144 REPORT UNI'lED STATES ENTOMOLOGICAL COMMISSION. 



Standing this iudefiniteness it includes a very large number of move- 

 ments not embraced by either of the other terms, and comprises most 

 of the movements east of the mountains in 1877. 



The Jieight at tvhich swarms move. — To determine this with any exacti- 

 tude is almost an impossibility, as the swarms do not move in broad 

 sheets, as many who have never observed a flight imagine, nor are they 

 generally in a compact body whose boundary is well defined, forming a 

 clear line 5 but more like a vast body of fleecy clouds, or still more cor- 

 rectly, a cloud of snow-flakes ; often having a depth that reaches from 

 comparatively near the ground to a height that baffles the keenest eye 

 to distinguish the insects in the upper stratum. Professor Aughey has 

 made some attempts at measuring the height of swarms, and in some 

 instances has succeeded in ascertaining pretty correctly the elevation 

 above the surface, and also the depth of the swarm. But the only im- 

 portant question to be decided in reference to this point is, whether they 

 can and do fly at an elevation so great as to carry the entire swarm out 

 of view on a clear -day. 



There are some very strong reasons for believing that such is the case, 

 and as it enables us to account for some hitherto unexplained facts we 

 are disposed to assume that it is true, at least it is a point worthy of in- 

 vestigation. 



The Signal Service officer at Bismarck states that he observed a swarm 

 on one occasion flying above the (cumulus) clouds. Correspondents in 

 in their reports of flights often speak of them as being *' very high." 



In numerous instances they have been brought into view by field- 

 glasses when invisible to the natural eye ; and it was ascertained last 

 summer that they could be seen distinctly through smoked glass when 

 scarcely visible with the natural eye. 



But the strongest evidence in favor of the view that they very prob- 

 ably do often fly at an elevation above the plains of the. border States 

 which renders them entirely beyond the natural vision is the fact that 

 they can fly at that height. That it is no uncommon thing for cranes 

 and wild geese to fly north and south along the Mississippi at a height 

 which carries them entirely out of view is well known, as their notes 

 can frequently be heard overhead when the eye searches in vain for 

 them. At what elevation these move it is impossible to tell, but it is 

 not probable that it is much, if any, over two miles ; and it is reason- 

 able to suppose that a height which would render them invisible would 

 render a swarm of locusts invisible, as the latter are seen not so much 

 as a mass as individuals. 



Mr. W. M. Byers states that in 1868 "from the middle to the 25th of 

 August I was upon the Snowy Eange east of Middle Park and on 

 Long's Peak. There was a large daily flight of full-grown grasshoppers 

 from west-northwest reaching apparently to the highest limit of vision 

 when on the highest peaks." 



Mr. J. D. Putnam was on Parry's Peak in 1872 during the time a 



