Mosquitoes and Parasite Problems. 137 



with a pertinacious cloud of gnats or sandflies 

 hovering just above my head and keeping me 

 company for miles, I have always devoutly wished 

 for a stray dragon-fly to show himself. Frequently 

 the wish has been fulfilled, the dragon-fly, appa- 

 rently " sagacious of his quarry from afar," sweeping 

 straight at his prey, and instantly, as if by miracle, 

 the stinging rain has ceased and the noxious cloud 

 vanished from overhead, to be re-formed no more. 

 This has always seemed very extraordinary to me ; 

 for in other matters gnats do not appear to possess 

 even that proverbial small dose of intellect for which 

 we give most insects credit. Before the advent of 

 the dragon-fly it has perhaps happened that I have 

 been vigorously striking at them, making it very 

 unpleasant for them, and also killing and disabling 

 many hundreds a larger number than the most 

 voracious dragon-fly could devour in the course of 

 a whole day ; and yet, after brushing and beating 

 them off until my arms have ached with the exer- 

 tion, they have continued to rush blindly on their 

 fate, exhibiting not the faintest symptom of fear. 

 I suppose that for centuries mosquitoes have, in this 

 way, been brushed and beaten away with hands and 

 with tails, without learning caution. It is not in 

 their knowledge that there are hands and tails. A 

 large animal is simply a field on which they con- 

 fidently settle to feed, sounding shrill flourishes on 

 their little trumpets to show how fearless they are. 

 But the dragon-fly is very ancient on the earbh, and 

 if, during the Devonian epoch, when it existed, it 

 preyed on some blood-sucking insect from which 

 our Culicidse have come, then these stupid little 



