104 The Rocky Mountain Locust. 



they travel will depend on the force of the wind ; but it 

 is evident from the observations made in Dakota, where 

 their advance in 1875 was reported by telegraph, that they 

 often travel a hundred miles a day. Their minimum speed, 

 in tolerably calm weather, when the wind is scarcely felt 

 at the surface of the ground, can not be much less than 

 from eight to ten miles an hour. 



In the more western and northern parts of the locust 

 region, as in Minnesota, Dakota and Colorado, the direc- 

 tion of the departing swarms will be less constant, and 

 according as they develop late, or are the progeny of 

 swarms that came from other directions than the north- 

 west, they will either be carried by the wind or will 

 instinctively leave, in other directions. 



DESTINATION OF THE DEPARTING SWAKMS. 



That the swarms which leave the fertile country in 

 which they hatch and are not indigenous, pass by degrees 

 to the northwest, and reach into Northwestern Dakota, 

 Wyoming and Montana, the records clearly prove. That 

 they also reach far up into the northwest regions of 

 British America, the record of the nights of 1875 in 

 Chapter II (p. 42) also abundantly attests. It is also just 

 as certain that a large proportion of those which take wing 

 perish on the way from debility, the effects of storms, 

 and more particularly from the attacks of parasites ; be- 

 cause I proved by careful dissection in 1875 that a large 

 proportion of those which came to maturity and left the 

 western counties of Missouri, carried with them the germs 

 of destruction in the shape of Tachina eggs or the larvae 

 already hatched and of various sizes. Others again were 

 infested with the scarlet mites. We may very justly con- 

 clude, therefore, that a large proportion of the insects 

 which depart from the country invaded, perish on their way 



