1877.) The Rocky Mountain Locust. 669 
ishes 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 Amer- 
ica, comprising what is known as the third prairie plateau or 
steppe, are congenial breeding-grounds, and supply the more dis- 
astrous swarms which devastate the lower Missouri and the Mis- 
sissippi 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 
(Bueloe 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 be- 
‘comes 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 immense numbers if the scant vegetation where it 
breeds should dry up before the acquisition of wings, just as an- 
other species ( Ædipoda 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 prodig- 
iously multiplied during certain seasons that sound 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 ap- 
petite. Borne along by the prevailing winds that sweep over 
these immense treeless plains from the northwest, often at the 
rate of fifty or sixty miles an hour, the darkening locust clouds 
are soon carried into the moist and fertile country to the south- 
east, where with sharpened appetites they fall upon the crops, a 
plague and a blight. Many of the more feeble or of the more re- 
cently fledged perish, no doubt, on the way; but the main army 
succeeds, with favorable wind, in bridging over the parched 
country which affords no nourishment. The hotter and dryer 
the season, and the aoee the extent of the drought, the earlier 
