﻿OF THE STATE ENTOMOLOGIST. 81 



As flight is not consecutive day after day, but often impeded by 

 bad weather, and as it is not continuously in one direction, the aver- 

 age rate is not more than 20 miles a day. It is also most variable 

 and at times reaches a maximum of between two and three hundred 

 miles daily. 



DIRECTION OF FLIGHT. 



The wind was quite changeable during the period of invasion, and we 

 find the insects, at one time or another, traveling in nearly all possible 

 directions, except due west. Yet, if we except the departing swarms 

 which flew from N. W. Minnesota in July, the direction of the invad- 

 ing hosts was, as I believe it always has been and always will be, con- 

 spicuously S. and S, E. The exceptions were principally during the 

 first week in August, when they swept S. W. from Minnesota over 

 parts of Iowa and Nebraska; and two months later when they were 

 carried N. E. into our S. W. counties. 



INFLUENCE OF THE WIND IN DETERMINING THE COURSE OF LOCUST SWARMS. 



That excessive multiplication and hunger are the principal causes 

 of migration from the native home of the species, and that the pre- 

 vailing winds determine the course therefrom, I have endeavored to 

 show (Reps. 7, p. 104; 8, p. 112). That all these influences very 

 largely determine the return migration when the insects hatch out in 

 the Mississippi Valley is also doubtless true; and it is interesting to 

 note in this connection that, according to observations, covering a 

 period of from two to five years, furnished by General Myer, at the 

 request of Dr. A. S, Packard, Jr.,* the prevailing winds in May and 

 June, within the region subject to invasion, are from the Gulf of 

 Mexico, or from the S. E. and 8., i. e. in the opposite direction, prevails 

 later in the season. Yet, to assume that the migrations are solely 

 dependent for direction on the winds would be incorrect, as there is 

 cumulative evidence (much of it recorded in these Reports) that when 

 once the migration has commenced, adverse winds only retard, but 

 do not materially change its course. 



LOCUST FLIGHTS EAST OF THE MISSISSIPPI. 



To the unscientific mind there are few things more difficult of 

 apprehension than that species, whether of plants or animals, should 

 be limited in geographical range to areas not separated from the rest 

 of the country by any very marked barriers, or by visible demarca- 

 tions. Yet it is a fact well known to every naturalist, and the geo- 



' The Destructive Locust of the West," Am. Naturalist, Vol- xi, p. 27. 

 ER-6 



