EASTERN LIMIT OF SPREAD. 137 



THE EASTERN LIMIT OF MIGRATIONS. 



As will be found stated elsewhere, the eastern limit of their range, al- 

 though marked by no permanent, natural barrier, such as a mountain 

 range or large body of water, is probably as well detined and as rigidly 

 fixed as it is by the forest-clad Sierra of Nevada on the west. Although 

 the highest ranges and loftiest peaks of the Eocky Mountain belt from 

 British America to New Mexico seem to offer no impediment to their 

 movements, and to form no part of the boundary -line of their native 

 breeding grounds or migrations, yet we can mark along the level or un- 

 dulating prairies of Minnesota, Iowa, Missouri, Indian Territory, and 

 Texas, almost with the precision of a surveyor, the utmost limit of their 

 movements eastward. Why a swarm driven by a northwest wind, when 

 approaching this limit, should drop down rather than move onward to 

 the east of the Mississippi will be discussed elsewhere. All we have to 

 deal with here is the fact which authorizes us to fix this line as the east- 

 ern boundary of their movements, not of one or two years, but gener- 

 ally. If it were the limit of the flight of invading swarms, we might 

 conclude that it simply marked the terminus of their flight, and hence 

 had no real limital value, but when resulting swarms are seen in hundreds 

 of cases stopping at it, although not exhausted or wearied by length of 

 flight, we may reasonably conclude that this is the limit of their range, 

 whether we can assign a satisfactory reason for it or not. 



It is due to the memory of Mr. Walsh, formerly State entomologist of 

 Illinois, to state here that he was the first who expressed the belief that 

 these locusts would never cross the Mississippi Eiver. This opinion 

 was stated in the following language, in October, 1866 (Practical Ento- 

 mologist, vol. i, p. 5) : 



I do not think that it is at all probable that these Colorado grasshoppers will ever 

 cross the Mississippi, as the Colorado potato-bug has done, and pass onward to the 

 Eastern States. In the latter case there were physical obstacles to the eastward spread 

 of the insect previous to the settlement of the Rocky Mountain region. But in the 

 case of the Colorado grasshopper there was no such obstacle; and as they [have] not 

 heretofore spread eastward there is no reason to believe that they will do so hereafter. 



In his "first annual report" as acting State entomologist of Illinois, 

 published in 1868, is a somewhat lengthy article on these insects, in 

 which he discusses more at length this subject, fixing the eastern limit 

 of their range in Iowa in Polk County, or '* 115 miles" west of the Mis- 

 sissippi. He mentions also their eastern extension in Minnesota to 

 Anoka County 5 in Southern Iowa, to Clarke and Page Counties; in 

 Northwestern Missouri, to Nodaway County ; in Texas, to Eed Eiver, 

 Hunt, Austin, and Lavaca Counties. As will be seen hereafter, three 

 of these counties, Anoka, in Minnesota; Clarke, in Iowa; and Eed Eiver, 

 in Texas, mark the extreme eastern limit in their respective latitudes, 

 and the others adjoin or lie near the most eastern counties to which the 

 locusts have since extended their migrations. 



The eastern limit in Missouri is defined in Mr. Kiley^s account of the 



