172 CHARLES DARWIN 



December 6th. 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 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 be- 

 longed to a kind very similar to, but not identical with, the 

 common English Colias edusa. Some moths and hymenop- 

 tera accompanied the butterflies; and a fine beetle (Calo- 

 soma) 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 Carabidae 

 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; 5 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 Cor- 

 rientes, 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 spe- 



8 Lyell's Principles of Geology, vol. iii. p. 63. 



