National Geographic : 1909 May
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. D AMAGE 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,ooo to 12,ooo 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.