Coleoptera 



209 



two distinct areas. The extremely active whirling dance of these 

 beetles in ponds and streams is well-known. Their larvs are 

 like those of the Dyticids, but the hind-body segments bear paired 

 tracheal gills, whereas the grubs of the Dyticids breathe atmos- 

 pheric air through the tail. 



Hydrophilidae. — The Hydrophillda are a family of beetles com- 

 prising both purely aquatic forms (^Hydrofhillna) (fig. 115) and 

 marsh-living insects (Sphairidiinds). They are characterised by the 

 great length of the palps of the first maxillae ; in the aquatic genera 

 these are longer than the feelers, a character which at once separates 

 the family from the Dyticids. The Hydrophilids are distributed 

 in all parts of the world. 



Staphylinidae. — The Supkylinid^ or Rove-beetles are an exceed- 

 ingly large family principally character- 

 ised by their truncate elytra which are so 

 short as to cover only a small part of the 

 hindbody : the hindwings, when present, 

 have a very simple neuration and can be 

 completely folded beneath the elytra. 

 The hind-body has ten segments, but 

 the last two are usually retracted, so that 

 eight only are evident ; the segments are 

 freely movable and always well chitinised, 

 even those covered by the elytra. The 

 feelers have as a rule eleven segments, 

 but sometimes ten or nine. There are 

 five tarsal segments. The Rove-beetles 

 are usually narrow and elongate in form 

 and very active in habit ; they feed mostly 

 on small insects, molluscs and worms, 

 but some devour carrion, and others eat 

 vegetable substances. The larvse are 

 active and campodeiform with well- 

 developed legs and short two-segmented 

 (rarely one-segmented) cercopods. About 

 7000 species of Rove-beetles have already been described, and the 

 family is world-wide in its range. 



Pselaphidae. — The Psdaphida are a family of very small beetles 

 resembling the Staphylinids in their shortened elytra, but readily 

 distinguished by their three-segmented feet, and their abbreviated 

 hind-body in which only five segments can be recognised. The 

 palps of the first maxillx are very long, and the thighs are usually 

 clubbed. The Pselaphidse live among waste matter ; they occur 

 in all parts of the world. 



Scydmaenidae. — The Scydm^nida are a family of tiny beetles, 

 which differ from the Pselaphidz in their long elytra, almost or 

 quite covering the hind-body, and their five-segmented feet. They 

 are usually ovate in form, shining black or brown in colour ; they 



O 



Fig. 115. — Water - Beetle 

 {Hydrophilus piceus, L.). 

 Natural size. 



