388 INFLUENCES OF CULTIVATION 



family, peculiar to the district. Only when cultivation 

 pushed westwards and the home of the Beetle was invaded, 

 did it turn from the wild Sand Bur to the cultivated species, 

 with appalling results. The abundance of the cultivated 

 crop and its continuous distribution throughout the States 

 gave the Beetle extraordinary opportunities for increase 

 and spread, especially towards the east where cultiva- 

 tion was more intense. In 1859 it entered Nebraska. In 

 1 86 1 it had reached Iowa; in 1864 and 1865 it crossed the 

 Mississippi, entering Illinois by at least five routes. Here 

 the distinctive influence of high cultivation was interestingly 

 shown, for in the northern part of the State where potato- 

 crops were more frequent than in the southern, it was noticed 

 that "in marching through Illinois, in many separate columns, 

 just as Shearman marched to the sea, the southern columns 

 of the Grand Army lagged far behind the northern columns.' 

 Wisconsin was invaded by the conqueror and possessed by 

 the autumn of 1866. In 1867 it crossed the borders of Indiana. 

 In 1869 it appeared in Ohio. In the following year it crossed 

 into Canada, appearing in the province of Ontario, swarming 

 in the Detroit River, and making passage across Lake Erie 

 on "ships, chips, staves, boards, or any other floating 

 object which presented itself." In 1874, it had reached the 

 Atlantic and multiplied with such rapidity that in September 

 1 876, Beetles were washed ashore on the coast of Connecticut 

 in such numbers as to poison the air, and a New London 

 vessel was boarded in such force at sea that the hatches 

 had to be shut down. Railway trains were stopped owing 

 to the slipping of the wheels on the rails, caused by the 

 slaughtered thousands. A summary of the exploits of the 

 Colorado Beetle gives a vivid notion of the influence of 

 cultivation in increasing the range and numbers of favoured 

 species. It travelled from its native region in Colorado 

 to the Atlantic ocean, covering at least 1500 miles in the 

 sixteen years from 1859 and 1874; its annual rate of travel 

 averaged 99 miles, but so distinct was the influence of 

 cultivation that in the wilder western States the rate of 

 progress was less than 50 miles a year. 



America shows more clearly than the old countries the 

 actual transformations in animal life wrought by the spread 

 of civilization, for there we can still watch the struggles of 



