132 THE CANADIAN ENTOMOLOGIST. 



The observations made, so far, give no special reasons for these 

 migrations, unless it be the unusual abundance of the species and the 

 consequent scarcity of food in its native regions. One or two favorable 

 seasons cause the insect to increase to an immense extent, and when they 

 find the supply of food failing them, they mount into the air in countless 

 millions, and, favored by a westerly or north-westerly wind, sail off towards 

 the settlements in search of " fresh fields and pastures new." Such is the 

 principal reason given by Packard, though he says possibly the reproductive 

 instinct may also be concerned. And he does not think that these move- 

 ments can be the result of a real migratory instinct, because their 

 migrations (as well as those of the locusts of the old world) are periodi- 

 cal, long intervals sometimes existing between them, so that the develop- 

 ment of a migratory instinct would be impossible. If once partially 

 implanted, the long succession of non-migratory years would effectually 

 break up the germs of such an instinct. 



Another curious fact in connection with these locusts is, that the gen- 

 eration born in the region to which the species has migrated the previous 

 year, shows a tendency to return north and west towards the primal 

 habitat. This has been proved by repeated observation. One reason for 

 this is found to be the prevalence of favorable winds at that particular 

 season in the regions where these locusts are produced ; for locusts, and 

 indeed, all migratory insects, are dependent to some extent upon the winds 

 for assistance and direction in their migrations. This is true for locusts 

 all over the world ; they are brought by the wind and taken away b# the 

 wind. A striking instance of this fact is given in the account of the great 

 Egyptian plague of locusts, in the Book of Exodus. 



So with our American migratory locust. The general direction of the 

 winds on the eastern slopes of the Rocky Mountains and on the plains 

 is, during July and August, west or northwest. These are the months 

 during which the locusts come down from their mountain home to invade 

 the cultivated plains of the border States. And when the generation of 

 which these are the parents attain the winged state, in the following June, 

 it has been found that the prevailing winds are from the south and south- 

 east, and thus are favorable to the flight of the locusts in a northerly or 

 westerly direction 



As regards their powers of flight, it has been proved by experiment 

 that the locust, when it has a favorable wind (and it rarely flies at any 

 other time), does not fly faster than the wind, but merely uses its wings to 



