Challenge students to guess the length of an earthworm, then try using a ruler or tape measure to determine the actual size. Ask, What problems do you encounter? After watching how earthworms move, why do you think it's difficult to measure their true length? What is it about their bodies that might cause them to seem to shrink and grow? How do you think this helps them move through soil? Draw bar graphs comparing an estimate of a worm's length with its true length, both when stretched out and when shortened. After the investigation, ask students if they have new ideas about how worms move. Have students share their graphs with the class.
Invite students to brainstorm and chart responses to these questions: What do you know about worms? What questions do you have? How might we discover the answers? Which questions do you think we can answer through observation and investigation? Next, become investigators. Imagine how your students might test the following questions: Can worms recognize color? Can worms be trained to come to the top for fresh food? How do you tell the head from the tail? What foods do worms prefer?
Ask students to consider what they know about an earthworm's environment. What do you think worms do underground? What have you observed that makes you say this? How do you think earthworms might affect soil or other materials in the soil? How might we find out?
Put a 1-inch layer of moist soil into a jar or plastic 2-liter soda bottom. Sprinkle a teaspoon of uncooked oatmeal over it, then place a one-inch layer of moist sand on top. Or alternate layers of soil or potting mix and organic matter. Continue building layers until there are 2 inches of space at the top; make sure the top layer is soil. Place 12 to 20 worms in the container then cover it with a lid punched with airholes. Cover your container with dark paper or cloth to keep out light and place it out of direct sunlight. Keep the content of the container slightly moist. Invite students to predict what might happen in the container. After a week, remove the paper. Encourage students to record new ideas and questions that arise as they observe what has happened.
Invite your students to estimate how many worms live in 1 cubic foot of soil in your garden or schoolyard. Consider digging 1 cubic foot of soil from different areas, such as a wooded area or garden, and comparing populations. Students might compare temperature, composition, and location of their soil samples. Have them draw inferences about what might account for differing worm population densities.
Fill a plastic bag with once-living materials (e.g., cut fruit, moist bread) and hang the bag on the bulletin board with a sign reading, "What do you think is happening in this bag?" Encourage students to observe the bag and explain their predictions.