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the locust swarms of Ohio, Illinois, Georgia, and South Carolina ; 

 and specimens sent him showed at once that they were not the 

 Rocky Mountain Locust, but species more or less common every 

 year in the localities where they occurred, and comparatively 

 harmless. Hence the idea held by the unscientific that the 

 Western locust plague had overstepped the limits entomology 

 prescribes to it, and is upsetting the conclusions of science, is 

 unfounded. The causes which limit the eastward flight of the 

 Rocky Mountain Locust are briefly these : — The power of flight 

 of any insect that has a limited winged existence must somewhere 

 find a limit. Experience has shown that these locusts have never 

 extended, in a general way, east of a line drawn a little west of 

 the centre of Iowa, and, as long as the present average condi- 

 tions of wind and climate prevail, it is reasonable to suppose that 

 they never will. The species is at home and can come to perfec- 

 tion only in the high and dry regions of the northwest, where the 

 winters are long and cold, and the summers short ; and whenever 

 it migrates and oversweeps the country to the south or southeast, 

 in which it is not indigenous, the changed conditions are such that 

 the first generation hatched out in that, to it, unnatural climate, 

 either forsakes it on the wing, or perishes from disease or the 

 attacks of insect enemies. 



Mr. Nipher remarked that one expression in Prof. Riley's pa- 

 per appeared to him an unfortunate one — one well calculated to 

 mislead the unscientific — viz., that entomology "prescribes" the 

 limits of the locust plague. Past experience may have been of 

 such a nature that its limits may be predicted with some degree 

 of certainty. 



This idea was concurred in by Dr. G. Engelmann, who brought 

 up many cases to show that we can base such predictions upon 

 experience only. He mentioned the well known case of the 

 potato-beetle, which, when potatoes began to be cultivated in 

 Colorado, pushed its way eastward to the Atlantic States, and 

 may even reach Europe. The weeds of the Atlantic and middle 

 States are largely from Europe, and mainly from England ; those 

 of the Pacific coast are largely from Spain. A leguminous 

 plant, Lespedeza striata^ now exceedingly common from Vir- 

 ginia southward, came originally, no one knows how, from South 



