ain rare emergencies, causing unsocial species to become gregarious
and to venture sometimes even to cross the ocean.

The armies of locusts which darken the air in Africa, and traverse the
globe from Turkey to our southern counties in England, are well known to
all. When the western gales sweep over the Pampas they bear along with
them myriads of insects of various kinds. As a proof of the manner in
which species may be thus diffused, I may mention that when the Creole
frigate was lying in the outer roads off Buenos Ayres, in 1819, at the
distance of six miles from the land, her decks and rigging were suddenly
covered by thousands of flies and grains of sand. The sides of the
vessel had just received a fresh coat of paint, to which the insects
adhered in such numbers as to spot and disfigure the vessel, and to
render it necessary partially to renew the paint.[933] Captain W. H.
Smyth was obliged to repaint his vessel, the Adventure, in the
Mediterranean, from the same cause. He was on his way from Malta to
Tripoli, when a southern wind blowing from the coast of Africa, then one
hundred miles distant, drove such myriads of flies upon the fresh paint,
that not the smallest point was left unoccupied by insects.

To the southward of the river Plate, off Cape St. Antonio, and at the
distance of fifty miles from land, several large dragon-flies alighted
on the Adventure frigate, during Captain King's late expedition to the
Straits of Magellan. If the wind abates when insects are thus crossing
the sea, the most delicate species are not necessarily drowned; for many
can repose without sinking on the water. The slender long-legged tipulae
have been seen standing on the surface of the sea, when driven out far
from our coast, and took wing immediately on being approached.[934]
Exotic beetles are sometimes thrown on our shore, which revive after
having been long drenched in salt water; and the periodical appearance
of some conspicuous butterflies amongst us, after being unseen some for
five others for fifty years, has been ascribed, not without probability,
to the agency of the winds.

Inundations of rivers, observes Kirby, if they happen at any season
except in the depths of winter, always carry down a number of insects,
floating on the surface of bits of stick, weeds, &c.; so that when the
waters subside, the entomologist may generally reap a plentiful harvest.
In the dissemination, moreover, of these minute beings, as in that