IMPOKTAKT FLIES 117 



in feeding for two weeks without getting caught. In this 

 case no more eggs will be laid, and the pests will vanish. 

 Possible multiplication. Allowing ten days for eggs to 

 become adults, and, for convenience, ten days of feeding 

 between emergence and oviposition, figuring that a fly lays 

 one hundred and fifty eggs at a batch and lives to lay six 

 batches, compute the increase of a pair of flies beginning to 

 lay May first. Half the progeny are supposed to be females. 

 Test the following figures : 



May K> 152 flies 



20 302 flies 



30 11,702 flies 



June 10 34,302 flies 



20 911,952 flies 



30 .. 6,484,700 flies 



July 10 72,280,800 flies 



^ 20 325,633,300 flies 



30 ! 5,746,670,500 flies 



The common-sense question is, Why not let this pair of 

 flies catch themselves in May ? This rapid increase also means 

 that anything short of extermination is hardly worth the effort. 

 A fly is possessed of no more cunning than shot rolling down 

 a board, and the last pair will run into a trap as easily as the 

 first. Why not let them all catch themselves ? 



Hibernation. Very few house flies survive the winter in 

 Canada and the northern states, and these hibernate as young 

 adults in cracks about buildings. They come out of winter 

 quarters ravenously hungry and feed for about a week, at 

 least, before beginning to lay. If at this critical time every 

 household had some effective form of outdoor trap ready for 

 them, every early spring breeder would be caught, and the 



1 This last figure would equal about 143,675 bushels of flies from one pair 

 in three months. If we continue the breeding through August and Septem- 

 ber, the figure is 1.096,181,249,310,720,000,000,000.000 flies. 



