A PLAGUE OF MICE* 



The work of the United States Government does not cease when irrigation 

 projects are completed and rich farms developed by the settlers. New prob- 

 lems arise, to meet which not an engineer, but the trained government biologist, 

 is required. The scourge of mice which in Nevada destroyed harvests worth 

 hundreds of thousands of dollars would be repeated many times were it not for 

 the genius of the experts of our U. S. Biological Survey, who have shown how 

 destruction by such pests may be averted in the future. 



DAMAGE by field mice attracted 

 the attention of the ranchmen 

 in the lower part of Hum- 

 boldt Valley, Nevada, early in the spring 

 of 1906, and became severe during the 

 following summer. In the fall and 

 winter of 1906-07 damage had increased 

 until fields here and there in the valley 

 were seriously injured. 



By October, 1907, a large part of the 

 cultivated lands in this district had been 

 overrun by vast numbers of mice. The 

 yield of hay had been reduced by one- 

 third ; potatoes and root crops were 

 largely destroyed; many alfalfa fields 

 were ruined by the mice eating the roots 

 of the plants, and the complete destruc- 

 tion of this, the chief crop in the valley, 

 was threatened. 



The height of the plague was reached 

 in November, when it was estimated that 

 on many large ranches there were from 

 8,000 to 12,000 mice to each acre. The 

 fields were riddled by their holes, which 

 were scarcely a step apart, and over large 

 areas averaged 150 to 175 to the square 

 rod. Ditch embankments were honey- 

 combed, and the scene was one of devas- 

 tation. Serious losses in hay and root 

 crops during the summer proved but a 

 slight forerunner of the damage which 

 began in the fall with the disappearance 

 of green food. Burrowing down about, 

 the plants, and extending their under- 

 ground runs from root to root, they 

 either killed or seriously injured the 

 alfalfa (see page 480). By November 

 they had destroyed so large a percentage 

 of the plants that many fields were 

 plowed up as hopelessly ruined (see page 



478). They attacked also the roots of 

 trees, seriously injuring or quite destroy- 

 ing orchards. They killed most of the 

 young shade trees planted along ditches, 

 and so completely girdled large Lom- 

 bardy and silver poplars (see page 481) 

 that in some cases they caused the death 

 of even such hardy trees. 



The great majority of ranchmen knew 

 neither what to expect from such great 

 numbers of mice nor how to check them. 

 Such plagues had usually been allowed 

 to run their course until brought to an 

 end by natural agencies. Hence it is not 

 surprising that in Humboldt Valley no 

 concerted or systematic efforts to sup- 

 press the plague in its earlier stages were 

 undertaken, but after the mice swarmed 

 in thousands over the fields many at- 

 tempts were made to destroy them by dis- 

 tributing wheat poisoned with phos- 

 phorus. These, however, were spasmodic 

 and generally proved futile, as the fields 

 experimented on were quickly reinvaded 

 from adjoining lands. While a few fields 

 favorably located were saved by early 

 poisoning, the results of such unsyste- 

 matic efforts amounted to practically 

 nothing in overcoming or even materially 

 checking the plague. 



The preparation in general use by 

 ranchmen consisted of wheat treated 

 with a strong solution of yellow phos- 

 phorus in carbon bisulphid, a cheap and 

 effective poison for field mice, but in- 

 flammable, explosive, and dangerous to 

 birds. As a result of its extensive em- 

 ployment in the valley, California quail, 

 an introduced species, were decimated, 

 and magpies, crows, meadow larks, and 



* Abstracted from "The Nevada Mouse Plague of 1907-08," by Stanley E. Piper. Farmers' 

 Bulletin 352, U. S. Department of Agriculture. 



