It is in summer and
autumn that the large dragon-flies appear; not _with_ the wind, but--and
this is the most curious part of the matter--in advance of it; and
inasmuch as these insects are not seen in the country at other times,
and frequently appear in seasons of prolonged drought, when all the
marshes and watercourses for many hundreds of miles are dry, they must
of course traverse immense distances, flying before the wind at a speed
of seventy or eighty miles an hour. On some occasions they appear almost
simultaneously with the wind, going by like a flash, and instantly
disappearing from sight. You have scarcely time to see them before the
wind strikes you. As a rule, however, they make their appearance from
five to fifteen minutes before the wind strikes; and when they are in
great numbers the air, to a height of ten or twelve feet above the
surface of the ground, is all at once seen to be full of them, rushing
past with extraordinary velocity in a north-easterly direction. In very
oppressive weather, and when the swiftly advancing pampero brings no
moving mountains of mingled cloud and dust, and is consequently not
expected, the sudden apparition of the dragon-fly is a most welcome one,
for then an immediate burst of cold wind is confidently looked for. In
the expressive vernacular of the gauchos the large dragon-fly is called
_hijo del pampero_--son of the south-west wind.
It is clear that these great and frequent dragonfly movements are not
explicable on any current hypothesis regarding the annual migrations of
birds, the occasional migrations of butterflies, or the migrations of
some mammals, like the reindeer and buffalo of Arctic America, which,
according to Rae and other observers, perform long journeys north and
south at regular seasons, "from a sense of polarity.
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