NORTHWESTWARD COURSE OF EARLY SUMMER FLIGHTS. 175 



Where have been the turning-points of all these movements 1 Apparently they must 

 have been either in Dakota and Iowa or up in the air. As for Iowa the records of 

 flights will be collected, I presume, by others. As for reports received from Dakota, 

 they do not help the matter much so far. The movements have been nearly the same 

 as in Minnesota, except that they began a day or two earlier. To all appearances, the 

 grasshoppers have spent the greater part of the time in the air since July 10. 



The early moveineDts of 1877 (omitting those in Minnesota) therefore 

 coincide precisely with those of previous years, and apparently justify 

 the conclusion that this northward flight is governed by some permanent 

 law, and will, under ordinary circumstances, be the course taken by the 

 broods hatched in the area designated. Whether the facts are sufficient 

 to warrant the opinion, now so generally entertained, that it is a law of 

 their nature to return to their nativ^e habitats is another question and a 

 very important one. It may be well, therefore, to present here the pros 

 and cons on the point which we have so far been able to gather by our 

 own observations and study of the species. 



1st. We have the fact sufficiently established that in the region desig- 

 nated the first movements of the resulting broods are toward the north 

 or northwest, and in the direction of the section which is now very gen- 

 erally conceded to be the native hatching-grounds of the swarms which 

 visit the border States. 



2d. The flights of the resulting broods in Colorado are often westward 

 across the mountains in the direction from which a large portion of the 

 invading hordes which visit that State come. 



3d. We have, if not absolute proof, at least satisfactory evidence that 

 in 1875 the departing swarms from a large portion at least of the area 

 designated moved northwest into Eastern Montana and British America, 

 thus reaching the region from which we have good reason to believe 

 their progenitors came. 



4th. In 1876 invading swarms from the northwest poured down in 

 vast numbers upon the fields and farms of the bordering States 

 and deposited their eggs over a widely-extended area. In 1877 we see 

 the resulting brood starting back in the same direction as those of 1875, 

 thus apparently forming a biennial cycle in their life-history. 



5th. As if led by some mysterious instinct to know that in this cli- 

 mate their progeny will be a degenerate and feeble race, these returning 

 swarms as a general rule refuse, or at least fail, to deposit their eggs in 

 this region. 



These are certainly strong arguments in favor of the theory men- 

 tioned, yet there are some facts which appear to stand opposed to it, 

 and although it is very plausible, cause us to hesitate before deciding 

 that it has been fully established. This question of migration, especially 

 in its relations to meteorology, will, however, be considered further on 

 in the present chapter and also in Chapter YIII. 



SOUTHWARD FLIGHTS IN 1877. 



As may be inferred from the data in Appendices 12 and 13, the south- 



