THE HOUSE FLY 



489 



PROBLEM IX. WHAT ARE OTHER DISEASE CARRIERS AND 

 WHAT DISEASES DO THEY CARRY? 



Demonstration 5. Observe the foot of a house fly under a com- 

 pound microscope. Why it is able to carry bacteria. 



Allow a fly to walk across a sterile agar plate. Cover the plate and 

 set it aside in a warm place for several days. Describe the plate. 



Demonstration 6. The life history of the typhoid fly. 



Expose pieces of raw beef where flies will light on them. After a 

 few hours, cover this meat in glass dishes or small battery jars with 

 screen covers. 



Watch the meat. In pieces on w T hich eggs were laid by the flies 

 describe the stages of development as they appear. Do the larvae 

 grow? They are called maggots. State how the pupae differ from 

 the larvae. Watch to see the adults emerge from the pupal case. 



How long does a complete life history take ? How many generations 

 of flies might develop during a hot summer? 



The house fly. We have already learned that mosquitoes of 

 different species carry malaria and yellow fever. Another addition 

 to the black list of disease-carriers is the house or typhoid fly. The 

 development of the 

 house fly is extremely 

 rapid. A female may 

 lay from one hundred 

 to two hundred eggs 

 at one time. These 

 are usually deposited 

 in filth or manure. 

 Dung heaps about 

 stables, outdoor toilets, 

 neglected garbage 

 cans, and fermenting 

 vegetable refuse form 

 the best breeding 

 places for flies. In 

 warm weather, the eggs 

 hatch a day or so after they are laid and the larvae or maggots 

 crawl out. After about one week of active feeding these wormlike 

 maggots become quiet and go into the pupal stage, whence under 

 favorable conditions they emerge within less than another week as 

 adult flies. The adults breed at once, and in a short summer 



1 





s 



mm ** "' ' ¥ mw% 



Paul Griswold Howes 



A blue-bottle fly depositing eggs in the bill of a dead starling, 

 which will furnish food for the young larvae. 



