XVII] BIONOMICS, ETC. 333 



suffered greatly, and soon died. The Dragonflies known to inhabit 

 brackish water are (as might be expected) certain species of 

 Libellulinae, Anax, and some Agrioninae; to which we may add, 

 in Australia, a few species of Austrolestes. 



Hibernation. 



In Europe, only one small Dragonfly (Sympycna fused) passes 

 the winter in the imaginal state. On warm days it may come out 

 and fly about, but it spends most of the time hiding away under 

 dead leaves. In Sydney, where the winter is mild and short, 

 both Diplacodes bipunctata and Austrolestes leda hibernate regularly 

 through June, July and the early part of August. On sunny 

 days in those months, I have occasionally found them flying. 



Migration. 



As Dragonflies are frequently seen and even captured far from 

 land, it has been assumed that the Odonata as a whole are readily 

 dispersed, and overcome natural barriers with great ease. The 

 evidence does not, however, warrant this. Dragonflies quickly 

 take cover when bad weather is at hand, and are seldom likely 

 to be caught in a storm or driven out to sea. The only species 

 that are at all liable to spread are those with strong migratory 

 instincts. Of these, Libellula quadrimaculata is the most con- 

 spicuous example. Immense swarms of this species have been 

 recorded in different parts of Europe on many occasions. These 

 swarms sometimes pass out to sea, and may travel hundreds of 

 miles. A few large Aeschninae sometimes accompany them. 

 In Australia, Hemicordulia tau occasionally swarms in like manner, 

 and appears to travel a long distance, though not yet recorded 

 at sea. It has, however, recently colonized Tasmania, across 

 a strait two hundred miles wide ! On the other hand, the strong- 

 flying and equally common Anax papuensis has so far failed to do 

 this. Pantala flavescens and some species of Tramea travel far 

 and wide, and have overspread the whole of the Tropics. Apart 

 from these few examples, the migratory instinct is not developed 

 in Odonata. It may be safely stated that a very great majority 

 of the Order never travel far from their favourite haunts, and are 

 as strongly "held" by natural barriers as are many insects of 

 much weaker flight. 



