146 EEPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



otherwise shrouded in uncertainty , still, he did not feel warranted in 

 venturing more than the suggestion that such might possibly be the case. 

 Although all direct observations of which we have any knowledge seem 

 to contradict this idea, yet there are some facts in reference to the flights 

 along the eastern limit of their range which are difficult to explain un- 

 less we suppose a change in direction without alighting 5 such, for ex- 

 ample, as swarms flying in an easterly direction at this limit, which are 

 never heard of beyond it or on the east side of it 5 also, swarms seen 

 coming from an easterly direction at points along this limit which were 

 never heard of before being seen passing westward. It is true that a 

 large number of such cases can be accounted for by the very probable 

 supposition that those going eastward came down unnoticed, which we 

 found to be a very common occurrence, even to a degree which could 

 scarcely be believed by those who have not had an opportunity of observ- 

 ing the fact. Others can be accounted for in other ways, yet after all 

 these eliminations there are still some cases left which can scarcely be 

 accounted for without supposing a change in the direction of flight with- 

 out alighting. 



As is shown further on, there are instances where two swarms were seen 

 moving in different directions at the same time, one in an upper current 

 and the other in a lower -, also, to one case where a swarm was flying south 

 in an upper current, while a lower current was moving in an opposite 

 direction. It is by no means unreasonable to suppose that in some cases 

 the swarm descending or ascending gradually reverses its course or moves 

 with the other current'. In reference to the double flight which he ob- 

 served on July 2G at Ponca, Nebr., Professor Aughey remarks, *' that 

 at the point or line where the two currents met the locusts seemed to 

 intermingle." 



The solution of these minor problems is of the greatest importance, 

 for their determination virtually determines the chief theory in relation 

 to the locust migrations. If their alighting is caused by the difference 

 in temperature of the opposing winds or some other atmospheric condi- 

 tion than simply the direction in which it moves, it follows as a matter 

 of course that they do not drop simply because they are prevented from 

 moving on in the direction they wish to go — a point on which the theory 

 of the '^ returning swarms" chiefly hinges. We are satisfied that the 

 facts so far ascertained in reference to these points, taken together, in- 

 dicate very clearly that their pauses cannot be fully explained by differ- 

 ences in temperature or simple atmospheric changes, and that the only 

 reasonable explanation which can be given for many of their stoppages 

 is, that they are prevented by opposing winds from moving on in the di- 

 rection they desire to go. Still, on account of the very important bear- 

 ing it has upon the locust problem, and upon the possibility of our pre- 

 dicting with certainty their movements in advance, we think it deserves 

 a more thorough study and additional investigation. 



