FRESH-WATER BIOLOGY 



climbing than swimming, and, consequently, they keep nearer to 

 shore and to the shelter of submerged trash. In an aquarium 



beetles of the size of Coptotomus 

 and Laccophilus may be seen feed- 

 ing in groups on the bodies of 

 dragonfly nymphs and tadpoles much 

 larger than themselves, which they 

 have overpowered. Their own exceed- 

 ingly hard chitinous armor doubtless 

 protects them from being eaten by 

 the majority of aquatic carnivorous 

 animals. 



Egg-laying appears to have been 

 observed hitherto only in Dytiscus, 

 which deposits its eggs singly in 

 punctures made in the green stems 

 of aquatic plants. 

 The larvae are voracious creatures, armed with long sickle- 

 shaped mandibles, like those of the larvae of the families just men- 

 tioned, each mandible with so deep a groove on the inner side that 

 it amounts to a perforation opening at the tip and the base. The 



FIG. 1375. A predaceous diving beetle, 

 Dytiscus. 



FIG. 1376. Side view of the head of the larva and pupa of the diving beetle, Hydroporus. 

 (Drawings by Mrs. Helen Williamson Lyman.) 



basal aperture lies just within the mouth- opening when the tips of 

 the mandible are brought together. Nearly all the larvae of this 

 group capture only living prey, but a few like Hydroporus (Fig. 

 1376) will eat pieces of animals that have been killed for them. 



