108 GENERAL ZOOLOGY 



A female may also eat plant juices, but requires a meal of 

 blood before she can ripen her eggs. 



Among important mosquito-borne diseases are malaria, 

 yellow fever, filaria, and dengue fever. Malaria is caused 

 by parasitic animals (Plasmodium) which live in the red 

 blood corpuscles of man and in mosquitoes. It will be 

 considered in detail in Chapter XII; it suffices to say here 

 that it is carried only by mosquitoes of the family Ano- 

 phelince. Man can get malarial fever only through the bite 

 of such a mosquito. The genus Stegomyia is the sole car- 

 rier of yellow fever. Filaria is a parasite worm (page 187), 

 causing the horrible disease known as elephantiasis, in 

 which parts of the body become enormously enlarged. 

 This malady is also inoculated hypodermically into the 

 bodies of unsuspecting persons by certain mosquitoes while 

 sucking the blood. The commonest mosquito in the United 

 States, Culex, carries bird malaria but does not transmit 

 any human diseases. 



The best way to treat mosquito-borne diseases is by 

 preventive measures i.e., better not to have the disease 

 than to try to get \yell after it has been acquired. This 

 means fighting mosquitoes, and in warm countries where 

 such diseases are prevalent, every intelligently managed 

 economic project has a staff of men who devote their whole 

 time to general sanitation. The building of the Panama 

 Canal depended as much upon the efficient work of doctors 

 and zoologists as it did upon the efforts of engineers, steam 

 shovels, and laborers. Mosquito larvse are eliminated from 

 particular districts by putting oil on the water; by intro- 

 ducing natural enemies of the larvse, such as sticklebacks, 

 top-minnows,, and other fish; and by the elimination of 

 breeding places (filling in or draining swamps, covering 

 reservoirs, etc.). The adults are kept from houses by 

 fumigation, screening, locally applied " dopes," etc. 



The midges (Chironomidce) are of great economic impor- 

 tance, chiefly because they occur in such numbers as to 

 furnish an easily obtained food for many animals. The 



