Fig. 13:26. a, Staphylinoid wing; b, Hydrophiloid wing; c, 

 Ochthebius sp., mandible of larva (o,b, Crowson, 1950; c, Rich- 

 mond, 1920). 



and some have metallic colors; almost all have a 

 thin transparent border (fig. 13:25c?) around the prono- 

 tum, which is narrower at base than the elytra. The 

 species of Hydraena have greatly elongated maxillary 

 palpi (fig. 13:25e) and closely, rather coarsely punct- 

 ate elytra. Species of Limnebius have short palpi, are 

 black or dark brown, smooth, with very finely punctate 

 elytra, and a pronotum as broad at base as the elytra. 



Relationships. — In earlier studies the genera Hy- 

 draena and Ochthebius were often associated with 

 Hydrochus and Helophorus in a family Helophoridae, 

 and Limnebius placed in the Hydrophilidae. Later 

 they were placed as the tribes Hydraeninae and 

 Limnebiinae in the Hydrophilidae. In 1931 Boving and 

 Craighead kept them together in a family Limnebiidae, 

 but removed the family from the Hydrophiloidea to 

 the Staphylinoidea, basing their opinion on larval 

 characters and the wing venation of the adults. 



The hydraenids are like most hydrophilids (fig. 

 13:25a) in having a transverse (clypeo frontal) suture 

 on the head, but entirely lack the posterior median 

 suture which gives it a Y-shaped form in the Hydro- 

 philidae. They differ also in having six or seven 

 rather than five visible abdominal sternites; the 

 antennae have five pubescent segments beyond the 

 cupule (fig. 13:25c) instead of only three (fig. 13:256); 

 there is no distinct bisetose empodium between the 

 tarsal claws. 



They resemble the Staphylinoidea in wing venation 

 (the m-cu loop is greatly reduced or absent, compare 

 figs. 13:26a and b), but Crowson (1950) has suggested 

 that this may be an incidental effect of small body 

 size and not of phylogenetic value. They resemble 

 the Staphylinoidea also in having a ninth abdominal 

 sternite and no basal piece to the aedeagus and dorsal 

 ocelli in a few species, but are like hydrophiloids 

 in the form of the metendosternite, absence of femoral 

 plates on the hind coxae, elytra fully covering the 

 abdomen, and aquatic habits. 



Respiration. —The ventral surface of an adult, ex- 

 cept the head, legs, and abdominal tip, is covered 

 with short dense hydrofuge pubescence. This unwet- 

 table pile holds a pillowlike bubble of air over the 

 lower surface of the beetle while it is under water. 

 To replenish this and the subelytral supply, a beetle 

 crawls to the surface and assumes a nearly horizontal 



331 



Leech and Chandler: Coleoptera 



position. It thon inclines ita bod) to one side, to 



bring tho angle between the head and prothorax to the 

 surface, and breaks through the surface film with n- 



hydrofuge antenna! club. Tins opens a funnel-shaped 

 passage to the ventral air bubble, and by pulsating 

 its abdominal segments the beetle is aide to change 

 the old air for fresh in a short time. Except at this 

 time the antennae are tucked away beside the eyes, 

 and the tactile role they play in terrestrial beetles 

 is taken over by the elongate maxillary palpi. 



Hydraenid larvae are holopneustic, that is, all 

 nine pairs of abdominal spiracles are open and func- 

 tional; hydrophilid larvae (except those of Helophorus) 

 are metapneustic, having only the terminal ones open. 



Life history. — The eggs are laid in the spring 

 singly, on stones or algae in shallow water, or out of 

 the water but in damp places. Those of Limnebius 

 and Ochthebius are either naked, or more or less 

 covered with loosely applied silk (fig. 13:276); those 

 of Hydraena are protected by a blanketlike covering 

 of closely applied silk (fig. 13:27a). They hatch in 

 seven to ten days. 



The larvae (fig. 13:28) are holopneustic, as men- 

 tioned above, and swim clumsily or not at all. They 

 walk and run quickly, and being predators, spend 

 their time hunting in the damp sand and silt at the 

 waters edge. They mature in about two months and 

 form pupal cells in damp situations. Some species 

 of Ochthebius make mud cocoons on the sides of 

 stones. Winter is passed in the adult stage. 



Habitat and distribution.— The larvae are adapted 

 as land crawlers and are found at the margins of 

 ponds, lakes, streams, and rivers, especially where 

 filamentous algae are present. Adults of some species 

 tunnel in the damp sand or soil at the waters edge, or 

 make use of tunnels excavated by Bledius (Staphy- 

 linidae) and Dyschirius (Carabidae) and similar littoral 

 forms. Adults of other species cling to stones well 

 out in running water. Species of Ochthebius are com- 

 monest in and around ponds, lakes, and saline waters; 

 those of Hydraena and Limnebius along streams and 

 rivers. 



Ochthebius bruesi Darlington was described from a 

 hot spring (temperature 38.8°C) south of Beowawe, 



Fig. 13:27. a, Hydraena pennsylvanica, egg; b, Ochthebius 

 fossafus, egg (Richmond, 1920). 



