existence of these 

 resemblances and differences, is also most important to the 

 economic entomologist. Hence our first consideration of 

 insects will concern itself with their structure, physiology, 

 development and classification. The study of the grasshop- 

 per, already made, has given us a good understanding of the 

 insect body. But there is much modification, or specialization, 

 of general body-shape and character as well as of the various 

 particular parts of it, as antennae, mouth -parts, legs, wings, 

 etc., and it will be advisable to examine in some detail the 

 external features of the body of a highly specialized insect 

 such as the honey-bee. A number of statements concerning 

 the general make-up of the insect body, already made in con- 

 nection with the study of the grasshopper, will be repeated and 

 expanded and a number of technical names of parts of the 

 body redefined. The grasshopper was studied primarily as 

 an introduction to the invertebrates in general. The bee will 

 be studied primarily as an introduction to the insects. 



