Family HYDROPHILIDAE

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Introduction

The Hydrophilidae are a large cosmopolitan group of mostly aquatic beetles comprising 168 genera and 2803 species worldwide (Hansen 1999). The Australian fauna presently contains 43 genera and 206 species representing 26% and only 7% of the world's genera and species, respectively.

Hydrophilids can be divided into two major ecological groups, one aquatic, its species found mostly in still water situations and the other terrestrial or semi-aquatic, almost exclusively belonging to the subfamily Sphaeridiinae, and living in high humidity environments such as decaying organic matter, animal dung or in riparian situations.

Aquatic hydrophilids are poor swimmers using their legs alternately to swim rather than like oars as do dytiscids. They mostly inhabit shallow, still waters such as ponds, dams, bore drains, stock water troughs or slow moving water courses. However, those species with a stronger swimming ability, such as species of Laccobius Erichson, Berosus Leach or Sternolophus Solier, also occur in swiftly running water (Hansen 1987; Watts 2002).

Hydrophilids have a unique mode of respiration. Adults maintain a ventral air bubble by use of a dense hydrofuge pubescence on the ventral surface that extends from the antennal club to the apex of the abdomen and acts as a plastron. Air exchange at the air-water interface is facilitated by the antennae which are used to break through the interface to reach the air. Air exchange is accomplished with the adult hanging abdomen down at an angle from the water surface and pumping fresh air into its tracheae. Hydrophilid larvae are metapneustic, relying on a stigmatic respiratory chamber (atrium) formed from the eigth abdominal segment with various lobes and setae of varying lengths attached, whereas Berosus larvae are truly aquatic, being apneustic with pleural gills for breathing (Anderson 1976; Hansen 1987; Lawrence & Britton 1994; Spangler 1991).

Adults are scavengers, feeding on plants or decaying plant matter, and larvae are predaceous, feeding on a variety of snails, worms, small crustaceans and insect larvae. An exception is Helochares Mulsant which is phytophagous (Anderson 1976; Hansen 1987).

Hydrophilids enclose their eggs within a densely woven silk cocoon with one end drawn out into an elongate mast that helps with respiration. Most cocoons are attached to emergent vegetation just above water level or in riparian situations adjacent to water. However, Spercheus Kugelann and Helochares adults carry the eggs ventrally in a bag on the surface of the abdomen, while the cocoons of Hydrophilus Geoffroy and Hydrochara Berthold float freely on the water (Lawrence & Britton 1994; Hansen 1987). The terrestrial sphaeridiines leave their egg cocoons amongst decaying organic matter (Hansen 1990).

General descriptions and illustrations of the immature stages can be found in Bertrand (1972, 1977) and Spangler (1991). Watts (2002) gives an illustrated larval key to 21 aquatic hydrophilid genera in Australia. The larval forms ofAgraphydrus Régimbart, Notohydrus Balfour-Browne, Paranacaena Blackburn and Phelea Hansen are not yet described.

The aquatic hydrophilids are reasonably well known due to the work of Gentili (1981, 1989, 1991, 1992, 1993, 1996a,b, 2000) mostly on Laccobius Erichson and Anacaenini, while Watts has revised most of the remaining genera: Berosus (1987, 1997), Hydrophilus (1988), Sternolophus (1989), Hydrobiomorpha Blackburn (1990), Agraphydrus, Chasmogenus Sharp, Helochares (1995), Amphiops Erichson, Alloctocerus Kraatz, Regimbartia Zaitzev (1998a), Enochrus Thomson (1998b), Hydrochus Leach (1999), Chaetarthria Stephens (2000). Hebauer (1997) revised Spercheus on a worldwide basis and added a new species from north-west Australia (1999). The Australian genera of the subfamily Sphaeridiinae have been revised by Hansen (1990), but a number of genera still need revisionary work for a full understanding of their species diversity. Georissus Latreille, Limnoxenus Motschulsky, Coelostoma Brullé and Cercyon Leach have never been revised in an Australian context.

