PACKARD] THE LOCUST EAST OF THE PLAINS. 635 



The young do not leave the place of their birth mitil after the first 

 month, but huddle together, not scattering, as most young insects do, they 

 being gregarious at the outset. The small bauds then unite into larger 

 oues, and these mass into enormous armies. They are exceedingly 

 ravenous, feeding upon each other when other food is exhausted. 

 Riley says that " the young insects move, as a rule, during the warmei 

 hours of the day only, feeding, if huugry, by the way, but generally 

 marching in a given direction until toward evening. They travel in 

 schools or armies, in no particular direction, but purely in search of 

 food, the same school often pursuing a different course one day to that 

 pursued the day previous." In Missouri, the young moved in a general 

 northerly direction. They seldom move, when half-grown, " at a greater 

 rate thau three yards a minute, even wheu at their greatest speed, over 

 a tolerably smooth and level road, and not halting to feed. They walk 

 three-fourths of this distance and hop the rest." It is in the young 

 wingless condition that the locust is most to be feared, and, on the 

 other hand, most easily subdued. 



THE ROCKY MOUNTAIN LOCUST NOT PERMANENTLY ABUNDANT AND 

 INJURIOUS EAST OF THE PLAINS. 



It has been abundantly proved by Professor Riley and others that the 

 locust will not be destructive east of longitude 93° or 94:^, namely, the 

 western edge of the Mississippi Valley. We have seen that the progeny 

 of the swarms from the plains lying on the flanks of the Rocky 

 JMountains which at intervals infest the western border of the Mis- 

 sissippi basin generally return northwestward. The cause of their north- 

 westward migration is in all probability due to the prevailing southerly 

 and easterly winds of June and early July ; but those that are left are 

 said to be enfeebled and degenerated. Mr. Riley attributes this to the 

 low altitude and moisture of the Mississippi Valley, the locust flourish- 

 ing and most prolific in the dry elevated plateaus of the Rocky Mount- 

 ains. Professor Riley thinks that the length of the summers of the 

 western Mississippi States as compared with the short hot summers of 

 the plains another cause of its inability to live permanently east of the 

 plains in large numbers. To use Riley's own words : 



Assaraing that I have correctly placed the native home of the species in the higher, 

 treeless, aud uninhabitable plains of the Rocky Mountain region of the northwest, 

 aiul that it is subalpiue, we may perhaps find, in addition to the comparatively sudden 

 change from an attenuated and dry to a more dense and humid atmosphere, another 

 tangible barrier to its permanent multiplication in the more fertile country to the 

 southeast in the lengthened summer season. As with annual plants, so with insects 

 (like this locust), which produce but oue generation annually, and whose active exist- 

 ence is bounded by the spring and autumn frosts, the duration of active life is pro- 

 portioned to the length of the growing season. Hatching late and developing quickly 

 in its native haunts, our Rocky Mountain locust, when born within our borders (and 

 the same will apply in degree to all the country where it is not autochthonous), is in 

 the condition of an annual northern plant sown in more southern cliuies; and just as 

 this attains precocious maturity and deteriorates for want of autumn's ripening in- 

 fluences, so our locust must deteriorate under such circumstances. If tliose which 

 acquired wings in Missouri early last June bad staid with us long enough to lay eggs, 

 even supposing them capable of doing so, these eggs would have inevitably hatched 

 prematurely, aud the progeny must in consequence have perished. 



The fact that some changes are undergone by the eastern progeny of 

 the l^cky Mountain locust is substantiated by two good observers, 

 quoted by Mr. Riley, as follows: 



Mr. Riley is of the opinion that the grasshoppers run out in a few generations after 

 they leave their native sandy and gravelly feoil. My experiments, so far as they go- 

 verify that opinion. For several years I have caught grasshoppers during early sum, 



