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Creepy Critters

What if a new planet was discovered that had life on it? Would you be able to figure out what known creatures these alien life forms might be related to? What would you look for to compare? How would you organize these different living things?

Scientists who study living things organize them into categories based on their relationships. Early classification systems were based simply on how things look. Now scientists focus on genetics, cellular make-up and other more specific things when they classify creatures.

Classification systems include big groups that are subdivided into smaller groups. Here's one way classification might work using cars as an example:


Imagine it's the year 2525. A planet similar to Earth has recently been found in a newly identified solar system in another galaxy. We have sent a space probe with a molecular transport beam to this planet to beam back a variety of different living creatures. Scientists examine the structure of each of these creatures and realize that they need to create a classification scheme to help them compare the alien life forms to each other and discover how they might be related.

The lead scientist sends you illustrations of the organisms and asks you to help develop this classification system. Your role is to study the illustrations and come up with a possible classification scheme based on the information provided about each organism. You'll be asked to explain to the scientific team how and why you organized the creatures this way. Print out these pages and follow the directions to do this activity at home. When you're done, come back to this page to test your newfound knowledge by answering the questions below. (No fair peeking at the answers before you do the activity!)

Note: This activity will take 30 minutes to 1 hour.

You’ll Need:

Note: Be careful handling sharp scissors.

What To Do:

1. Click on the link above for critter cards pages. Print out each page and cut out the cards. Keep the last four cards separate from the others.

2. Study all the cards except the last four, noting similarities and differences among the creatures. Create a table on your paper to help organize what you see. You might have columns to describe bristles, antennae, eyes, etc. You might want to number your cards to help keep track of which you're describing.

3. Now put the cards (except the four you've kept separate) into groups based on the similarities and/or differences you see. Each group should include creatures that have something in common. Now create a new table, listing the traits common to each group you've made.

4. Choose one of the cards from the four you've kept separate. This is a picture of a creature was just beamed back by the space probe and sent to you by the lead scientist. You need to decide where it fits in the group system you've just created. Do you need to make a new group for this creature or can you find some way to fit it into one of your existing groups?

5. Write a brief paragraph explaining your classification scheme, how it works and how easy or hard it is to fit new creatures into it.


  1. Why do we classify things?  Answer
  2. Is your way the only way possible to organize the critter cards?  Answer
  3. Do you happen to know the biological classification scheme used by scientists who study living things?  Answer


This experiment is based on an activity developed by the National Association of Biology Teachers.