154 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



Yellowstone and its tributaries, the Big Horn Eiver, Powder Eiver, 

 North Fork of the Big Cheyenne, which drain the larger part of the 

 Territory- of Wyoming, is shown by the observations of Lieutenant Car- 

 penter, United States Army, communicated to the Commission. The 

 source of the swarms that invaded the States lying east of the 103d 

 meridian is clearly shown to have been mainly from Eastern Montana,^^ 

 and the region lying north up to the North Saskatchewan, and the 

 northern half of Wyoming. 



On the other hand. Eastern Montana was visited in 1875, and again 

 in 1877, by large swarms from the east and southeast, and these again 

 were evidently the locusts which bred in the States east of the 103d 

 meridian in 1875 and 1877, from eggs laid in those States by the locusts 

 which invaded them in 1874 and again in 1876. 



For example, at Fort Shaw large swarms which were much more de- 

 structive than the local swarms seen in 1873 and 1874 were from the 

 east, and, from information received at Fort Benton, a large area of East- 

 ern Montana was invaded by locusts which must have come from the 

 southeast of the Territory, and most probably were in large part return 

 swarms from the border States. 



While the general movement at Forts Benton and Peck on the Mis- 

 souri Eiver in 1876 was eastward and southeastward, locusts were ob- 

 served at both points flying from the southeast and east j these may 

 have been of local origin. 



In 1877 the locusts fle.w from the east at Fort Peck June 20. These had 

 evidently come from Minnesota. These are not to be confounded with 

 the swarms that arrived August 13 and 14. At this date moderate 

 swarms arrived from the east-southeast. Mr. O. O. Martson writes that 

 ''they were previously heard of 90 miles south of Fort Benton coming 

 from the east. The swarms which visited Fort Benton the middle of 

 August were probably an offshoot from the large swarms which arrived 

 about that time south of us about 100 miles, the mountain-ranges having 

 separated them.^^ These swarms were probably those which invaded 

 the Gallatin Valley and originated in the bad lands of the Yellowstone. 



At Helena the locusts, so far as observed, arrived from the east over 

 the Belt Mountains, from the direction of the Yellowstone Eiver. On 

 the other hand, at Deer Lodge Mr. Granville Stuart informs us that, 

 while the prevailing winds are west and northwest, the locusts always 

 come with north and northeast winds j these would bring them from the 

 Sun Eiver Valley (Fort Shaw). 



The Lower Missoula Valley, lying west of Helena and Deer Lodge, was 

 invaded in 186G by swarms from the north and northeast and east, some 

 passing apparently from British America down the Flathead Eiver and 

 over the Eocky Mountain divide in August. None were seen afterward 

 from 1868-1874. 



In 1875 another invasion, as Mr. Chauncey Barbour informs us, came 



22 ifiimely, that portion of Montana lying north of latitude 45°, and tast of longitude 11J°. 



