THE MIGRATION OP BUTTERFLIES. 34 1 



place, leading to a compensating reduction of the species after a 

 season exceptionally favourable to its increase. In this view 

 Col. Swinhoe, whose extensive acquaintance with the Lepi- 

 doptera of India and Ceylon is well known, has expressed his 

 concurrence. But since these remarks were made, some additional 

 and most interesting information has come to light, and from an 

 unexpected source. Herr Gatke, who for fifty years has devoted 

 himself to a study of the migratory birds which visit Heligoland, 

 has published, in a bulky volume, the results of his observations, 

 and an English translation of the German text has just been 

 issued.* In this volume will be found some extremely interesting 

 observations on the migration of butterflies, from which the 

 following is an extract : — 



" That Lepidoptera during their more extended flights are 

 subject to the same meteorological influences as birds, I have 

 been convinced by the experience of many nights in July, during 

 which I have caught numerous nocturnal Lepidoptera not belong- 

 ing to our insect-fauna, the weather of these nights being invariably 

 such that, if it had occurred a few weeks later, it would have con- 

 ducted hither innumerable Wheatears. It has, in fact, occurred 

 repeatedly that Lepidoptera, especially night-flying species, have 

 passed over this island in countless swarms at the time of powerful 

 bird-migrations. Thus, during the night of the 25th of October, 

 1872, thousands of Hybernia defoliaria, mixed with smaller 

 numbers of H. aurantiaria, passed over the island in the com- 

 pany of large numbers of Larks. And again, in the night of 

 the 11th of October, 1883, during which an unusually strong 

 migration of all the species of birds due at that time took place, 

 this was accompanied by the appearance of very large swarms of 

 the same species of Hybernia. 



"White Cabbage Butterflies, the Black Arches, Psilura 

 monacha, and also Libellulidce (Libellida quadripunctata) have 

 been seen to pass here in migratory flights of astonishing 

 proportions, though even these do not come up to those of 

 Plusia gamma, which on repeated occasions have occurred in 

 numbers of which it would be quite impossible to form any 



* ' Heligoland as an Ornithological Observatory : the result of fifty years' 

 experience by Heinrich Gatke.' Translated by Rudolph Rosenstock. Roy. 8vo. 

 Edinburgh ; David Douglas. 1895. 



