EHOPALOCERA. 
31 
is common to see a female " mobbed " (as Professor Moseley says of 
the magnificent Ornithoptera Poseidon in the Aru Islands) by many 
competing males ; and in the case of many Satyrince which frequent 
open ground, and whose sexes have the same habits, the females are 
unquestionably much the scarcer. 
With the exception of the Danainm ^ and Acrminm^ butterflies in 
general do not exhibit a sociable or gregarious disposition. There are, 
however, extraordinary assemblages of Fierince, which, in South 
America especially, have been recorded by many observers, including 
Darwin, Wallace, Bates, and K. Spruce. The innumerable multitudes 
on the wing in some of these swarms may be imagined from Darwin's 
often-quoted account of his experience when in the Beagle " off the 
South American coast. He writes (Journ. Researches Nat. Hist.^ &c., 
new edit., 1870, p. 158): ''Vast numbers of butterflies, in bands or 
flocks of countless myriads, extended as far as the eye could range. 
Even by the aid of a telescope it was not possible to see a space free 
from butterflies. . . . More species than one were present, but the main 
part belonged to a kind very similar to, but not identical with, the 
common English Colias Udusa." Mr. Bates, too, describes a flight of 
butterflies across the Amazon- which lasted for two days without inter- 
mission during the hours of daylight ; and in this case nearly all were 
species of Callidryas, swift-flying Pierinm allied to Colias, and, as far 
as the observer could ascertain, the swarms consisted exclusively of 
males. Mr. Spruce {Journ. Linn. Soc., ZooL, ix. pp. 355-357), in a 
most interesting paper on these migrations, points out that in South 
America their direction is always to the south, and attributes them as 
mainly due to the exhaustion of the food supply in seasons when the 
insects concerned are by rains and other favouring circumstances 
produced in certain districts in unwonted abundance. Mr. Spruce 
mentions a swarm near Guayaquil consisting of both butterflies and 
moths ; and in this case both sexes were concerned, as he noticed the 
females laying eggs, and saw the innumerable resulting larvge destroy 
the shore vegetation, leaving none for the hordes that continued to 
arrive, and that thereupon '' launched boldly out over the Pacific 
Ocean." As I have already put on record (Trans. Ent Soc. Zond., 
1870, p. 383), Colonel Bowker witnessed, in March 1869, an immense 
flight of Callidryas Florella, " all steadily moving on eastward " across 
the Maluti Mountains in Basutoland : in this swarm both sexes were 
represented, the females being easily recognised by being mostly yellow 
instead of greenish-white. Colonel Bowker mentioned that he had 
seen similar gatherings both in the Cape Colony and in the Trans-Keian 
^ In Moore's Lepidoptera of Ceylon, i. pp. i, 2 (1880), there is an interesting note by 
the late Dr. Thwaites on the " amazing numbers " of one or more species of Euploea which 
appear on fine cahn days, all flying together in the same direction. From the particulars 
mentioned, these Cingalese Danaince swarms seem to behave very similarly to the flights of- 
Pierince mentioned in the text. 
