OTHER ENEMIES OF MAN 



223 



is the resting stage of an insect between the larva and 

 the adult stage. About four days later the adult fly 

 emerges from the pupa. The adult female is ready to 

 lay eggs about two weeks after she emerges from the 

 pupa. Thus in a little more than three weeks another 

 generation of flies may be started. 



How can we protect ourselves from flies? The most 

 important method of controlling flies is to prevent 

 them from breeding. If there were no breeding places, 

 there would be no flies. Horse manure should be kept 

 in covered containers or be treated with some sub- 

 stance that kills fly maggots. Chloride of lime may 

 be used for this purpose. Garbage, slops, and refuse 

 of all sorts should be kept in covered containers and 

 destroyed at least once a week. Open toilets and 

 cesspools should not be tolerated. 



FIG. 352. STAGES OF DEVELOPMENT OF HOUSE FLY 



(The egg is considerably magnified.) 



Fly traps and fly poisons may also be used in com- 

 bating flies. However, these methods are not so effec- 

 tive as the ones previously mentioned. Formaldehyde 

 solution made by dissolving two teaspoonfuls of for- 

 malin in a pint of a mixture of milk and water is an 

 effective fly poison. If this poison is used it must be 

 kept away from small children. 



Flies also have many natural enemies. Certain birds 

 and insects destroy many flies. Frogs, toads, and liz- 

 ards eat them for food, and the house centipede is a 

 deadly enemy of flies. Many flies also die a natural 

 death. A number of the more vigorous ones crawl into 

 cracks and crevices and hibernate during the winter 

 months. Most of the flies that appear in early spring, 

 however, have spent the winter in the pupa stage. 



Do you think that all flies could eventually be de- 

 stroyed if we applied the scientific knowledge that we 

 have? What is your community doing to combat flies? 



What is the life history of mosquitoes? There are 

 many varieties of mosquitoes, but fortunately only a 

 few carry disease germs. In temperate climates but 

 two common varieties are found. One of the two va- 

 rieties is called Culc.r (ku'leks). The common house 

 mosquitoes belong to this group. They are annoying 

 and a nuisance, but they are comparatively harmless. 



The other form is called Anopheles (a-n6f'e-lez). This 

 type transmits the malarial fever germ. In tropic re- 

 gions a mosquito called Aedes carries the germ which 

 causes yellow fever. See Figure 353, which shows the 

 life history. Notice the differences in each stage of 

 development. 

 The germ causing malaria is a tiny one-celled ani- 



(Aedes) 

 common mosquito yellow-fever mosquito 



FIG. 353. LIFE HISTORY OF MOSQUITOES 



mal that lives in the blood stream of the victim. The 

 mosquito Anopheles penetrates the skin of a human 

 being who is suffering from malaria and sucks up 

 blood containing the malaria germs. The germs live 

 in the body of the mosquito. When the mosquito bites 

 another person, it leaves some of the malaria germs in 

 the wound. These germs may then increase in number 

 and cause malarial sickness in the second person. 



Losses due to malaria are very great. In the United 

 States several million cases of this disease occur each 

 year. Although it is seldom fatal, it reduces greatly 

 the working capacity of its victims. This results in a 

 loss of millions of dollars to our nation each year. 

 Malaria also lessens one's resistance to other diseases. 



How can we control mosquitoes? Mosquitoes could 

 be eliminated entirely by preventing them from breed- 

 ing. Mosquitoes lay their eggs on stagnant water. In 

 about three days the eggs hatch into larvae known as 



