WATEK-BEETLES. 206 



snails to remove any confervse, for instead of eating tlie algae 

 the nnfortunate molluscs would be eaten by the beetles. A 

 single D. mwrginalis will live longer in confinement than a 

 pair would. One solitary beetle will sometimes survive two 

 or three years passed in captivity ; but when a male and a 

 female are kept together it will be generally found that after 

 a few months, perhaps owing to some conjugal misunder- 

 standing, the male dies. Celibacy certainly in this case 

 conduces to longevity. The males, when both sexes are 

 together, nearly always die first. The female, I believe, is 

 more rapacious than her mate ; she often eats him : he would 

 eat her, no doubt, if he had the opportunity. 



It is not a difficult matter to provide these beetles with 

 food, for they will eat small fish, young newts, little frogs, 

 tadpoles, water-snaUs, garden and other worms, insects and 

 larvas of insects, and pieces of raw meat. 



Dytisci are very destructive to the fry of fish, and often 

 kill more than they can eat. In the aquarium they will feast, 

 if no other food be given them, upon a small fish until 

 nothing but the skeleton is left. A good way to feed these 

 beetles is to put their food in a separate vessel (a large jam- 

 bottle will do), and remove them to it : when they have eaten 

 to repletion, return them to the aquarium, and throw the 

 discarded food and the water which the bottle contains away. 

 The beetles need only be fed thus twice a week, and their 

 aquarium will be kept quite clear and sweet; but if they are 

 not provided with a special vessel in which to feed, they 

 must be fed very carefully in their own tank, which should 

 contain a good supply of healthy growing weeds. The best 

 way to do this is to attach a piece of raw meat to a small 

 hook and suspend it in the water, removing it as soon as the 

 beetles have done with it. 



Though B. marginalis is such a terror to small aquatic 

 insects, they are avenged, for the " ogre " himself sometimes 

 dies under the ravages of a parasite. A water-mite (generally 

 Hydrachna globulus) at a certain stage of its existence is 

 frequently foiand living as a parasite upon this beetle, and 

 not seldom is the cause of its death. These parasites attach 



