1833.J A SHOWER OF BUTTERFLIES. 163 



should be recollected with gratitude by those who have 

 visited Spanish South America. 



December ^th. — The Beagle sailed from the Rio Plata, 

 never again to enter its muddy stream. Our course was 

 directed to Port Desire, on the coast oF Patagonia. Before 

 proceeding any further, I will here put together a few 

 observations made at sea. 



Several times when the ship has been some miles off the 

 mouth of the Plata, and at other times when off the shores 

 of Northern Patagonia, we have been surrounded by insects. 

 One evening, when we were about ten miles from the Bay 

 of San Bias, 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 the 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 great number 

 of the Carahidce 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. 1 

 lost some of the specimens, but those which I preserved 

 belonged to the genera Colymbetes, Hydroporus, rJydrotnus 



* Lyell't " Principle! of Geology," vol. m., p. 63. 



