238 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



the temporary region, viz, from the 5th to the 10th of May, in latitude 

 35^, and about 4 days later with each degree farther north. 



DIRECTION TAKEN BY SWARMS DEPARTING- FROM THE TEMPORARY 



REGION. 



While the swarms that invade the fertile parts of the West in late 

 summer and autumn move, as we have just seen (p. — ), conspicuously 

 to the south and southeast, the departing swarms in early summer 

 from the temporary region move as conspicuously to the north and 

 northwest. In short, as we have set forth in Chapter YII, there is a re- 

 turn migration toward the breeding-grounds of the immediate parents. 



In the more western and northern parts of the locust region, east of 

 the mountains, as in Minnesota, Dakota, and Colorado, the direction of 

 the departing swarms will be less constant, and according as they de- 

 velop late, or are the progeny of swarms that came from other directions 

 than the northwest, they will either be carried by the wind or will in- 

 stinctively leave in other directions. 



DESTINATION OF THE DEPARTING SWARMS. 



What eventually becomes of the insects which thus wend their way 

 on the wing toward the northwest in early summer *? W^hither do they 

 go ? These are questions constantly asked by people in the locust re- 

 gion. The history of the return flights of !I875 shows conclusively that 

 those insects which were healthy and vigorous enough to sustain long 

 flight, reached what we have termed the permanent breeding-grounds. 

 The records as given in Mr. Riley's Eighth Report clearly prove that they 

 reached into Northwest Dakota, Wyoming, and Montana, and the fol- 

 lowing passage from an article by Prof. G. M. Dawson in the Canadian 

 Naturalist, on the movements of locusts that year, gives the points 

 which they reached north of the boundary line: 



Foreign swarms from the south crossed the 49th parallel with a wide front stretching 

 from the 98th to the 108th meridian, and are quite distinguishable from those pro- 

 duced in the country, from the fact that many of them arrived before the latter were 

 mature. These flights constituted the extreme northern part of the army returning 

 northward and northwestward from the States ravaged in the autumn of 1874. They 

 appeared at Fort Ellice on the 13th of June, and at Qu'Appelle Fort on the 17th of 

 the same month, favored much, no doubt, by the steady south and southeast winds, 

 which, according to the meteorological register at Winnipeg, prevailed on the 12th of 

 June and for about a week thereafter. After their first appearance, however, their sub- 

 sequent progress seems to have been comparatively slow, and their advancing border 

 very irregular in outline. They are said to have reached Swan Lake House — the most 

 northerly point to which they are known to have attained — about July 10; while Fort 

 Pelly, farther west, and nearly a degree farther south, was reached July 20th, and 

 about seven days were occupied in the journey from there to Swan River Barracks, a 

 distance of only ten miles. 



In 1877, as is shown in Chapter YII, the northward flight seems to 

 have been less persistent toward the boundary line, and while there is 



