CHAPTER X. 



MOSQUITOES AND PAEASITE 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 com- 

 mon 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 



