distributed insects, being three inches to four inches in length, and as
a rule they are sober-coloured, although there is one species--the
largest among them--entirely of a brilliant scarlet. This kind is,
however, exceedingly rare. All the different kinds (of the large
dragon-flies) when travelling associate together, and occasionally, in a
flight composed of countless thousands, one of these brilliant-hued
individuals will catch the eye, appearing as conspicuous among the
others as a poppy or scarlet geranium growing alone in an otherwise
flowerless field. The most common species--and in some cases the entire
flight seems to be composed of this kind only--is the Aeschna
bonariensis Raml, the prevailing colour of which is pale blue. But the
really wonderful thing about them all alike is, that they appear only
when flying before the southwest wind, called _pampero_--the wind that
blows from the interior of the pampas. The pampero is a dry, cold wind,
exceedingly violent. It bursts on the plains very suddenly, and usually
lasts only a short time, sometimes not more than ten minutes; it comes
irregularly, and at all seasons of the year, but is most frequent in the
hot season, and after exceptionally sultry weather. 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