OF WASHINGTON. 257 
males during the mating season approach each other from a long dis- 
tance, as could be observed easily on the prairies. As soon as they came 
within ten feet of each other they would immediately cease the chase- 
Evidently in this case each male had been notified by the odor produced 
in the pockets of the other that the desired interview would prove futile 
and useless. Two females, on the contrary, would chase each other for 
a very long time before reaching the same conclusion. As soon as the 
males recognized each other they invariably would fly away in different 
directions, and only by the use of a gun could they be captured and their 
sex ascertained. 
The butterflies, in migrating south, do not fly singly, but in large num- 
bers and together. Like swallows, they gather every night for several 
weeks in certain localities, and after thus becoming accustomed to swarm 
together, they utilize the first favorable wind to start upon their journey. 
On August 17, 1888, I found such a swarm near Detroit, Minn., and ob- 
served more closely another one near Battle Lake a few days later. To 
study their motions, I camped for several days in this locality, which is a 
little grove of poplars near a very small creek. During the day but few- 
butterflies could be seen flying about in search of food. But towards sun- 
set large numbers of them came from all points of the compass ;md settled 
upon the trees, selecting the crowns. As long as I could see, butterflies 
arrived, and millions of them must have crowded together. Early in the 
morning the butterflies commenced to leave this grove, not singly, but in 
large numbers, which broke up into smaller companies to scatter over the 
prairies in search of food. In this instance I am sure that the butterflies 
met every evening for at least ten days, but very likely for a longer period, 
as the wind during the period was from the south. With the first wind 
from the north all had disappeared. 
I also observed their motions at St. Anthony Park, but in this case they 
were already upon their southward journey. During some days with a 
wind blowing from the north, the air was filled with such butterflies. 
None flew at a distance above ground less than 250 feet, most of them very 
much higher. A good field-glass revealed large numbers at a much greater 
altitude, barely visible as mere spots with this instrument. Nor did the 
butterflies really fly, but they drifted or sailed along very rapidly with the 
wind. Their wings were fully extended in an almost horizontal position, 
and the insects seemed to use them only from time to time to keep their 
heads in the proper forward position. They flew both during the night 
and during the day. As soon as the wind changed its course all butterflies 
descended; it " rained butterflies," as my little boy called this phenom- 
enon. Where no butterflies could be found for several weeks, everything 
was now alive with them. With their powerful wings they could be seen 
flying about everywhere, but I did not see a single specimen take food, 
although numerous thistles invited them. Sometimes the currents in 
higher layers of the air were in their favor, whilst those below were not. 
High in the air numerous butterflies sailed by, but those near the surface 
