224 



LIFE ON THE EARTH 



"wrigglers." The larvae remain in the water feeding 

 on the green scum on the surface. In about two weeks 

 the larvae change to pupae, and about four days later 

 the adults emerge from the pupae. 



Since mosquitoes need stagnant water on which to 

 lay their eggs, we can eliminate mosquitoes if we get 

 rid of stagnant water or keep it covered. This is a 

 difficult task requiring the cooperation of all. Swamp 

 areas must be drained or filled with dirt. Water re- 



Keystone-Undcrwood 



FIG. 354. POURING OIL OVER A POOL OF WATER TO 

 KILL MOSQUITO LARVAE 



ceptacles such as buckets, tin cans, rain barrels, and 

 cisterns must be kept covered. Where it is not possible 

 to remove all stagnant water, other methods may be 

 used to prevent mosquitoes from breeding. Pouring 

 kerosene on water kills the wrigglers because the film 

 of oil that forms on the surface prevents them from 

 getting air. Recently Paris green has been used suc- 

 cessfully to kill mosquito larvae. Powdered Paris 

 green mixed with dust (one part of Paris green to 100 

 parts of road dust) is thrown into the air so that the 

 dust cloud will settle over the body of water being 

 treated. In large swamp areas, the dusting is done 

 from airplanes. 



Mosquitoes have many natural enemies. Frogs, 

 toads, dragonflies, spiders, bats, and night-flying 

 birds devour them in large numbers. Countless mil- 

 lions of the larvae and pupae are eaten by fish and 



other insect-eating animals. Sometimes fish are intro- 

 duced into bodies of water to keep down the number 

 of mosquitoes. The enemies of mosquitoes reduce 

 their number, but do not prevent them from becoming 

 a pest. The elimination of the mosquito depends upon 

 cooperation of the citizens of each community. Are 

 you bothered with mosquitoes in your locality? If so, 

 it would be an interesting class project to survey your 

 community to locate the breeding places of these mos- 

 quitoes. 



In addition to house flies and mosquitoes certain 

 other insects such as blood-sucking flies, lice, fleas, 

 bedbugs, and roaches are known or believed to trans- 

 mit diseases. Many of these insects live in filthy places 

 and carry large numbers of disease germs on their 

 bodies. Infantile paralysis and bubonic plague are 

 sometimes transmitted to people by bedbugsrand fleas. 

 Typhoid fever and tuberculosis germs may be carried 

 about by cockroaches. Sleeping sickness germs are 

 transmitted by certain blood-sucking flies. 



Why is the rat often spoken of as the "n'ational 

 pest"? It is one of the most destructive animals in 

 the world. It has been estimated that more than 

 $200,000,000 worth of produce and property are de- 

 stroyed in the United States each year by rats. They 

 eat the standing grain in the fields, the stored grain, 

 and food in homes and stores. They kill small domes- 

 ticated animals such as growing ducks and chickens. 

 They gnaw holes in buildings <and weaken the" foun- 

 dations with their burrows. 



Of still greater importance is the fact that rats 

 carry disease germs. Rats carry bacteria that cause 

 the dreaded bubonic plague. This is primarily a dis- 

 ease of rats and other rodents. The disease is trans- 

 mitted by fleas from one rat to another and from rats 

 to man. Great epidemics of this disease have swept 

 across Europe in the past, and it is estimated that 

 during the fourteenth century 25,000,000 people died 

 of bubonic plague. A few outbreaks have occurred in 

 this country, but they were quickly suppressed by ex- 

 terminating the rat and killing other infected animals. 

 Rats that live in drain ditches and sewers come out 

 at night and spread the germs of typhoid fever and 

 other intestinal diseases. 



Only by patient and persistent effort and the co- 

 operation of all can a community be kept free from 

 rats. Trapping them by combined action of all the 

 members of a community is the best method. Barium 

 carbonate mixed with food is recommended by the 

 U. S. Department of Agriculture as an effective rat 

 poison. The chief objections to the use of poison are 

 its dangers to human beings and animals, and the 

 possibility that rats eating it may die in inaccessible 

 places, where their decaying bodies will cause bad 

 odors. Cutting off the food supply limits the number 



