08 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
G. THE HEIGHT AT WniCH SWAEMS MOVE. 
Iu studying the flights of 0. sprctus over the temporary region certain 
facts, as the sudden appearance of swarms iu the afternoon of bright, 
clear days at certain points, when nothing had been seen or heard of 
them over the surrounding area; and large swarms departing from one 
section in a certain direction over a well-settled area, though nothing 
could be seen or heard of them in that direction, &c, led us to investigate 
this subject also with special care, to ascertain, if possible, how this was 
to be accounted for. 
There appeared to be no other possible solution of the problem than 
that the swarms flew at such a height as to be entirely out of sight. 
Observations of flying swarms soon made it apparent that although, 
when seen at some distance approaching and flying rather low, the 
swarm is observed as a mass resembling a cloud, yet when passing over- 
head the locusts arc seen only as individuals. This fact rendered it ev- 
ident that the height at which it was possible to see thein was much 
less than would generally be supposed from the descriptions of locust 
flights given by t ravelers in the Old World. It is also probable that what 
is said here in reference to the invisibility of swarms of Rocky Mount- 
ain locusts is not fully applicable to swarms of the larger Oriental spe- 
cies. 
It is not possible to determine with any exactitude the height of 
swarms even when visible, as they 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, but 
more like a vast body of fleecy clouds, or, still more correctly, 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 at- 
tempts at measuring the height of swarms, and in some instances has 
succeeded in ascertaining pretty correctly the elevation above the sur- 
face, and also the depth of the swarm. But the only important 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. 
The facts already mentioned, which could be accounted for in no other 
way, and which were of repeated occurrence, render this not only highly 
probable, but almost certain, and we would be justified in assuming the 
affirmative even if we had no other evidence. 
But, as stated in our former report, the strongest evidence in favor of 
the view that they 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 
