so familiar on the pampas, and which, strangely enough, has not been
recorded by any European naturalists who have travelled there.




CHAPTER X.

MOSQUITOES AND PARASITE PROBLEMS.


There cannot be a doubt that some animals possess an instinctive
knowledge of their enemies--or, at all events, of some of their
enemies--though I do not believe that this faculty is so common as many
naturalists imagine. The most striking example I am acquainted with is
seen in gnats or mosquitoes, and in the minute South American sandflies
(Simulia), when a dragon-fly appears in a place where they are holding
their aerial pastimes. The sudden appearance of a ghost among human
revellers could not produce a greater panic. I have spoken in the last
chapter of periodical storms or waves of dragon-flies in the Plata
region, and mentioned incidentally that the appearance of these insects
is most welcome in oppressively hot weather, since they are known to
come just in advance of a rush of cool wind. In La Plata we also look
for the dragon-fly, and rejoice at its coming, for another reason. We
know that the presence of this noble insect will cause the clouds of
stinging gnats and flies, which make life a burden, to vanish like
smoke.

When a flight of dragon-flies passes over the country many remain along
the route, as I have said, sheltering themselves wherever trees occur;