The South Australian Naturalist. 



NOTES ON THE FORMS AND HABITS OF AQUATIC 



INSECTS.— Part H. 



By Herbert M. Hale (South Australian Museum). 



After watching: the gorgeously-coloured dragon-flies hawking 

 mosquitoes while travelling at a speed of fifty miles an hour, it is 

 difficult to associate these creatures with the squat larvae, lying 

 partially buried in mud or coated with filth, in the nearest 

 stagnant water. Yet so it is ! But the immature form is no less 

 interesting than the adult; indeed, the modifications which 

 enable the insect to develop in a murky pool to its final winged 

 state of perfection are well worthy of our consideration. 



Dragon-flies insert their eggs in stems and leaves of aquatic 

 plants, drop them into the water, or plunge the tip of the 

 abdomen therein and deposit the ova below the surface ; the egg- 

 laying habits vary amongst different species. Towards the end 

 of October of last year, members of the South Australian 

 Aquarium Society visited Millbrook Reservoir. Many thousands 

 of dragon-flies were present, and it was noted that the smaller 

 demoiselles walked do-vsTi reeds and sticks into the water, and 

 descended to a couple of feet below the surface — presumably to 

 deposit eggs. Mr. E. Savage then remarked that he had observed 

 similar occurences in the River Murray, and had there seen other 

 species behave in this singular manner. 



Larvae of several kinds of dragon-flies are found in almost 

 any pond, and an examination of one or other of them will show 

 that it is efficiently fitted for a predaeeous life. The under lip 

 consists of a singular jointed arm, terminating in a pair of strong 

 and more or less jagged pincers ; this apparatus is known as the 

 mask, because when retracted it covers the mouth parts and 

 sometimes even hides the whole face. The mask has very various 

 forms, and in no two species is it identical in shape. (See figs, 

 lb, 2a, and 3a.) Living insects, including those of its own kind, 

 are captured by darting forward the lower lip and seizing the 

 victim in the pincers ; when its struggles lessen the prisoner is 

 drawn back to the mandibles and devoured. If inadvertently 

 introduced into an aquarium containing tiny fishes, these insects 

 do an immense amount of damage in a short time. Fig, 1 illus- 

 trates the pupa of one of our commonest dragon-flies (Aeshna 

 hrevistyla) ; fig. la shows the underside of the head, with the 

 formidable lower labrum extended and the pincers open. 



