'H6 The South Australian Naturalist. 



This was an iinAvelcome sight to- me, for I knew that my 

 fish were in clanger. Dytiscus tackle all insects and most other 

 small life in the pond, including fish. Only recently I had been 

 watching the destructive Avork of this larva on the tadpoles of 

 all sizes in the ponds at the back of Henley Beach ; fully-grown 

 tadpoles could be seen swimming about with gashes in their 

 bodies and their entrails dragging along behind, caused by the 

 fierce attacks of these larvae. 



I watched at my fish pond only a minute, when another 

 larva caught a fiy, and by putting a small net into the Avater I 

 caught no less than six larvae in one sweep. The dytiscus 

 larvae, although but three-quarters of an inch in length, have 

 very formidable mandibles, with which they attack their foes. 

 The mandibles are perforated at the ends, so that they can suck 

 through them, and once they get a grip there is no release until 

 all available nourishment is sucked from the victim. 



The water beetle is very interesting, although I much prefer 

 not to see him in my fish pond. The larva has a large head, 

 which is narrowed behind. Its body is clothed with such hard 

 integument that it may be said to be trul.y armoured, and it has 

 mostly its own way in the pond. I placed one in a glass 

 aquarium a few days ago with half-a-dozen water snails, and in 

 a short time he had fixed his mandible firmly into one of the 

 snails as it crawled up the glass. Of course, the snail imme- 

 diately drew itself inside its shell, but the suddenness of the 

 attack caused it to release its hold on the glass and it fell to the 

 bottom, the dytiscus still with its mandibles embedded. Next 

 day I looked at the aquaria, and not one of the six snails was 

 alive ; all of them had succumbed to the dytiscus larvae. I then 

 placed six larvae in a small aquarium together, and it was not 

 long before a pitched battle started. The vanquished in the end 

 proved to be the meal of the victors ; for three days they dis- 

 appeared one at a time till only two were left, and these appar- 

 ently lived happily together. 



The larvae breathes air through spiracles on the sides of the 

 abdominal segments, and they come to the surface tail upper- 

 most, and in that position appear to breathe through the pos- 

 terior spiracles in particular. When the larvae is fully grown 

 it crawls out of the water and buries itself in the soft damp 

 earth. There the metamorphosis takes place. As the warm 

 Aveather of spring or summer arrives it awakens from its sleep 

 and emerges from the pupae case a perfect insect. It is not long 

 away from the water, hoAvever. It craAvls to the top of adjacent 

 rushes or grasses and dries its wings, and flies back to the AA^ater. 



