156 GOLDFISH VARIETIES AND 



INSECT ENEMIES OF FISHES 



Among the troubles that beset the fish culturists, not the least are 

 caused by insects and their larvae. This applies both to the propagators 

 of food fishes and those interested in fancy aquarium pets. We use the 

 term "insect" here in its popular sense and not according to exact scien- 

 tific definition. 



Some of these enemies are much more readily detected than others, 

 but most of them may enter the rearing tanks when so small that detection 

 is practically impossible. Wire screen or netting will keep out those that 

 fly, or a large enemy in the water can be separated from daphnia or other 

 living food by passing the "catch" through a fine wire gauze under water, 

 but despite these precautions it is essential in the summer season to be 

 ever on the lookout for any of the pests which may have gotten by our 

 keenest observation. Fortunately for the aquarist there are not many 

 kinds of insect enemies with which he is actively concerned. There are 

 only four, three of these being larvae. While the others are none the less 

 savage or fatal they are not so often met with, or else are so easily 

 detected that they are not such serious factors with which to reckon. 

 With the aid of illustrations made from specimens, mostly living, we will 

 proceed to give descriptions of the four arch-enemies in the order of their 

 destructiveness, and follow on with the others, adhering to the same plan 

 as far as possible. 



Water Tiger. This is the larva of the Predaceous Diving Beetle 

 (Dyttscus), itself also a very powerful but easily detected enemy. The 

 Water Tiger is easily the most rapacious, savage and insatiable enemy of 



Fig. 99. Water Tiger (Life she) 



young fishes. It does not wait for its prey to pass nearby, but adopts 

 business-like methods of going after its unwar}- victims. The flat head 

 is furnished with a strong pair of hollow mandibles, through which it 

 sucks enough blood to kill its victim and then wantonly goes after another. 

 In this way a single individual may kill an entire hatching of fish over 

 night. This larva can usually be recognized by its spindle-shaped body. 



