200 FBESH-WATEB AQUAEIA. 



the part of scavengers. The herbivorous beetles, e.g., Hydro- 

 philus piceus, are especially suitable for the tank, and are 

 also perhaps more interesting in it than any of the others, 

 particularly in regard to their egg-laying arrangements. The 

 eggs of aquatic beetles are oval or oblong, and are placed 

 usually either in cocoons or upon or in slits of aquatic plants. 

 The larvae of both the carnivorous and the herbivorous beetles 

 are far too predaceous to be trusted in the general tank. 

 They are, however, full of interest, and quite worthy of 

 separate aquaria easily prepared for the purpose. If it is 

 wished that the larvse should change to the perfect beetles 

 while in confinement, it will be necessary to make for them 

 an especially arranged tank, for most of them pass their 

 pupal state not in the water but in the damp earth at its side. 

 Some larvse are a long time before they become pupae, while 

 others are only a few weeks. 



The carnivorous beetles are much more likely to be a source 

 of danger to their defenceless comrades during summer 

 than during winter. The keeper should therefore guard 

 against jumping to the conclusion that since he has been able 

 to keep certain of the Bytiscidce among fish without the latter 

 sufEering any hurt during winter, he can always do so. 



The Hydradephaga are divided into two families : (1) The 

 Dytiscidce ; (2) The GyrinidcB. 



The Bytiscidce family numbers in Britain about 114 different 

 species ; but many of them are very locally distributed. 

 These beetles, which prefer stagnant to running water, are 

 extremely predaceous, and devour small fish, tadpoles, insects, 

 larvse of insects and beetles of their own and other species. 

 They have good powers of flight, and frequently travel, chiefly 

 during the evening, from one piece of water to another. No 

 pond or puddle seems to be too small for them. They have 

 often been found in the latter which had been formed by recent 

 rains. An instance indeed is recorded of a Dytiscus being 

 discovered in a tumbler of water after a shower. They have 

 also been known to dart at and kill themselves against the 

 roofs of greenhouses and the like, under the idea that they 

 were flying into water. They are said to be influenced by 



