Natural selection and evolution are core ideas in biology and, in fact, all of science. Natural selection can briefly be described the process by which those individuals whose traits best fit their environment are most likely to survive, reproduce, and pass their genes on to the next generation. One of the critical “raw ingredients” of natural selection is variation in a population. All natural populations (groups of organisms of the same species) vary in their traits based on the interplay between genetics and environmental factors.
This activity uses the common garden snail (Helix aspersa) to measure variations in a population. These animals are garden pests found throughout North America and are readily captured from around most neighborhoods in California. I generally pay my neighbor’s kids 5¢ a snail and end up with upwards of 40 snails in less than an hour.
Snails are incredibly easy to keep in the classroom. They can survive in the classroom almost indefinitely with regular feeding and cleaning. Keep snails in a plastic shoebox or glass terrarium. Keep the terrarium covered securely while letting in air for them to breathe. Snails are strong and can easily push off a plastic lid, so secure the lid with rubber bands if necessary. Stock their habitat with several wet paper towels and vegetables from the grocery store (lettuce, carrots, apples, etc.). Twice a week, clean out their habitat by throwing away the old paper towels and food and giving them new wet paper towels and food. If you are keeping the snails longer than a week, place pieces of chalk in each container since they need calcium for shell growth and repair.
At the end of your project, snails may be released if they were collected locally. It is often interesting to “tag” the snails before you release them with a dot of nail polish on their shells. Thus, individuals may be tracked over time. If you choose not to release these pests back into your neighbors’ gardens, they may be frozen then thrown away. The adventurous can try cooking and eating them. That’s right! The garden snails found in North America are the same species that is used in escargot. In the going further section, there are resources for how to make escargot – although beware… this may be traumatic to some of your students.
None required although familiarity with observation, measurement, and histograms is helpful (see Human Traits Survey lesson).