KELATION OF TEMPERATURE, ETC., TO LOCUST FLIGHTS. 155 
The best way in which we can show the relation between the flights 
and the temperature and wind, is to compare statements in our First 
Eeport with this table, which was made out after the report was printed ; 
all the statements relate to 1877. 
At page 172 it is stated that the first flight observed in Iowa was June 
14, from the south, aud that the locusts came down in the vicinity of Sioux 
City, in the extreme northwest part, where they remained some days. By 
reference to the Yankton column, it appears that the temperature rose on 
the 13th and 14th, and fell again on the 15th; the wind was from the 
north until the 14th, when it changed and blew from the south, wheeling 
again in the evening to the north. On the 16th it was again from the 
south, and the temperature again rose, and this condition continued 
through the 17th. By reference to page 173, it will be seen there was a 
heavy flight northward across the southeastern counties of Dakota. 
This is one out of hundreds of similar cases which show not only the re- 
lation between the temperature and flights, but that the locusts are not 
easily turned back by adverse winds when they start in a given direc- 
tion — though in 1877 this was not so marked as is usually the case. In- 
vading swarms from the permanent breeding grounds will come down 
and remain for days waiting for the wind to blow in the right direction, 
and seldom, if ever, are turned back. With local flights, to which cate- 
gory those of 1877 chiefly belong, the case is different. The fall in tem- 
perature has much to do with their coming down, as in the case just 
given, as we find that afterwards those which went northward did gen- 
erally return southward in 1877 ; but the case was different in 1876. 
From July 2 to 7 the weather was excessively warm, as will be seen 
by reference to the records for Yankton and North Platte, and the direc- 
tion of the wind was west or northwest. By turning to the record of 
flights for 1877 (appendix, 168-173), it will be seen that these were the 
days of the great flights to the west and northwest, the air being full of 
locusts over Minnesota, Northern Iowa, Dakota, and Nebraska. 
Page 174: " July 8. — Swarms returning, moving generally a little east 
of south." Compare this, which applies to Minnesota and Dakota, with 
records of Bismarck, Yankton, and North Platte for July 8. 
It is unnecessary for us to add more illustrations, as the readers can 
compare the records of flights as given in our First Report with this 
meteorological table for themselves. It appears from a careful com- 
parison of this kind that whenever the maximum temperature falls be- 
low 70° and the minimum below 60° that there is no flying. See for 
illustration the records of flights, July 18 and 19, appendix, p. [182], 
so far as it relates to Dakota, and compare with the Bismarck record in 
the table for the same dates. 
