Here is a link off the Scholastic web site that allows your students to design a caterpillar based on certain environmental variables. The students get four scenes and have to choose the color, spines, and defense mechanisms of the caterpillar based upon the environment and nearby predator. This is really nice because not only does it make the students think about why they will construct their caterpillar in a certain way, it also asks them to explain why they made the choices they did. At the end of the exercise it examines each scene and tells them what might have been the best choices in each scene. They have the opportunity to print their caterpillars at the end of the activity.
This is a nice little activity for elementary classes.