und in South
America. They must have come, therefore, from the Cape Verde Islands, or
from some parts of the African coast, and must have traversed about a
thousand miles of ocean with the assistance, no doubt, of a strong
north-east trade wind for a great part of the distance. In the British
Museum collection there is a specimen of the same moth caught at sea
during the voyage of the _Rattlesnake_, in Lat. 6 deg. N., Long. 22-1/2 deg.
W., being between the former position and Sierra Leone, thus rendering
it probable that the moths came from that part of the African coast, in
which case the swarm encountered by the _Pleione_ must have travelled
more than 1200 miles.

A similar case was recorded by Mr. F.A. Lucas in the American periodical
_Science_ of 8th April 1887. He states that in 1870 he met with numerous
moths of many species while at sea in the South Atlantic (Lat. 25 deg. S.,
Long. 24 deg. W.), about 1000 miles from the coast of Brazil. As this
position is just beyond the south-east trades, the insects may have been
brought from the land by a westerly gale. In the _Zoologist_ (1864, p.
8920) is the record of a small longicorn beetle which flew on board a
ship 500 miles off the west coast of Africa. Numerous other cases are
recorded of insects at less distances from land, and, taken in
connection with those already given, they are sufficient to show that
great numbers must be continually carried out to sea, and that
occasionally they are able to reach enormous distances. But the
reproductive powers of insects are so great that all we require, in
order to stock a remote island, is that some few specimens shall reach
it even once in a century, or once in a thousand years.

_Insects at great Altitudes._

Equally important is the proof we possess that insects are often carried
to great altitudes by upward currents of air. Humboldt noticed them up
to heights of 15,000 and 18,000 feet in South America, and Mr. Albert
Mueller has collected many interesting cases of the same character in
Europe.[173] A moth (Plusia gamma) has been found on the summit of Mont
Blanc; small hymenoptera and moths have been seen on the Pyrenees at a
height of 11,000 feet, while numerous flies and beetles, some of
considerable size, have been caught on the glaciers and snow-fields of
various parts of the Alps. Upward currents of air, whirlwinds and
tornadoes, occur in all parts of the world, and large numbers of insects
are thus carried u