Biologists always need a way to put animals and plants into groups. This helps to find their differences and similarities, and helps to make predictions about how new organisms may behave. This can be a pretty hard task when some creatures look very similar, are very small and have different life stages. For some creatures you need microscopes and dissecting equipment to work out which is which.
Classifying living things has been a real team effort. All of the scientists who have studied living things use the information that other experts have left for them. Often the information is in the form of keys. Keys can be quite easy to use for very different creatures, but they can be very complicated for similar species. It is usually necessary to be able to see your sample, and even better if you can use a magnifying glass or microscope.
One of the most common sorts of key is called a dichotomous key. It always gives you two choices for each step of the way.
Example 1: Dichotomous Key
What type of winged insect is it? This key will direct you to some of the common insect orders.
Remember that to start this key you need to have an adult insect. It should have 6 legs, 2 antennae, 3 body parts and wings.
1b has only got 2 wings and 2 tiny “drumsticks” (halteres) where the wings join………………… Diptera )
two white halteres on a fly• four wings…………………………………………………………………………………………………………………………………….3.
3. • the outer wings form a hard cover that hugs the full length (but not past the end) of the abdomen. You usually can’t see the pair of wings underneath because the outer wings are not see through. …………… 4
hard beetle outer wings (elytra )
colourful bug wings
• the outer wings are held like a tent over the abdomen or don’t reach the end of the abdomen………………… 5
wings of a Butterfly stretching away from the body. 4. • the central meeting point of the insects wings joins in a straight line all the way down the centre of the abdomen…………..beetle ( Hemiptera )
beetle: outer wings meet in a straight line down the centre of the abdomen. 
true bug: wings do not meet in a straight line
5. • the wings are covered in scales …………………………………………………………………………………………………………………………… butterfly or moth ( Orthoptera )
grasshoppers have strong back legs. 
cockroach legs are all of similar strength
• most legs look like they have a similar strength……………………………………………………………………………………………………………………….. 7
7. • body has a narrow neck and waist. ………………………………………………………………………………………………………………………………………… wasp or ant ( <href=”https://tasmanianinsectfieldguide.com/genus-cotesia”>Hymenoptera )
narrow neck and waist • body is oval shaped with spiky legs ……………………………………………………………………………………………………………………………………….. cockroach ( <href=”https://tasmanianinsectfieldguide.com/blattodea-cockroaches”>Blattodea )
no waist and an oval body