HEIGHT AT WHICH SWARMS MOVE. 
99 
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 
reasonable to suppose that a height which would render them invisible 
would render a swarm of locusts invisible when passing overhead, as the 
latter, as before stated, are seen, not as a mass, but as individuals. 
The statement by Mr. Byers, 197 that while on Long's Peak he observed 
swarms flying over as high as the eye could reach, and that of Mr. Put- 
nam to the same effect, show very conclusively that it is possible for 
them to fly as much above the reach of the natural eye as the tops of 
Long's and Parry's Peaks are above the plains of Kansas aud Nebraska — 
about 10,000 feet. The writer has taken specimens on the very summit 
of Pike's Peak, brought down, probably, by a preceding shower of rain, 
yet no swarm had been noticed passing over by the Signal Service offi- 
cer in charge of the station. The Signal Service officer at Bismarck 
states that with a glass he observed a swarm on one occasion flying 
above the clouds. 
The careful and interesting observations of Dr. A. L. Child, of Platts- 
mouth, Nebr., whose letter has already been quoted, appear to settle 
this point beyond dispute ; and although we have other evidence point- 
ing to the same conclusion, we deem it unnecessary to present it. "We 
conclude, therefore, that as a general rule swarms of C. spretus are not 
visible to the natural eye at a height of more than seven or eight thou- 
sand feet above the plains of the temporary region ; that in their long 
flights, when invading and returning, they not only often, but probably 
generally, fly, during part of the distance traversed, so high as to be out 
of sight, and that sometimes they pass above the lower and rain clouds, 
though as a general rule it is only during clear weather, when the sky is 
cloudless, that they fly. 
If we are correct in these conclusions, they, together with the fact that 
the locusts also occasionally fly at night, will enable us to understand 
why it is so difficult to trace the flight of a swarm, and will also serve 
as an explanation of much of the mystery that has surrounded their 
movements. 
It is somewhat strange that this question should have been overlooked 
by European entomologists, when it would have sufficed as an explana- 
tion of some of the points long in controversy. 
Koppen 196 says : 
The height of the flight is quite variable ; they direct themselves according to the 
wind and weather, and may vary during the continuation of the flight. I observed 
the flight of locusts soon after their last moult ; it was in the evening and on a mod- 
erate west wind ; they mostly flew at a height of 15 or 20 feet ; single individuals only 
reached a height of 40 or 50 feet. 
w First Report, 144. 
1! » Heuschr. Sud-Russ, 52. 