The last world catalogue was that of Hansen (1999). The classification used in this ABIF site follows that of Hansen (1991, 1999) except the basal lineages Spercheidae, Hydrochidae and Georissidae are here considered as subfamilies within the Hydrophilidae following Lawrence & Britton (1994). Five subfamilies are recognised in the Australian hydrophilid fauna: Georissinae, Hydrochinae, Hydrophilidae, Spercheinae and Sphaeridiinae. Subfamily Epimetopinae, the New Zealand Horelophinae and the mainly Holarctic Helophorinae do not occur in Australia. A summary of the classification follows:

Subfamily Georissinae
Georissus Latreille, 1809

Subfamily Hydrochinae
Hydrochus Leach, 1817

Subfamily Hydrophilinae
Tribe Anacaenini
Crenitis Bedel, 1881, Notohydrus Balfour-Browne, 1939, Paracymus C.G. Thomson, 1867, Paranacaena Blackburn, 1888, Phelea Hansen, 1999

Tribe Berosini
Allocotocerus Kraatz, 1883, Berosus Leach, 1817, Regimbartia Zaitzev, 1908

Tribe Chaetarthriini
Amphiops Erichson, 1843, Chaetarthria Stephens, 1835

Tribe Hydrophilini
Subtribe Acidocerina
Agraphydrus Régimbart, 1903, Chasmogenus Sharp, 1882, Enochrus C.G. Thomson, 1859, Helochares Mulsant, 1844
Subtribe Hydrobiina
Hybogralius Orchymont, 1942, Limnoxenus Motschulsky, 1853
Subtribe Hydrophilina
Hydrobiomorpha Blackburn, 1888, Hydrophilus Geoffroy, 1762, Sternolophus Solier, 1834

Tribe Laccobiini
Laccobius Erichson, 1837

Subfamily Spercheinae
Spercheus Kugelann, 1798

Subfamily Sphaeridiinae

Tribe Andotypini
Coelostomopsis Hansen, 1990

Tribe Borborophorini
Borborophorus Hansen, 1990, Petasopsis Hansen, 1990

Tribe Coelostomatini
Coelostoma Brullé, 1835, Dactylosternum Wollaston, 1854

Tribe Megasternini
Australocyon Hansen, 1990, Cenebriophilus Hansen, 1990, Cercyodes Broun, 1886, Cercyon Leach, 1817, Ceronocyton Hansen, 1990, Cetiocyon Hansen, 1990, Chledocyon Hansen, 1990, Ercycodes Hansen, 1990, Notocercyon Blackburn, 1898, Pilocnema Hansen, 1990, Pseudoosternum Hansen, 1990

Tribe Rygmodini
Eurygmus Hansen, 1990, Pseudohydrobius Blackburn, 1898, Rygmostralia Orchymont, 1933

Tribe Sphaeridiini
Sphaeridium Fabricius, 1775

 

General References

Anderson, J.M.E. 1976. Aquatic Hydrophilidae (Coleoptera). The biology of some Australian species with descriptions of immature stages reared in the laboratory. Journal of the Australian Entomological Society 15(2): 219-228

Bertrand, H. 1972. Larves et Nymphes des Coléoptères Aquatiques du Globe. Paris : Paillart 804 pp. [Date published 12/31/1972]

Bertrand, H. 1977. Larves et Nymphes des Coléoptères Aquatiques du Globe. Errata et Addenda. Abbeville : Paillart 19 pp. [Date published 12/31/1977]

Gentili, E. 1996a. Laccobius nuovi o poco noti di Sierra Leone, Pakistan, Vietnam, Australia, Sumatra, Filippine e Nuova Guinea (Coleoptera Hydrophilidae). Memorie della Società Entomologica Italiana. Genova 74: 21-32

Gentili, E. 1996b. Notes on the Anacaenini from Australia and Melanesia with descriptions of new species (Coleoptera, Hydrophilidae). Giornale Italiano di Entomologia 8: 177-189

Gentili, E. 1981. The genera Laccobius and Nothydrus (Coleoptera, Hydrophilidae) in Australia and New Zealand. Records of the South Australian Museum 18(7): 143-154

Gentili, E. 1989. Alcune novità sul genere Laccobius (Coleoptera, Hydrophilidae). Annali e Osservatorio di Fisica Terrestre e Museo Antonio Stoppani del Seminario Arcivescovile di Milano n.s. 10: 31-39

Gentili, E. 1991. Elementi per una revisione del genere Laccobius (Coleoptera, Hydrophilidae). Giornale Italiano di Entomologia 5: 381-389

Gentili, E. 1992. The Notohydrus of Australia (Coleoptera, Hydrophilidae). Bollettino della Società Entomologica Italiana 124(1): 21-26

Gentili, E. 1993. Paranacaena Blackburn, 1889: a valid genus (Coleoptera, Hydrophilidae). Giornale Italiano di Entomologia 6: 285-296

Gentili, E. 2000. The Paracymus of Australia (Coleoptera, Hydrophilidae). Records of the South Australian Museum 33(2): 101-122

Hansen, M. 1987. The Hydrophiloidea (Coleoptera) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica. Leiden : E.J. Brill Vol. 18 254 pp.

