METHODS OF CIRCUMVENTING VERMIN 145 



assembling in the valley and killing " at least 45,000 

 mice a day." The Survey came to the rescue in this 

 plague experience. The Department Report for 1908, 

 which tells the story, declares : " Poisoning is the most 

 generally applicable, cheapest, and most certain means 

 for controlling mouse plagues at present known." It 

 also recites the various methods of combating the 

 plague, poisoned green alfalfa placed in the runs and 

 burrows being " fatal to practically all the mice, in the 

 areas treated." As field mice produce, annually, from 

 two to six litters, which may average six, running oc- 

 casionally to a dozen or more, the early young breeding, 

 probably, the same year, the danger of overmultiplica- 

 tion is always near. The United States government 

 has consistently favored holding Nature's balances, as 

 far as may be, arguing that the few chickens which 

 roving vermin may kill are nothing as against the losses 

 that may follow the persistent destruction of the pre- 

 daceous birds and mammals, whose chief food is worse 

 enemies of man. Concerning large enemies of mice in 

 the incident reported, the report says that probably 3000 

 of these appeared in the valley during the mice plague, 

 and adds : " It may be assumed that these 3000 natural 

 enemies would each destroy an average of 15 mice a 

 day, or 450 a month, or collectively would kill 45,000 

 mice a day, or 1,350,000 per month. This number, vast 

 as it is, is far too small to put an end to a well-established 

 plague, although more than ample to check a plague 

 during its early stages, or to completely wipe it out 

 after the numbers have been materially reduced by 

 poisons or other agencies." 



What is known as " the plague mouse " almost always 

 L 



