The South Australian Naturalist. 



was coaxed into position with the aid of a thin stick. Its strong 

 mandibles immediately grasped the wood, and repeated shak- 

 ings failed to loosen the tenacious grip, even when the larva 

 was lifted out of the water; 15 minutes elapsed before its jaws 

 relaxed ! 



The Whirligigs {Gyrinidae) will be found in "schools," in 

 which formation they individually describe erratic circles on 

 the surface ; they are predaceous creatures, diving rapidly after 

 their animal food. The eyes consist of a double series ; the 

 upper ones apprise the Whirligig of the approach of an enemy 

 from above, and the lower set detects its prey in the water 

 beneath. 



Mention has been made of the "surface film." This film 

 is formed by the tension of the water at its point of contact 

 with the air : it is elastic and is capable of bearing some little 

 weight. Most of us are familiar with the trick of making a 

 needle "float''; in reality the needle does not float but merely 

 rests on the surface film. Deflect the point so that the film is 

 pierced and the needle sinks — literally falling through a tear 

 in the resisting surface. This little experiment is of interest, 

 for many of the specialized breathing organs of aquatic insects 

 depend for their efficiency on the resistance afforded by this 

 film. 



Water-bugs may be readily distinguished from their terres- 

 trial congeners in that the antennae are always small and more 

 or less concealed. Bugs undergo but an incomplete metamor- 

 phosis, and the individual is active and feeding during the whole 

 period of its life history. We are sure to find specimens of the 

 "fish-killers" lurking in the weeds. Reference to the two 

 illustrated species will show that both are marvels of protective 

 resemblance in accordance with their sluggish habit. The 

 Water-scorpion (Nepa tristis, fig. 2, Plate 2), with its flattened, 

 black body, has the appearance of a decaying, water-logged leaf, 

 whilst the cylindrical Ranatra (fig. 3, Plate 2), with its atten- 

 uated limbs, resembles nothing so much as a dead twig. The 

 name of Water-scorpion w^as applied to the Nepa on account of 

 a fancied resemblance to its namesake. The supposed "sting" 

 is in reality a long breathing tube and in a characteristic posi- 

 tion the insect will be found clinging to the weed with the tip 

 of this tube protruded just above the surface of the water; the 

 spiracles are situated at the base of this organ, which is also 

 possibly used as an ovipositor. The tube consists of two grooved 

 filaments, and in each of these the groove is lined with fine hairs. 

 Thus when they are adpressed to form a pipe the hairs interlace 



