PREDACEOUS DIVING BEETLES. 



and the abdomen has six segments. Haliplid antennae 

 are lo-jointed and none of the legs are modified for swim- 

 ming. Dytiscid antennas are n -jointed and the hind 

 legs have fringes of long hairs, acting as oars. 



HALIPLID^: 



These beetles are small, oval, brown or yellow, more or 

 less spotted with black, and have very much rounded 

 backs. They are widest near the front of the elytra. 

 They crawl about aquatic plants, usually in shallow water, 

 but do not sw r im well. The larvae are slender and each of 

 the body-segments has a fleshy lobe on the back, the hind 

 one being long and tapering. Matheson states that they 

 feed on filamentous algas; if this be so, they are an excep- 

 tion to the carnivorous habits of the Adephaga. 



DYTISCID^; 



See above for the characteristics of these Predaceous 

 Diving Beetles. Their larvae (Plate LXXIV) are called 

 Water-tigers. The adults are said to hibernate in under- 

 water earth but they come out from time to time, especially 

 in early spring. During the summer they are frequently 

 attracted to lights. The males of certain genera, e. g. 

 Dytiscus, have the three basal segments of the front 

 (and, to a lesser extent, of the middle) tarsi modified to 

 form cup-like suckers, which may help them to cling to the 

 females while mating. Some females have furrowed 

 elytra. The adults have large spiracles near the hind end 

 and smaller ones along the side. When at rest, they 

 hang head-down with the tips of the elytra sticking out of 

 the water. In this way, the spiracles have access to the 

 upper air. When the beetle dives, a supply of air is 

 carried along under the elytra. Adults discharge, from 

 behind the head and also from anal glands, fluids which 

 differ somewhat from species to species but all of which 

 are probably defensive against fish and other enemies. 

 The mature beetles live for a long time, Harris having kept 

 a Dytiscus "three years and a half in perfect health, in a 

 glass vessel filled w r ith water, and supported by morsels 

 of raw meat." Eggs of Dytiscus, as far as known, are 



289 



