282 GEOLOGICAL SURVEY OF THE TERRITORIES. 



and extends eastward much faster in a cold northerly than in a warm southerly lati- 

 tude. We have traced back the history of this insect as far as the year 1820 ; and in 

 all these forty-eight years, although no less than seven invasions of the country to the 

 east of the Rocky Mountains have taken place, namely, in 1820, 1856, 1857, 1864, 1866, 

 1867, and 1868. it has never yet got within one hundred and twelve miles of the Mis- 

 sissippi River ; and there is no reason to suppose it will ever do so for the future. 

 There must necessarily be some limit or other to the powers of flight of this insect. 

 It would be absurd, for example, to suppose that it could fly, in one season, as far east- 

 ward as England or France, or even as far as the Atlantic Ocean. Consequently, as it 

 can be proved by historical records, that it has never, within the last half century, 

 reached within one hundred and twelve miles of the Mississippi, the fair and reason- 

 able inference is that it never will do so in the future. 



His views in regard to the hatching grounds or nativity of this insect 

 are strongly contested by William N. Byers, esquire, of Denver, who has 

 given the subject considerable attention. While Mr. Walsh believes the 

 mountain caiions are the points from which they issue, (with which I at 

 first agreed,) Mr. Byers, on the contrary, thinks they come from the plains 

 west of the Bocky Mountains. I will hereafter give my present opinion, 

 my first view having been somewhat modified by subsequent investiga- 

 tion. I have received from Mr. Byers a full statement of his observations 

 in regard to the history and habits of this insect, from which I make the 

 following quotations: 



They generally enter Colorado from some point between north and west, usually 

 about north 30° west. The most destructive flight we ever had here was in 1864. 

 Early in the season we heard of great swarms of grasshoppers hatching out upon the 

 plains of Montana, in the valleys of the Three Forks of the Missouri River, and along the 

 Yellowstone. Later we heard of their progress south and east. In August I was with 

 Professor Parry (now botanist of the Department of Agriculture) and Velie in an 

 attempt to ascend Long's Peak. On the 21st we returned to the plains at the mouth of 

 St. Vrain's Canon, about fifty miles north of Denver. A man came up the valley, in the 

 evening, to where we stopped, and reported the grasshoppers entering the valley from 

 the north. The next morning, August 22d, I rode down the valley and found portions 

 of the corn fields and grass blackened by their nnmbcrs. About five days after, 

 August 27th, the swarm reached Denver, darkening the sky and often covering the 

 streets. They devoured corn, tomatoes, potato vines, onions', &c, almost entirely, and 

 within the space of three to five days. The column moved on, say ten miles per day, 

 and left the (then) settled portions of Colorado within the valley or basin of the 

 Arkansas. We heard no more of them. But myriads remained here, or continued 

 arriving from the northwest, and deposited their eggs in plowed fields and upon rolling, 

 sandy, and gravelly land, where the sod was unbroken. In September and October 

 most of them died. The first swarm devoured all that was green, but Colorado's green 

 crops in August are of small value compared with those harvested in July and up to 

 August 10th. In March following the eggs deposited by them began hatching, first upon 

 sandy, and gravelly hillsides, facing the sun, and later in plowed fields and in colder 

 soils, the outcoming brood reaching too late in May. In walking over the ground the 

 young swarm rose about the feet like a gray mist or dust, the little creatures hopping 

 away like fleas. Where numerous they literally devoured every green thing. If a 

 wheat field (in which none were hatched) was attacked they moved across it, or from 

 the circumference to the center, with the regularity and the effect of advancing flames. 



The flights of 18ii4 destroyed corn and other late crops; the young of 1885 ate up 

 wheat and other small graius. The comparative damage was probably as one to four, 

 the young brood being far the Avorst, simply because their opportunity was greatest. 

 Generally they move leisurely ; their direction influenced largely by the direction of 

 the wind. In fact I attribute mainly their general course to the prevailing winds which 

 come during that portion of the season when they fly most, almost invariably from the 

 northwest. Along toward noon, in bright, warm days, they rise by circular flights, 

 each seeming to act individually, to a considerable height, and then sail away, with 

 tolerable regularity, in one general direction. If there is no wind, many of them con- 

 tinue whirling about in the air, like bees swarming, but, away beyond, myriads can be 

 seen moving across the sun toward the southeast, looking like snow-flakes. If there 

 is a change in the atmosphere, such as the approach of a thunder-storm, or gale of 

 wind, they come down precipitately, seeming to fold their wings and fall by the force 

 of gravity, thousands being killed by the fill, if it is upon stone, or other hard surface. 

 If not interrupted by such causes they desceud during the afternoon. 



The swarm of August, 1864, and the brood of April and May, 1865, are the only gen- 

 eral visitations that have scourged Colorado. Similar ones, both flights and broods, 



