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.
Coleoptera (beetles) is the most speciose of all the insect orders.
The majority of the approximately 120 families known from Australia are
terrestrial but around 14 are wholly aquatic or strongly associated with water
and a further 5 include some aquatic or semi-aquatic species.
This key identifies these 19 families but may not distinguish members of
this 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.
The chief distinguishing feature of adult beetles is that the front wings
form hardened elytra. The elytra
cover and protect the membranous flying wings, which are rolled and folded
underneath the elytra at rest. The
elytra meet at the midline of the abdomen, never overlapping as do the hemelytra
of some hemipteran bugs. Functionally,
the body of an adult beetle is peculiarly divided not into head, thorax and
abdomen as in most other insects, but head, prothorax and hind-body.
The hind-body comprises the pterothorax and abdomen, fused broadly
together. Beetle mouthparts usually are of biting type.
The adult head sometimes has two ocelli but never three, an often none.
The abdominal sternum often displays a reduced number of visible
sclerotised plates (sternites). The
first few are reduced and concealed beneath the hind coxae, and the terminal
segments usually are telescoped into the apex of the abdomen.
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). Myxophaga is
a small suborder comprising minute, globose beetles. Adephaga includes a wide range of body sizes and two general
body shapes: one in which the head, prothorax and hindbody are well separated
from each other, the other in which they fit closely together to give a smooth
lateral outline and overall a boat-shaped appearance. Polyphaga includes all these shapes and more.
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.