Hansen, M. 1990. Australian Sphaeridiinae (Coleoptera: Hydrophilidae): a taxonomic outline with descriptions of new genera and species. Invertebrate Taxonomy 4(2): 317-395

Hansen, M. 1991. The Hydrophiloid beetles. Kongelige Danske Videnskabernes. Selskabs Skrifter. Kjøbenhavn 40: 1-367

Hansen, M. 1999. Hydrophiloidea (s.str.) (Coleoptera). pp. 1-416 in Hansen, M. (ed.). World Catalogue of Insects. Stenstrup : Apollo Books Vol. 2 416 pp.

Hebauer, F. 1997. Revision der Arten der Familie Spercheidae Erichson, 1837 (Coeloptera, Hydrophiloidea). Entomologische Blätter für Biologie und Systematik der Käfer 93(1): 9-42

Hebauer, F. 1999. Spercheus wattsi sp. n. — a second Australian species of the genus (Coleoptera, Hydrophiloidea). Acta Coleopterologica 15(2): 5-6

Lawrence, J.F. & Britton, E.B. 1994. Australian Beetles. Melbourne : Melbourne University Press x 192 pp.

Spangler, P.J. 1991. Hydrophilidae (Hydrophiloidea). pp. 355-358 in Stehr, F.W. (ed.). Immature Insects. Coleoptera and Diptera. Dubuque, Iowa : Kendall-Hunt Vol. 2 xvi 975 pp.

Watts, C.H.S. 1998a. Revision of Australian Amphiops Erichson, Allocotocerus Kraatz and Regimbartia Zaitzev (Coleoptera: Hydrophilidae). Records of the South Australian Museum 30(2): 93-106

Watts, C.H.S. 1998b. Revision of Australian Enochrus Thomson (Coleoptera: Hydrophilidae). Records of the South Australian Museum 30(2): 137-156

Watts, C.H.S. 1987. Revision of Australian Berosus Leach (Coleoptera: Hydrophilidae). Records of the South Australian Museum 21(1): 1-28

Watts, C.H.S. 1988. Revision of Australasian Hydrophilus Müller, 1764 (Coleoptera: Hydrophilidae). Records of the South Australian Museum 22(2): 117-130

Watts, C.H.S. 1989. Revision of Australasian Sternolophus Solier (Coleoptera: Hydrophilidae). Records of the South Australian Museum 23(2): 89-95

Watts, C.H.S. 1990. Revision of Australian Hydrobiomorpha Blackburn (Coleoptera: Hydrophilidae). Records of the South Australian Museum 24(1): 35-42

Watts, C.H.S. 1995. Revision of the Australasian genera Agraphydrus Régimbart, Chasmogenus Sharp and Helochares Mulsant (Coleoptera: Hydrophilidae). Records of the South Australian Museum 28(1): 113-130

Watts, C.H.S. 1997. Three new Berosus Leach (Coleoptera: Hydrophilidae) from Australia. Records of the South Australian Museum 29(2): 147-152

Watts, C.H.S. 1999. Revision of the Australian Hydrochus (Coleoptera: Hydrochidae). Records of the South Australian Museum 32(1): 1-43

Watts, C.H.S. 2000. Revision of Australian Chaetarthria Stephens (Coleoptera: Hydrophilidae). Records of the South Australian Museum 33(1): 29-31

Watts, C.H.S. 2002. Checklists & guides to the identification, to genus, of adult & larval Australian water beetles of the families Dytiscidae, Noteridae, Hygrobiidae, Haliplidae, Gyrinidae, Hydraenidae and the superfamily Hydrophiloidea (Insecta: Coleoptera). Identification & Ecology Guide No. 43. Albury : Co-operative research Centre for Freshwater Ecology viii 110 pp.