﻿112 EIGHTH ANNUAL REPORT 



numbers." Regarding the western boundary, nothing struck Prof. 

 Thomas* as more singular than the few specimens of spretus collected 

 west of the mountain range by the Hayden Geological Survey, from 

 which he infers that the line of the survey was along the southwest 

 border of its district. Mr. J. D. Putnam, of Davenport, Iowa, who 

 spent July, August and September of last Summer in Utah, also in- 

 forms me that he did not meet with a single specimen. 



This whole subject of the original source of the swarms that at 

 times lay our fertile valley country under such severe contribution is 

 yet somewhat obscure, and should be investigated by the Govern- 

 ment. Meanwhile we must shape our views by the facts in our pos- 

 session. 



[4.] Now that we know where the bulk of the eggs were laid, it 

 seems more than likely that the principal reason of the retarded pro- 

 gress of the 1874 swarms, by the time they reached east Kansas and 

 Missouri was due to the fact that they were more busily engaged in 

 ovipositing than they had previously been. Moreover they there 

 strike a country more or less timbered, with nioister atmosphere, and 

 less violent and more changeable winds. 



CONDITIONS or MIGRATION. 



The exodus from the country where the species is not indigenous 

 would seem to be instinctive and determined perhaps by the injurious 

 effects of the uncongenial climate. The cause of the migrations from 

 its native northwest home I discussed in my last Report (p. 164). Hun- 

 ger and strong winds are the principal ; but the conditions which per- 

 mit extended flights and migrations southeast are doubtless, in great 

 part, meteorological, and as throwing light on these conditions, the 

 following from an interesting review of the locust question by Mr. W. 

 H. Miller, and published in the Kansas City Journal of Commeroey 

 will prove suggestive : 



Since it has been well ascertained that dry weather is a necessity to its prosperous 

 existence, it is concluded that dry seasons are necessary to its invasions. There is much 

 force in this conclusion, for since the moisture of the western States and Territories is 

 borne to them from the Gulf of Mexico by southerly winds, a dry season indicates a 

 diminishing of these winds, which removes two important impediments in it.^ advance 

 —moisture and opposing currents of air. it is also held by entomologists that it mi- 

 grates only when the vegetation of its habitat becomes exhausted. A diminished south- 

 erly wind, and a dry season on our western plains, would favor this result, for since 

 the moisture of tliis region comes from the Gulf, a dry season on the plains and short 

 vegetation there would indicate a dry season and short vegetation in the latitude where 

 we have supposed its habitat to be. 



* Preface to his Report iipou the Collections of Orthoptera made in Nevada, Utah, California, Col- 

 orado, New Mexico, and Arizona, in 1871, 1872, 1873 and 1874, by Hayden's Geol. Siirv. of the Terr. 

 (1876). 



