Fig. 13:31. Hydrophil idae, adults, a, Berosus dolerosus; b, 

 Pemelus costatus; c, Epimeiopus thermarum; d, Hydrochus 

 variolatus (a,c,d. Leech, 1948; b, Horn, 1890). 



with the unwettable hairy club of an antenna. This 

 provides a funnellike point of contact with the exten- 

 sive bubble held on the undersurface by the hydrofuge 

 hair, the bubble in turn being connected with the 

 subelytral storage chamber. A pumping action of the 

 abdominal segments forces out the old supply and 

 brings in fresh air. 



As has been shown by Hrbacek (1950), the manner 

 in which contact is made with the air varies among 

 different genera. In all but Hydrochus the antenna is 

 raised (fig. 13:33a), with the unwettable part of the 

 club in contact with the film of air on the hydrofuge 

 pubescence behind the eye. As the top of the bent 

 antenna reaches the surface (fig. 13:336), the surface 

 film breaks to form a funnel (fig. 13:33c), and the 

 antenna is moved to another position. In Hydrochus 

 the antenna is held in front of the eye as the beetle 

 surfaces (fig. 13:34c). 



The species of all genera Hrbacek studied, except 

 Helophorus, normally turn a little sideways as they 

 reach the surface, and break the film with one antenna. 



335 

 Leech and Chandler: Coleoptera 



The species of Helophorus rise so that the whole back 

 of the head is near the surface, then push up both 

 antennae to form a broad funnel across the back of 

 the head (fig. 13:34a). 



The length of the funnel is important, for ai and 

 above a critical distance of about 1.5 mm., only an 

 air canal, comprising the unwettable antenna! seg- 

 ments themselves, is formed. But at Less than 1.5 mm. 

 the surface tension is stronger than the hydrostatic 

 pressure, and a real funnel is possible. The length of 

 the unwettable part of the antennal club is also signi- 

 ficant. Beetles with long and specially formed club 

 segments, such as Hydrophilus (the Hydrous of 

 Hfbacek's paper) are able to reach fresh air while the 

 body is relatively deeply submerged (fig. 13:34 6). Some 

 strong swimmers, such as species of Berosus, are 

 able to rise forcefully enough to obtain air even when 

 their antennae have been removed. They break the 

 surface film with the unwettable sides of the head, 

 especially the gonao, to form a funnel. 



The coprophagous Sphaeridiinae, which live in 

 damp or wet places but are rarely aquatic, can break 

 the surface film with the antennae, but not so effi- 

 ciently as do the truly aquatic forms. In fact, 

 Hrbacek found that such coprophagous Scarabaeidae 

 as Aphodius and Onthophagus readily used their 

 antennae to make air funnels, though the air film on 

 the body could not last more than twelve to twenty- 

 four hours because of the shape of the body and lack 

 of hydrofuge pubescence. 



Hydrophilid larvae (except those of Helophorus and 

 Berosus) are metapneustic, that is, only the posterior 

 pair of spiracles is open and functional; the tracheae 

 leading to these spiracles may be enlarged to form 

 air reservoirs. Larvae of Helophorus spp. have nine 





^ 



Fig. 13:32. Hydrophilidae. a, Cercyon sp,, ventral surface of 

 adult; b, Hydrochara sp., clypeus and labrum of adult; c, Neo- 

 hydrophilus sp,, clypeus and labrum of adult; d, Helobata sp., 

 head and prothorax of adult; e, Megasfernum sp., front tibia of 

 adult; f, Cercyon sp., antenna of adult (o, Mulsant, 1844; b,c, 

 D'Orchymont, 1912; d-f, Horn, 1890). 



