Creating a Dichotomous Key (Sorting beetles)

If you find an insect you have never seen before, how could you discover its identity? Many field guides help you match up the characteristics of your specimen with those of similar organisms using a dichotomous key. This identification key uses a series of paired comparisons to sort organisms into smaller and smaller groups. In this investigation, you will learn how to make your own keys to identification.

Look at the diagram at right. It shows the major, external structures of a typical beetle. Not all beetles have structures that look exactly the same. It is these differences in characteristics that make each species of beetle unique. Every species that has been identified has at least one characteristic that no other organism has.

During this lab you will be sorting 18 different beetles according to their similarities and differences and recording how you separated them into unique categories.

Materials  illustrations of 18 beetles  paper  sample dichotomous keys  ruler

Procedure 1. Look at the sample dichotomous keys to see how things (or organisms) can be grouped. 2. Study the illustrations of the 18 beetles shown on the cards. 3. Select one characteristic, and sort the beetles into two groups based on whether they have the characteristic or not. 4. Record the defining characteristic that identifies each group and list each beetle’s number under either Group 1 or Group 2 on your diagram. 5. Select another characteristic for each subgroup, and repeat steps 3 and 4 for the next level down on your diagram. 6. Continue to subdivide the groups until you have 18 groups with one beetle in each. 7. Using the characteristics shown on your diagram, construct a dichotomous key that someone could use to identify any beetle from the original cards. 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. Use the sample keys provided by your teacher to help you. Dichotomous Key Examples

A dichotomous key for the following list of specimens: pine tree, clam, rock, robin, tin can, deer, oak tree, mouse, dandelion, Paramecium, bicycle, ant

Potato Chip Key The population of potato chips used: -Lays Classic -Pringles Original -Lays BBQ -Lays Stax Sour Cream and Onion -Ruffles BBQ -Pringles Cheddar Cheese -Ruffles Original

1a. Plastic bag packaging 1b. Hard tube packaging

2a. Chips have ridged surface - go to 3 2a. Chips orange color= Pringles Cheddar Cheese 2b. Chips have non-ridged surface- go to 4 2b. Chips have other color-go to 3

3a. Chips orange color = Ruffles BBQ 3a. Chips solid tan with no speckles 3b. Chips tan color = Ruffles Original = Pringles Original 3b. Chips tan w/ greenish speckles 4a. Orange color = Lays BBQ = Lays Stax Sour Cream and Onion 4b. Tan color = Lays Classic Dichotomous Key Lab Sheet Name ______Pd. ______

Record your beetle groups and the characteristics that divide them, below. When you are done dividing up the beetles. Put together your final dichotomous key on the back of this sheet. Use either the diagram or written format in the examples

Did any other group produce a dichotomous key identical to yours? Explain why or why not.

Name some beetle characteristics that were not useful for creating your key? Explain why not.

Why does a key offer two choices at each step and not more than two?

Use print or electronic resources to find the scientific name for each beetle shown below.