54 The South Australian Naturalist. 



and prevent the ingress of water. The Nepa swims slowly and 

 awkwardly with the aid of the four hind legs, but unless dis- 

 turbed it remains motionless with the terrible pair of front legs 

 extended in readiness to grasp any small fish or insect which is 

 unfortunate enough to venture within reach. The fore legs are 

 strengthened and modified to hold living prey w^ith no possi- 

 bility of its escape. The edge of the broad thigh has a deep 

 furrow into which the leg and tarsus fit like the blade of a 

 pocket-knife into its handle. The comparatively large head 

 bears a strong rostrum or beak, in reality a case containing an 

 assortment of piercing instruments. Whilst a victim is held 

 firmly in the pincers, this beak is plunged into its body and the 

 carcass is relincpiished only when its juices are extracted. The 

 Nepa can inflict a painful little wound by driving its beak into 

 the flesh. Although of such a dingy hue under water, this 

 species has a much more inviting appearance with the wings 

 spread; these are of a warm brown tint and the upper surface 

 of the abdomen is brilliant scarlet. The eggs are small and 

 have some thin filaments attached to one end. At least two 

 species of this genus occur in our rivers. 



The Ranatra has an insatiable appetite, and its habits are 

 much the same as those of the Nepa. The prehensile fore-legs, 

 somewhat similar to those of the Mantis, are each armed with a 

 spine Avhich precludes the chance of living prey struggling from 

 their grasp. The eyes are large, each of them being as big as the 

 actual head. 



The Back-swimmers {Notonectklne) are perhaps the best 

 known members of this group. Their manner of progression is 

 unusual, for they swim through the water upside down, propelling 

 themselves with the aid of the long, hair-fringed hind-legs. Air 

 is obtained at the surface, and is stored in a reservoir between the 

 wings and the back of the body. I^nlike the other two bugs 

 mentioned, they are very active, but likewise possess strong beaks 

 and obtain their sustenance by sucking the juices from the bodies 

 of other aquatic creatures. These insects also cling to the stems 

 of aquatic plants and other submerged objects. (Fig. 4, Plate 2.) 



The Water-Boatmen {Corixidae) occur in greater numbers 

 than any of the other bugs found in the Torrens ; they breed dur- 

 ing the autumn months and, if conditions are favourable, multiply 

 to a prodigious extent. A very large globule of air is carried, 

 extending over the whole underside of the body ; Water-boatmen 

 are thus enabled to remain underwater for long periods without 

 coming to the surface. They have hair-fringed swimming legs 

 like the Notonectklae, but unlike the members of that family, they 

 swim in a more normal position — with the back uppermost. (Fig. 



