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 
Scarabeus. 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 Jand. 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 
probably 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 
that of a large grasshopper (Acrydium), which flew on board, 
when the Beagle was to windward of the Cape de Verd 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 Ist, 1882) 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 flies which frequently accompany a ship for some days on its 
‘passage from harbour to harbour, wandering from the vessel, are soon lost, 
and all disappear. 
8 
