12 Dragon-Flies : their Life- History. [Sess. 



frequently appear in seasons of prolonged drought, when all the marshes 

 and water-courses 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 simultane- 

 ously 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 dragon-fly 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 Eae and other observers, perform long journeys north and south at 

 regular seasons, " from a sense of polarity." Neither this hypothetical 

 sense in animals nor " historical memory " will account for the dragon-fly 

 storms, as the phenomenon of the pampas might be called, since the insects 

 do not pass and repass between "breeding and subsistence areas," but all 

 journey in a north-easterly direction ; and of the countless millions flying 

 like thistle-down before the great pampero wind, not one solitary traveller 

 ever returns. 



The cause of the flight is probably dynamical, affecting the insects with 

 a sudden panic, and compelling them to rush away before the approaching 

 tempest. The mystery is that they should fly from the wind before it 

 reaches them, and yet travel in the same direction with it. When they 

 pass over the level, treeless country not one insect lags behind, or permits 

 the wind to overtake it ; but, on arriving at a wood or large plantation, 

 they swarm into it, as if seeking shelter from some swift-pursuing enemy, 

 and on such occasions they sometimes remain clinging to the trees while 

 the wind spends its force. This is particularly the case when the wind 

 blows up at a late hour of the day ; then on the following morning the 

 dragon-flies are seen clustering to the foliage in such numbers that many 

 trees are covered with them, a large tree often appearing as if hung with 

 curtains of some brown glistening material, too thick to show the green 

 leaves beneath. 



In Patagonia, where the phenomenon of dragon-fly storms is also known, 

 an Englishman residing at the Eio Negro related to me the following occur- 

 rence which he witnessed there. A race-meeting was being held near the 

 town of El Carmen, on a high exposed piece of ground, when, shortly before 

 sunset, a violent pampero wind came up, laden with dense dust-clouds. A 

 few moments before the storm broke, the air all at once became obscured 



