WATER-BEETLES 



25 



as their relatives in drier places. Such beetles are also very 

 numerous, and are readily observed when we quietly approach a 

 pool of stagnant or standing- water. We can detect their oval 

 and flattened bodies hanging head downwards, with the tip of 

 their abdomen at the surface of the water. When disturbed they 

 dive, and in doing so carry with them a bubble of air, which looks 

 like a liquid drop of silver, and which is utilized to sustain respi- 

 ration until the beetle feels safe again and rises to the surface. 

 Such beetles are well adapted for swimming, possessing a boat- 

 shaped body, usually quite polished, and having their long hind 

 legs broadly flattened and fringed with stiff hairs, so that they 

 can be used as oars. Such a leg is shown in Fig. lo, and it will 

 be noticed how admirably it is adapted for swimming. The 

 feelers of such beetles are long: and thread-like. The males of 



Fig 24. — Sucking disk of male Dj't/scus. Highly magnified. After Miall. 



some kinds possess a very remarkable sucking-disk (Fig. 24), 

 which is produced by dilating the first three pairs of the front tarsi ; 

 the females sometimes have the elytra furnished with deep fur- 

 rows. Both structures are of use during the mating season. All 

 the water-beetles, and still more so their dangerous looking 

 larvae, which possess powerful scissor-like jaws, kept in con- 

 stant motion, are savage and greedy, feeding upon tadpoles, 



