48 NATURAL HISTORY OF AQUATIC INSECTS CH. 



Insects, Tadpoles, and Fishes are devoured by the 

 insatiable D}'tiscus larvae. Man}' a raw naturalist has 

 put them into his collecting-bottle or aquarium, to 

 find after a few hours that they have destroyed or 

 mutilated almost his whole live stock. 



The legs are long, and fringed with hairs, so that 

 they form efficient oars. When the larva swims about 

 in a leisurely way, the legs are the chief means of 

 propulsion. But it can also make a sudden spring, 

 by throwing its body into serpentine curves. It may 

 also be seen to creep on submerged leaves, and to 

 cling to them when resting or lying in ambush. The 

 legs end in double claws, which are probabh- useful in 

 seizing the prey as well as in supporting the bod}\ 

 Some other predatory Coleopterous larvze (Carabids 

 and Gyrinidae) have them too, but they are not 

 common in larvse of this order. 



The last segment but one is much narrowed, and 

 the last still more so. The tip of the tail carries two 

 small appendages. These, as well as the two last 

 segments of the abdomen, are fringed with hairs, 

 which no doubt increase the effect of a stroke given 

 to the water. But these appendages are chiefly used 

 to buoy up the tail, when the larva requires to 

 breathe. The larva is lighter than water, and can 

 only remain below by grasping solid objects. When 

 it lets go, it slowly ascends to the surface, and pushes 

 the tip of its tail into the air. The water rolls off the 

 hairy appendages in a moment, and then the larva is 

 suspended by its tail from the surface-film. The 

 success of the operation depends upon the circum- 

 stance that the particles of water hold more power- 



