How to identify bugs
aim of this tutorial is to address the most common issues we have
come across when teaching new staff in bioassessment.
|Notes before beginning
- This tutorial can be your entry into either major group level
identifications (i.e. sorting) or family level identifications.
- It is assumed that you will be using the online guide to the
Identification and Ecology of Australian Freshwater Invertebrates
(Hawking et al. 2006+) at www.mdfrc.org.au/bugguide
however, you can still work through the tutorial using other resources.
- Macroinvertebrates are usually preserved in 70% ethanol. Preservation
in 70% ethanol will cause some features to change so be careful
of live animal features listed in couplets that will not be observable
when dead. See
- Whenever you identify a taxon that you have not had previously,
it is good practice to make taxonomic notes i.e. key reference,
couplet number and list the features in that couplet that you
actually saw. This is not just copying the couplet word for word,
as not all features can be seen every time you identify an animal.
Also, add in the bits that were difficult or of particular note
so that when your identification is verified, and if it is incorrect,
you can track down where you went wrong and learn from the mistake.
Taxonomic verification does not always occur so close to identification
that you can remember exactly what you were thinking at the time.
- It is also beneficial to take images of each new taxon you
identify. These should at least be dorsal and ventral images of
the whole animal. If the equipment is available then also take
a few images of the most defining features. Ideally these images
are taken via a digital camera mounted on a microscope, however,
many general use digital cameras have a macro function or an optical
zoom function that can take reasonable images of macroinvertebrates.
- Your taxonomic notes, digital images and site information can
be combined into a voucher sheet for each taxon, creating a voucher
file for each project undertaken. The creation of a voucher file
enhances learning and is a good record for QA/QC purposes. See
list is not absolute but having this equipment will make identifications
- Stereo microscope: 10X magnification in eyepieces and capability
for 1 to 10X magnification in the objective lens - giving a total
magnification of 10 to 100X; both incident (above) and transmitted
(below) lighting with variable controls
- Squeeze bottle of 70% ethanol
- Several petri dishes of 60mm diameter in glass or plastic.
At the very least a translucent flat tray but not too large
- Fine forceps: at least 1 long pair (Dumont 55) and 1 extra
fine pair (INOX 5)
- Place the animal to be identified into a petri dish or other
small tray (not the channelled sorting tray as it is too difficult
to light the animal correctly).
- Cover animal with enough liquid (water or 70% ethanol) so that
the incident light does not cause glaring bright patches on the
animal (as this makes it difficult to see the key features) but
not so much liquid that the animal floats away every time you
- Good lighting is imperative, keep the incident light on full
unless the view becomes too shiny e.g. with adult beetles. The
transmitted light is useful for discrimination of setae and antennae.
Some dark beetles will also require side lighting to see the grooves
in hard dark surfaces of the elytra.
- For identification of major groups (sorting), the key generally
includes characters of the whole animal in dorsal or ventral view.
Do NOT pull anything off or out until absolutely necessary, the
less damage done to the animal the better.
- Dichotomous key couplets have a negative and positive answer
for each feature on each side of the couplet. Features are usually
listed in order of discrimination (or ease of visibility). See
- Read the first feature from each side of the couplet then look
at the animal. Do NOT try to digest the whole couplet before looking
at the animal as some couplets are long and wordy, especially
as you progress down the level of taxonomy. The first feature
may be so glaringly obvious that it negates the need to view all
the others, however it is always good practice to scan the animal
for the other features just in case you got the first one wrong.
ALWAYS look at the opposing couplet before viewing the animal
as sometimes it is easier to see what is not there.
- Be sure the animal is well focussed at all times and that the
particular part of the animal is in focus and being viewed from
the correct angle e.g. trichoptera antennae should be viewed from
above to estimate the length in relation to the front margin of
- You MUST interact with the microscope and animal. Zoom in and
out to find the best persepctive of the feature in relation to
the rest of the animal; constantly focus up and down to find the
best view of the feature; turn the animal around to get view from
differeent anles; alter the transmitted light to enhance some
features. What you need to do when, will come with practice.
- Become familiar with the taxonomic terms, it will make life
so much easier. In the beginning take the time to look up unknown
terms in the glossary
of the online bug guide. Do not spend the next few years calling
the frontoclypeus the "triangular thingy"!
images from the online bug guide will also help to
you know where on the animal to look for a particular feature.
Sometimes the descriptive image is a disembodied part.
- When using the online identification
keys; enlarge the descriptive images to see the key
features more clearly; key parts are lalbelled (noted in the text);
use images AND text TOGETHER; look where the arrows are pointing.
If the key feature is hard to see on the descriptive image then
it is going to be hard to view the key feature down the microscope.
That is the whole point of the digital images - everything looks
obvious on a 2-D line diagram.
- Use the distributions (listed as each taxonomic level is identified)
as a guide, but not an absolute. If your animal comes from Victoria
and you are struggling with the features listed in a couplet that
has one family only occuring in northern Queensland, then it is
most likely to be the other family.
- If your animal is small and you just can’t see the features,
consider that your animal is not at the usual life cycle stage
that allows identification. Taxonomic keys are created on the
features of final instar larvae or nymphs and mature adults. Immmature
animals or pupae may not have the same features and therefore
cannot be identified correctly. This will need to be confirmed
by someone with experience.
- If your animal just does not fit any key couplets, then consider
that you have a terrestrial animal. This will need to be confirmed
by someone with experience or by referring to some terrestrial
|List of Resources
J.H., Smith, L.M., Le Busque, K. (2006) Identification and Ecology
of Australian Freshwater Invertebrates. http://www.mdfrc.org.au/bugguide,
Version March 2007
| download PDF (117KB)