CHAPTER XXV 



INSECTS AND DISEASE 

 FLIES AND MOSQUITOES 



Vocabulary 



Excrement, waste matter thrown off by animals from the intestine 



or kidneys. 



Cooperation, working together for a single purpose. 

 Invariably, always, without exception. 

 Contract, to " take" a disease. 



Another insect order which we shall take up very briefly is the 

 diptera (two-winged) which includes the flies and mosquitoes. 

 They are studied chiefly because of their relation to the carrying 

 of disease germs. The diptera differ from all other insects by 

 having but one pair of wings, the posterior pair being replaced by 

 flat or knob shaped balancers. Their mouth parts are fitted for 

 piercing, rasping, and sucking, and their metamorphosis is complete. 



The Typhoid Fly. The common house fly (typhoid fly) has very 

 highly developed mouth parts adapted for rasping and sucking, 

 large eyes, and short fleshy antennae. Its wings, though but two 

 in number, are well developed, and operated at high speed by the 

 powerful muscles of the thorax; the posterior pair are replaced by 

 flattened balancers. The six legs are well developed and the feet 

 (tarsi) are provided with claws and sticky hairs which aid in loco- 

 motion. Unless these hair tips are very free from dust they will 

 not stick well and the fly cannot walk readily on smooth surfaces, 

 hence the care with which it cleans its feet by constantly rubbing 

 them against each other and its body. 



Life History. However, our principal concern is with the life 

 history and habits of the fly rather than with its structure, since 

 it is in this connection that it affects man's health. 



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