How Insects Cause or Carry Disease 43 



Coleoptera, containing the beetles; the Lepidop- 

 tera, containing the butterflies and moths ; the Hy- 

 menoptera containing the bees, ants and wasps, 

 etc. Four or five of these orders will be of more or 

 less interest to us. 



The order Diptera, or two-winged flies, is the 

 most important because to this belong the mos- 

 quitoes which transmit malaria and yellow fever, 

 and the house-fly that has come into prominence 

 since it has been found to be such an important 

 factor in the distribution of typhoid and other 

 diseases. 



FLIES 



The order Diptera is divided into sixty or more 

 families, many of which contain species of con- 

 siderable economic importance. For our present 

 consideration the flies may be divided into two 

 groups or sections: those with their mouth-parts 

 fitted for piercing such as the mosquito and horse- 

 fly, and those with sucking mouth-parts such as the 

 house-fly, blow-fly and others. 



Some of the species belonging to the first group 

 are among the most troublesome pests not only of 

 man but of our domestic animals as well. Next 

 to the mosquitoes the horse-flies (Fig. 22) are per- 

 haps the best known of these. There are several 

 species known under various names, such as gad- 



