CHAPTER XXVI 

 OTHER BLOOD-SUCKING FLIES 



Importance. — Although the mosquitoes hold the center of 

 the stage as regards importance as human parasites, there are 

 many other members of the order Diptera which affect the wel- 

 fare of the human race. From a medical point of view the 

 Diptera are far more important than all other arthropods put 

 together. Besides the mosquitoes, which we have seen are the 

 transmitters of at least four and probably five diseases, two of 

 which are of prime importance, the Diptera include the Phle- 

 botomus flies, which are known to be the sole disseminators of 

 phlebotomus or three-day fever, and are believed to be the 

 transmitters of verruga in Peru and of oriental sore in North 

 Africa and possibly other places; the tsetse flies, which are 

 transmitters and intermediate hosts for the trypanosomes of 

 sleeping sickness; the stable-fly and other biting allies of the 

 housefly, which maj^ carry the bacteria of anthrax and other 

 diseases from dead or dying animals to human beings; the gad- 

 flies or horseflies, one species of which is incriminated as the 

 transmitter of the African loa worm, and all of which may act 

 in the same capacity as stable-flies, to transmit bacteria mechani- 

 cally from the blood of a diseased animal to a healthy animal 

 or person; and the blackflies (Simuliidse) and " no-see-ums " 

 (Chironomidse), which are sometimes terrible pests though not 

 known to be disease carriers. Besides these blood-sucking 

 species, the Diptera include also all the insects which live in the 

 human body as maggots, and also the housefly and allied species 

 which, though not properly to be considered parasites, are 

 nevertheless of incalculable importance as mechanical spreaders 

 of disease germs. 



General Structure of Diptera. — To understand the relations 

 of these numerous important insects and their classification, 

 we must make a brief survey of the characteristics and classi- 

 fication of the order Diptera. The whole order can usually be 



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