No. 6.] RILEY — ROCKY MOUNTAIN LOCUST. 869 



of the 100th meridian. It is the more fertile and thickly-settled 

 country south and east of the limits indicated which suffer most, 

 both from the insects which sweep over it and from the young that 

 hatch in its rich soil ; and it is principally this country which I 

 have designated as being outside the insects' native home, and in 

 which it can never become a permanent resident. The species 

 does not dwell permanently even in much of the country north 

 and west of those lines, but it flourishes more and more toward 

 the northwest. In short, the vast hot and dry plains and prairies 

 of Wyoming, Dakota, and Montana, and the immense regions of 

 a similar character in British America, comprising what is known 

 as the third prairie plateau or steppe, are congenial breeding- 

 grounds, and supply the more disastrous swarms which devastate 

 the lower Missouri and the Mississippi valleys. That Northwest 

 country may be depicted as a vast undulating prairie sea, now 

 stretching in sandy barren tracts which bring forth little else 

 than the cactus or sage-bush ; now rolling for hundreds of miles, 

 and covered with the buffalo grass (Bucloe dactyloides) and 

 other short nutritious grasses, and again producing a ranker 

 prairie growth wherever there is increase of moisture. Another 

 peculiarity of that country is that though the spring opens as 

 early, even away up in the valley of the South Saskatchewan, as 

 it does in Chicago, yet the vegetation often becomes parched up 

 and burned out by the early part of July. Now, Caloptenus 

 spretus, though coming to perfection in high and dry regions, is 

 nevertheless fond of succulent vegetation, and instinctively seeks 

 fresh pastures whenever those of its own home are dried up. It 

 may sometimes happen, indeed, that the species will die in im- 

 mense numbers if the scant vegetation where it breeds should dry 

 up before the acquisition of wings, just as another species {(Edl- 

 poda atrox) has perished in immense numbers the present season 

 in California by the excessive drought that has prevailed there ; 

 but ordinarily the insects will be full grown and fledged before 

 the parched season arrives, and the ample wings of the species 

 prove its salvation. Again, it may become so prodigiously mul- 

 tiplied during certain seasons that everything green is devoured 

 by the time its wings are acquired. 



"In either case, prompted by that most exigent law of hunger, 

 — spurred on for very life, — it rises in immense clouds in the air 

 to seek for fresh pastures where it may stay its ravenous appe- 

 tite. Borne along by the prevailing winds that sweep over these 



