Acknowledgments

The following people must be thanked for their contributions to this key.  Ben Gunn (CSIRO Entomology), for his contribution of taxa and character images.  John Lawrence (CSIRO Entomology), Gunther Theischinger (NSW Environmental Protection Authority), and Tom Weir (CSIRO Entomology), for the loan of many of the specimens that were used for photography.

General Information

Coleoptera

The Coleoptera (beetles) is the most speciose of all the insect orders with over 5,000 aquatic species.  The majority of the approximately 120 families known from Australia are terrestrial but around 10 families are exclusively aquatic as larva and adult, an additional few are predominantly aquatic as larvae and terrestrial as adults or vice versa, and several more have sporadic aquatic representation.  This key identifies 19 families but may not distinguish members of the aquatic or semi-aquatic set from all other, terrestrial, beetles.

Coleoptera undergo holometabolous development, meaning there is an abrupt change of body form at the final moult.  It is convenient to deal with adults and larvae in separate keys.

Larvae are very variable, all with distinct sclerotised head, strongly developed mandibles, 2-3 segmented antenna; 3 pairs of jointed thoracic legs, lacking abdominal prolegs; open peripneustic (9 pairs of spiracles) tracheal system, but variably reduced spiracle number in most aquatic larvae, some with lateral and/or ventral abdominal gills, sometimes hidden beneath terminal sternite.  Pupation terrestrial (except some Psephenidae); pupa lacking functional mandibles.

Identification to family level can be partly achieved on gross features such as size and shape, but in many cases requires a careful examination of external morphology.  There is much variation of body form within many families and large-scale characters can readily be misleading.  On the other hand it is never necessary to examine internal characters in order to identify a specimen to family level.

The Australian aquatic and semi-aquatic beetles fall into three suborders: Myxophaga (1 family: Microsporidae), Adephaga (6 families: Carabidae through Gyrinidae in the key), and Polyphaga (12 families: Hydrophilidae through Brentidae in the key).

A few families are instantly recognisable on the basis of unique characters.  Most specimens, however, will fall readily into one of several not necessarily closely related families and then may require close examination for final placement.

Mecoptera

The Mecoptera is comprised of nine families of which five families are known to occur in Australia.  Of these five families, only the Nannochoristidae are aquatic.  Nannochoristidae occur in Tasmania and the highlands of south-eastern Australia.  The larvae can be found in accumulations of  silt  in shallow, slow-flowing streams.  The larvae are carnivorous, feeding on larval chironomids and other dipteran larvae.