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.
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.
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.