Snail Observation Exercise

Author: Matt Wedel

Overview: In this exercise, each student is given a pond snail in a clear glass and asked to make observations on the snail’s form and behavior. One of the key ideas is that seemingly common subjects (like snails) often have surprising or interesting properties, if only we take the time to look carefully.

Lesson Concepts:

• Observation is a key step in science.

• Field sketches aren’t art. They are meant to communicate information about something that you observed, so that someone else can identify (and perhaps find) it.

• Plants and animals vary in their physical traits (such as morphology, color, pattern).

California Science Education Standards:

• 7d. Construct scale models, maps, and appropriately labeled diagrams to communicate scientific knowledge.

Grade span: 6-8 or 9-12

Materials:

• Freshwater snails. You can get large numbers of small pond snails from large pet stores such as PetsMart, usually for free. The snails are aquarium pests, and the stores are usually happy to get rid of them.

• Clear plastic cups. The size is not important, but smaller is better—you have to get the snails out of the cups at the end of the exercise, and tall cups make this difficult.

• Dechlorinated water, rainwater, or “aged” water from an aquarium. The snails should not be put into chlorinated water. If you let tap water stand for 24 hours, almost all of the chlorine will have evaporated. You’ll need enough water to fill all of the cups to a minimal depth of 1 or 2 cm.

• Hand lenses.

• A blank sheet of paper for every student.

Advanced preparation: None.

Time: 30 minutes.

Grouping: The students are encouraged to work on their own (provided you have enough snails).

Teacher background:

This is a very basic exercise on observation. No hypothesis forming or testing is incorporated into the exercise as written, but the exercise could easily be extended to include an experiment. Possibilities include timing the snails’ movements, investigating their food preferences, or even seeing if they can run simple (T-shaped) mazes.

Teaching tips:

The goal of the exercise is for the students to practice making careful observations. To that end, the teaching should be as hands-off as possible, and the students should have as much time as possible to make their observations.

Procedure:

Give each student a glass with a little water and a snail, a blank piece of paper, and a hand lens. Have them fold their papers in thirds, as when folding a letter, and then turn the pages sideways so that the folds form three columns. In the left-hand column, ask the students to write down their observations on the snails’ form—size, shape, color, texture, and so on. In the middle column, ask them to write down their observations on the snails’ behavior—does it move? If so, how? Does it travel in a straight line? A curving, twisted path? A circle? Where does the snail go in the glass—does it stay on the bottom, or climb the sides, or even swim upside down across the surface of the water? Ask the students to pick up their glasses and observe the snails’ broad, muscular foot. They may be able to see the mouth opening and closing near the front of the foot. Finally, ask the students to draw their snails in the right hand column of their papers. Remind them that sketches complement written observations, and don't have to be artistic to convey useful information (such as whether their snails are spotted or striped).

You may ask the students to place a drop of water on the palm of one hand and then set their snails on their hands. Don’t be surprised if some students are too squeamish.

Finally, if time allows, ask the students to trade snails with a neighbor, and then make lists of the similarities and the differences between the two snails.

Cleanup:

After the exercise is over, you’ll have some snails to deal with. If you got your snails from a pet store, don’t release them into the wild. They can serve as vectors for foreign disease organisms and contaminate native fish populations. I feed leftover snails to my turtle. If you don’t know any turtle enthusiasts, you might try freezing the snails before disposing of them.