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 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 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 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 of 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. [6]
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 was sixty miles distant from the land, in the
direction of a steady though light breeze. Vast numbers of a small
spider, about one-tenth of an inch in length, and of a dusky red
colour, were attached to the webs. There must have been, I should
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