EHOPALOCERA. 31 



is common to see a female " mobbed " (as Professor Moseley says of 

 the magnificent Ornithoptera Poseidon in the Am 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 Danaincc ^ and Acrceince, butterflies in 

 general do not exhibit a sociable or gregarious disposition. There are, 

 however, extraordinary assemblages of Pierince, which, in South 

 America especially, have been recorded by many observers, including 

 Darwin, Wallace, Bates, and E. 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. Pesearches Hat. 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 Pdusa." 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 Pierince 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 larv« 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. Lond., 

 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 calm 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. 



