SOME SOURCES OF OUR FAUNA AND FLORA 



299 



Extensive ravages first occurred above and about Lovelocks. In 

 May, 1907, fields on the Rogers ranch, 5 miles below Lovelocks, were invaded 

 from lands farther up the valley, the progress of the mice being plainly 

 marked, as the fields above the Rogers ranch suffered first. The move- 

 ment of this great body of mice, it should be noted, was a gradual, scattering 

 progression, first by a few and later by increasing numbers, untU the greater 



part had moved to fresh fields By October, 1907, a large part of 



the cultivated lands in this district had been overrun by vast numbers of 

 mice The height of the abundance was reached in November, when 



Fig. 449. — Map of potato beetle invasion, with dates of arrival at some 

 localities. After Tower. 



it was estimated that on many large ranches there were 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 honeycombed, and the scene was one of 



desolation By November they had destroyed so large a percentage 



of the plants that many fields were plowed up as hopelessly ruined 



By January, 1908, in fields where the mice had existed by thousands the 

 previous summer and fall, comparatively few, possibly 200 to 500 to each 

 acre, remained. The border of the destroyed district was about 6 miles 

 below Lovelocks, and the mice were gradually moving down the valley. 



The exact data regarding such invasions of adjacent territory 

 by animals and plants are, as a rule, only available when the 



