THE CANADIAN ENTOMOLOGIST. 219 



A SUPPOSED MIGRATION OF PIERID.E WITNESSED IN 

 VENEZUELA IN THE SUMMER OF igor. 



BY AUSTIN H. CLARK, HARVARD UNIVERSITY, CAMBRIDGE, MASS. 



The erratic migrations of certain insects, often in countless swarms, 

 have been noticed and put on record by many observers. In a country 

 where, perhaps, they are scarce, or, it may be, almost wanting ordinarily, 

 they may suddenly put in an appearance in such numbers as to defy all 

 attempts at computation ; or immense swarms of them may sometimes be 

 seen far out at sea, flying steadily in a direction which may take them out 

 so far as to effectually prevent any return. 



To show the frequency of this phenomenon, it is only necessary to 

 mention a few cases. The best known, perhaps, or, at any rate, the most 

 familiar, is that of the locust. Large areas of growing crops have been 

 totally ruined and well-to-do people reduced to poverty through the 

 sudden and wholly unexpected appearance of this unwelcome visitor. 

 Many years may pass with no sign of these insects, and then they come, 

 bringing destruction with them. Among the Neuroptera, the dragon-flies, 

 especially the species JEschna bonariensis of southern South America, seem 

 to be especially subject to these migrations. In these swarms, according 

 to Hudson,* who studied them in the Argentine, all the larger species 

 associate together, and universally fly down the wind, coming commonly 

 from five to fifteen minutes before a burst of the cold, dry south-west 

 " pampero." Weissenbornf describes a great migration of dragon-flies 

 which he witnessed in Germany in the year 1839, and also mentions a 

 similar phenomenon occurring in 1816, which extended over a large 

 portion of Europe. But this habit seems to be of commonest occurrence 

 among the Lepidoptera. Among others, Wallace mentions seeing a vast 

 congregation of Pieridae in the Indian Ocean, and Maynard a swarm of 

 Danaidpe f'/^/zfj/a ^^r^;2?V^j off the coast of Florida. It is now recognized 

 as a more or less regular proceeding on the part of some species or 

 groups, especially among the Pieridae, to congregate and perform long 

 journeys without any apparent aim. 



While approaching the coast of Venezuela in the month of June, 

 1 90 1, I was struck by the numbers of Pieridas passed, not in great swarms, 

 but in numerous small loose bunches, which began to appear even before 

 the mountainous coast could be well made out. All these insects were 



*The iVaturalist on the La Plata, Chapter IX. 

 fLoudon's Magazine of Natural History, N. S. III. 



