Name_______________________ Per. __________
Making a Dichotomous Key
A dichotomous key is a device that can be used to easily identify an unknown organism. The word
dichotomous comes from two Greek words that together mean, "divided in two parts". A dichotomous key
consists of a series of two part statements that describe characteristic of organisms. At each step of a
dichotomous key the user is presented with two choices. As the user makes a choice about a particular
characteristic of an organism they are led to a new branch of the key. Eventually the user will be led to the
name of the organism that they are trying to identify.
Procedure
1. Study the numbered drawings of 18 beetles.
2. Choose ONE characteristic of the beetles and sort the beetles into two groups based on whether they have
the characteristic or not. Take measurements if you wish.
3. Record the chosen characteristic on the diagram and write the numbers of the beetles under either Group
1 or Group 2 on your diagram.
4. Select another characteristic of each subgroup, and repeat steps 3 for the next level down on your
diagram.
5. Repeat this process until you have only one beetle in each group.
6. Once your diagram is complete, use it to create a dichotomous key for the beetles. To do this, create a
series of numbered steps with the first step showing the first characteristic you used. At each step, offer
two choices for classifying the beetle based on a single characteristic. For example, you may have used
the characteristic “antennae longer than front legs” as your first dividing characteristic. Your first
numbered step in your key would be (1a) antennae longer than front legs or (1b) antennae not longer
than front legs.
Parts of a Beetle:
Specifically shown a Stag Beetle
*Helpful Tips*
 IT may be helpful to use this sheet and cut them out.
 Then form them into a working diagram.
 From that diagram – then make your written “flowchart” /Diagram
Then you will have your layout to use in writing out the DK
steps.
1a
1b
2a
2b
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
10a
10b
11a
11b
12a
12b
13a
13b
14a
14b
15a
15b
16a
16b
17a
17b
ANALYSIS:
1.
Name 5 of the characteristics that you looked at in order to find the names of the beetles.
2.
How is a dichotomous key useful to scientists?
3.
What was the main trait that was the difference between beetle 4 and 8?
4.
What was the main trait that was the difference between beetles 14 and 9?
5.
What was the main trait that was the difference between beetle 1 and 4?