1833.] FLOCKS OF BUTTERFLIES. 159 



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 in- 

 jured by the salt water. I lost some of the specimens, but those 

 which I preserved belonged to the genera Colymbetes, Hydropo- 

 rus, Hydrobius (two species), Notaphus, Cynucus, Adimonia, and 

 Scarabaeus. At first I thought 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 ap- 

 peared 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 Adventure. The cause 

 })robably is due to the want of shelter, both of trees and hills, so 

 that an insect on the wing, with an off-shore breeze, would be 

 very apt to be blown out to sea. The most remarkable instance 

 I have known of an insect being caught far from the land, was 

 tliat of a large grasshopper (Acrydium), which flew on board, 

 when the Beagle was to v.indward of the Cape de Yerd Islands, 

 and when the nearest point of land, not directly opposed to the 

 trade-wind, was Cape Blanco on the coast of Africa, 370 miles 

 distant.* 



On several occasions, when the Beagle has been within the 

 mouth of the Plata, the rigging has been coated with the web of 

 the Gossamer Spider. One day (November 1st, 1832) I paid 

 particular attention to this subject. The weather had been fine 

 and clear, and in the morning the air was full of patches of the 

 flocculent web, as on an autumnal day in England. The ship 



* The fiies -which frequently accompany a ship for some days on ita 

 passage from harbour to harbour, wandering from the vessel, are soon lost, 

 and all disappear. 



8 



