52 TJie Soiitli Australian Naturalist. 



Now let us examine some of the insects commonly found 

 in the fresh-water pools and streams around Adelaide. The 

 collector should repair to weed-grown pools such as occur below 

 the River Torrens weir, for these will be found to contain an 

 abundance of life during the summer months. By sw^eeping 

 amongst the weeds with a hand net most of the forms to be 

 enumerated will be taken. 



In such a pond, beetles of various sizes will at intervals 

 swim quickly to the surface, remain there for a short time, and 

 as rapidly descend, propelling themselves through the water by 

 means of their compressed, oar-like hind legs, which are fringed 

 with fine hairs. Amongst them may be a giant of the clan, the 

 Silver Water-beetle iHijdrophilKs pic ens) ; there are many 

 species of this family in South Australia, but none is so large 

 as this introduced species. When captured it should be 

 cautiously handled, for beneath the breast is a strong spine, 

 which may be pushed through the skin as the insect struggles 

 to escape. The appearance of this beetle after it has obtained 

 a supply of air is resjjonsible for the common name. With the 

 aid of the antennae, air is carried down a groove in the thorax 

 and is entangled in hairs on the underside of the body, which 

 when so charged presents a silvery appearance underwater. 

 Two bristles at the termination of the abdomen are used by the 

 female in the deposition of the eggs, which, like those of other 

 species, are attached to water plants. The larvae do not in 

 any way resemble the adult, and, being carnivorous as well as 

 herbivorous feeders, are armed with a pair of strong mandibles. 

 Like the Squids of the sea, when disturbed they emit a black 

 fluid, which clouds the water and conceals their retreat. 



Members of the Dijtlscklae, unlike the Silver Water-beetle, 

 are carnivorous when adult, and will attack almost any other 

 inhabitant of the pond, including the last-named species. The 

 habits of the larvae were admirably described by Mr. Savage 

 in the last number of "The Naturalist" under the name of 

 "Water-tigers." Fig. 1, Plate 2, shows a larva and a male 

 and female of our commonest and largest species {Cyhister tri- 

 punctatiis) ; the perfect insect is over an inch in length and the 

 larva measures two inches. The male, the underside of which 

 is illustrated, is provided with a sucker on each of the front 

 legs, and may thus be readily distinguished. The colour of this 

 species is dark olive, with a yellowish stripe around the edges 

 of the head and wing cases. The larva is light yellow, with a 

 broad, dark brown stripe on the back; it is particularly fero- 

 cious in its habits. To obtain a photograph the example shown 



