14 MONTANA EXPERIMENT STATION BULLETIN 366 



This large flight apparently originated in north-central 

 South Dakota and south-central North Dakota. Some of the grass- 

 hoppers flew through Montana and far into Saskatchewan. The 

 large migrations took place when the temperature was above 80° 

 and a southerly wind was blowing. Interesting information bear- 

 ing on this point is recorded by Munro and Saugstad in the Bi- 

 monthly Bulletin of the North Dakota Agricultural Experiment 

 Station, Volume 1, Number 1, 1938: 



"The direction of dispersal has ranged from north to northwest from 

 the point of release. A possible explanation of this may be that winds 

 from the south and southeast, being warmer than those from other di- 

 rections, were more effective in promoting sustained flights of the in- 

 sects. Records of the United States Weather Bureau reveal that for 15 

 days of the 29-day period, begnning July 17, winds from the south and 

 southeast prevailed with an average daily maximum temperature of 

 88.9° F. For the remaining 11 days, which included 7 in July and 4 in 

 August, the winds from the north and northwest prevailed with an 

 average daily maximum temperature of 79° F. — a difference of 9.9° F. 

 lower than the warmer winds from the south. The velocity of the 

 southern winds averaged 7.04 miles per hour while those from the 

 northerly direction averaged 8.1 miles. The heavy flights were gener- 

 ally observed to be travelling with the prevailing winds from the south." 



While this temperature difference is doubtless of much im- 

 portance, it was noticed on several occasions on July 12th and 

 13th in eastern Montana, that occasional 'hoppers rose some dis- 

 tance into the air and attempted to fly to the northwest, against 

 the wind. 



The flights in eastern Montana during the height of the in- 

 vasion did not appear to be general over the whole area but 

 took the form of large irregular clouds. The maximum eleva- 

 tion at which the migrating grasshoppers flew was not deter- 

 mined, but the following excerpt from a letter received from 

 Mr. M. B. Freeburg, Superintendent of the Eastern Division of 

 the Northwest Airlines, and dated September 1, 1938, is of 

 interest: 



"On July 27, I encountered a large concentrated flight of 'hoppers 

 immediately east of Billings at approximately 7000 feet. It was ap- 

 proximately three miles through the flight Mr. Peterson at 



Billings reports that our Flight 2 of the 26th encountered a flight of 

 'hoppers at 11,000 feet between Helena and Billings. This is the only 

 accurate and exact information I can give you at the moment, although 

 I might mention that over a period of years 'hopper flights have been 



