CHAPTER 27 



THE CLASS INSECTA 



Of the classes of Arthropods, the insects are the most diverse and 

 widespread. More than 700,000 species have been described and prob- 

 ably as many more remain undescribed. Members of the class have 

 invaded nearly all possible terrestrial habitats, with forms occurring 

 from the coldest regions of the world to the tropics. Species have 

 successfully occupied the desert environment as well as the moist rain 

 forests. Many species live in fresh waters, and some have evolved 

 special apparatuses to live beneath the surface. Although a few species 

 live on the surface of the ocean and a few others in the intertidal zone, 

 there has been no real development of marine forms. 



Economically this class contains some of the most important of the 

 invertebrates. Some forms such as the bees are indispensible in the 

 pollination of many fruits ; others are important in the control of pests. 

 The honey and wax of the bee are useful products throughout the 

 world ; the culture of the silkworm is an important industry in many 

 countries. In some areas grasshoppers and beetle larvae are actually 

 an article of food. In addition, it is always interesting to speculate upon 

 the number of people who are employed for the control and study of in- 

 sects. 



On the less desirable side, some insects are important parasites, 

 such as the bot fly whose larvae burrow through the hides of cattle. 

 Many mosquitoes are important vectors of diseases such as malaria and 

 filariasis. Bacterial infections may be spread by the common housefly. 

 The trypanosomes are carried by a fly in Africa and by a biting bug 

 in the New World. Many of man's cereal crops are attacked by a host 

 of dififerent insects. Other crops have other pests : the cotton boll 

 weevil, tomato worms, cabbage moths, etc. Textiles are often at- 

 tacked by various species of moth and beetle larvae. 



With the tremendous number of species, great diversity of form, 

 structure, physiology, and habit is found among the insects. Never- 



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