J68 RIO PLATA chap. 



aid of a telescope it was not possible to see a space free from 

 butterflies. The seamen cried out " it was snowing butterflies," 

 and such in fact was the appearance. 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 edusa. 

 Some moths and hymenoptera accompanied the butterflies ; 

 and a fine beetle (Calosoma) flew on board. Other instances 

 are known of this beetle having been caught far out at sea ; and 

 this is the more remarkable, as the greater number of the 

 Carabidse seldom or never take wing. The day had been fine 

 and calm, and the one previous to it equally so, with light and 

 variable airs. Hence we cannot suppose that the insects were 

 blown off the land, but we must conclude that they voluntarily 

 took flight. The great bands of the Colias seem at first to 

 afford an instance like those on record of the migrations of 

 another butterfly, Vanessa cardui ; ^ but the presence of other 

 insects makes the case distinct, and even less intelligible. 

 Before sunset a strong breeze sprung up from the north, and 

 this must have caused tens of thousands of the butterflies and 

 other insects to have perished. 



On another occasion, when seventeen miles off Cape 

 Corrientes, I had a net overboard to catch pelagic animals. 

 Upon drawing it up, to my surprise I found a considerable 

 number of beetles in it, and although in the open sea, they did 

 not appear much injured by the salt water. I lost some of the 

 specimens, but those which I preserved belonged to the genera 

 Colymbetes, Hydroporus, Hydrobius (two species), Notaphus, 

 Cynucus, Adimonia, and Scarabasus. At first I thoojght that 

 these insects had been blown from the shore ; but upon reflecting 

 that out of the eight species four were aquatic, and two others 

 partly so in their habits, it appeared to me most probable that 

 they were floated into the sea by a small stream which drains a 

 lake near Cape Corrientes. On any supposition it is an 

 interesting circumstance to find live insects swimming in the 

 open ocean seventeen miles from the nearest point of land. 

 There are several accounts of insects having been blown off 

 the Patagonian shore. Captain Cook observed it, as did more 

 lately Captain King in the Adventtire. The cause probably is 

 due to the want of shelter, both of trees and hills, so that an 



' Lyell's Principles of Geology, vol. iii. p. 6j, 



