TUE FLY 79 



filth or crawled over it to lay their eggs are permitted to walk 

 over food, they may leave germs on the food. In this way 

 germs of such intestinal diseases as diarrhasa, dysenterj', 

 typhoid, and cholera are disseminated, pro\'ided these diseases 

 are present in the neighborhood. 



When people are crowdetl together, as in army camps, and 

 insufficient care is exercised to keep flies from access to the food- 

 stuffs, the transportation of intestinal diseases is appalling and 

 the death rate enormous. This was sadly illustrated in some 

 of the army camps of our Spanish-American War. The l:)est 

 way to prevent dysentery is to prevent the larvte of flies from 

 developing in the filth of the camps, and secondarily the adult 

 flies must be prevented from coming in contact with our 

 bodies and our food. 



The larvfe of Diptera may be exterminated by treating their 

 breeding-places with insecticides, of which kerosene oil is one 

 of the best. The adults may be kept away by screening the 

 doors and windows. 



Although so very numerous, flies would be still greater pests 

 if it were not for the fact that they are preyed upon by various 

 parasitic animals and plants. The larva of the house-fly 

 is sometimes infested by minute parasites belonging to the 

 insect group of Hymenoptera. A still more important foe is 

 a minute fungus which infests house-flies in the autumn. The 

 dead flies may often be seen on window-panes witli fine white 

 threads sticking out of the body, and surrounded by a halo 

 made up of the spores discharged from the fungus upon the 

 glass. Finally, robber-flies and spiders kill great numbers. 



The order Diptera is a large one and a difficult one to studjr, 

 for it contains many species frequently- composed of small indi- 

 viduals which are comparatively unknown. The members of 



