INSECT MIGRATION 1 5 



had seen did stop at the grove. Apparently this is a regular and well 

 recognized resting point with the migrating insects. 



I traced this course of flight several miles northwest and also 

 about seven miles to the southeast of Charles City. It is well 

 defined and as shown, is used by large numbers of insects. It 

 is, however merely a local element of a larger route that roughly 

 passes across almost the full widths of Floyd and Cerro Cordo 

 Counties. 



In 1 91 7 the Monarch migration began in the latter part of 

 August, although the Sulphur migration did not commence until 

 about the middle of September. On August 30, I observed a 

 large and continuous flight of Monarchs at a point in the east- 

 central portion of Cerro Gordo County. Here the butterflies 

 skirted the lower portion of a seventy-foot bluff and at that point 

 were flying almost due east but further investigation showed that 

 as soon as this chain of hills disappeared the flight turned to the 

 southeast. The next day I observed large numbers of Monarchs 

 and Clover Sulphurs at a point about eight miles to the southeast 

 of the point where I had noted the flight on the day before. It 

 is notable that while this line of flight is some miles to the west of 

 the one first described, it has the same general direction, both follow- 

 ing the general trend of stream flow. 



At Charles City there were large numbers of migrating Monarchs 

 on September 5, but the migration reached its height from the 

 twelfth to the fifteenth, and on these latter days a considerable 

 percentage of C alias was found in the flocks studied. At no time 

 was Pieris rapae noted in any of the flocks, though the species 

 was fully as abundant as usual. 



In none of the migrations have there been any indications that 

 the same routes were used by birds or other insects, as for instance 

 the dragonflies. Neither was any point noted where the path of 

 migration became extremely narrow. In the spring, usually about 

 the first of June, a few battered and weatherworn Monarchs appear, 

 but there is no return of the Sulphurs. The Mourning Cloaks 

 {Vanessa antiopa) often is found, in hibernated specimens, as early 

 as April i, and thus appears to be the earliest of the butterflies 

 of that vicinity. 



The accompanying sketch-map gives the two main routes of 

 butterfly migration in Floyd and Cerro Gordo Counties, as indi 

 cated by these studies. 



