1914.] 181 



THE GEOGRAPHICAL DISTRIBUTION OF DANAIDA PLEXIPPUS, L. 



(DANAIS ARCHIPPUS, P.) WITH ESPECIAL REFERENCE 



TO ITS RECENT MIGRATIONS. 



BY JAMES J. WALKER, M.A., R.N., F.L.S. 



In a former volume of this Magazine (Ent. Mo. Mag., vol. XXII, 

 pp. 217-224), shortly after the capture of a considerable number of 

 specimens of Danaida plexippus in Britain had been recorded in our 

 current Entomological periodicals, I was induced to publish some notes 

 on this most interesting butterfly embodying my observations made 

 during a voyage in H.M.S. "Kingfisher" in the Eastern and Central 

 Pacific Ocean, and to speculate on the probable causes of the rapid 

 spread of the species at that time taking place across the warmer parts 

 of that ocean and the Atlantic. In the long interval that has elapsed 

 since this paper was written, two more voyages to Australia and the 

 Western Pacific, where the butterfly has now presumably established 

 itself as a permanent member of the insect fauna of these regions, 

 have enabled me to add very materially to my experiences on the subject 

 of the life-history and the wanderings of D. plexipptis. I therefore 

 venture to submit to the readers of this Magazine a summary of the 

 history of the recent wonderful extension of its geographical range, in 

 the hope that a useful purpose will be served in bringing together the 

 scattered records of many observers during the last half-century or 

 more, and that these records will prove to be of interest to 

 Entomologists in general. 



Although up to a very recent date Danaida plexippus — to give the 

 butterfly its most recent generic name as adopted by Dr. Karl Jordan 

 and Prof. E. B. Poulton — has been regarded as an undoubted native 

 of the New World, the evidence brought forward by the last-named 

 distinguished Entomologist (Trans. Ent. Soc. Lond., 1908, pp. 449-452 : 

 Charles Darwin and the Origin of Species, pp. 152-164, 204 [1909]) 

 appears, to myself at any rate, to be conclusive that so far from this 

 being the case, it is really " a member of an Old World genus that has 

 invaded the New." Its striking dissimilarity from all but a very few 

 (obviously allied) forms of the multitude of American Danaine butter- 

 flies, and its equally striking resemblance in all its stages to the widely 

 distributed and abundant Oriental D. genutia, Cram., had, it is true, 

 not escaped notice previous to the appearance of Prof. Poulton' s paper ; 

 but I cannot do better than to quote the learned Professor's own words 

 in his masterly essay on " Mimicry in North American Butterflies " 

 (Darwin and the Origin of Species, pp. 159-160). " The suggestion 



