1933 ] 
Migratory Flight of Catopsilia euhule 
131 
A MIGRATORY FLIGHT OF CATOPSILIA EUBULE 
(LEPID.: PIERIDJE). 
By Harold O’Byrne 
Webster Groves, Missouri 
The butterflies belonging to the genus Catopsilia are fre- 
quent migrants, and many records of their migratory 
flights have been published. But these records are often 
vague as to the identity of the species, or they lack the 
precise data necessary to explain the problems that arise 
in connection with migratory behavior. 
During September and early October of 1932, the writer 
has had an opportunity to witness a migratory flight of 
Catopsilia eubule L. which was in progress over a large 
part of St. Louis County, Missouri. Most of the observa- 
tions were made at Webster Groves, but the flight was also 
seen in various other places. It was first noticed on Septem- 
ber 3rd, and had probably already been going on for some 
time. The butterflies were flying almost due south (their 
direction being only a few degrees to the east) during the 
hours when butterflies are usually active, and on days when 
weather conditions were favorable to butterfly activity. On 
cool or cloudy days, as well as during the early morning 
hours, few or none were to be seen. They were most nu- 
merous between 10 A. M. and 3 P. M. The direction of the 
wind did not influence their flight. This was always in a 
southward direction although the prevailing winds were 
from the west and northwest. They flew from two to ten 
feet from the ground with an average of about five or six 
feet. Both sexes were observed in the movement. 
Mr. Stuart L. O’Byrne, brother of the writer, made 
counts to determine the frequency with which the butter- 
flies passed between him and a point approximately 100 
feet east of his position, and the results are shown in the 
accompanying table. As already stated, all the butterflies 
