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 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.
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