A Little Bit More
When we think of snails, most of us think about those living in a marine environment. Anyone who has spent any time at the ocean, quickly realizes that there are many different kinds of snails (sea shell owners) living there. But there are terrestrial ones too as our unit poster points out. Land snails require water, at least for part of the year, as well as access to a source of calcium for their shells. Snails concentrate calcium from their environment in making their shells and this may attract other animals, especially birds at egg-laying time, searching for calcium for their own needs.
Land snails are members of a group (class) of animals called gastropods. There are over 50,000 living species of gastropods that include the marine snails and sea slugs, as well as freshwater and terrestrial snails. Although slugs are gastropods too, the fact that they have an internal, rather than external, shell means they’re not usually referred to as “snails” by the public. Although the marine snails greatly outnumber the other gastropods in number of species, there are still many different terrestrial snails all around the world.
Common land snail © John wiessinger
Most land snails are herbivores (eat only plants) and use a rod of tissue called a radula (RAD-u-la), studded with “teeth” to scrape off bits of food. Land snails can become a real nuisance in gardens and yards if their numbers become large enough. Land snails are preyed upon by birds, frogs, toads, snakes, and small mammals, even by some beetles. At times, a pile of empty snail shells can be found where a bird or mammal has habitually crushed them to gain access to the meat. These piles of shells can often provide researchers their best evidence of the presence of particular species for a given location.
Activities
Science – Snails Alive
Objectives: Observe snails as they feed and move about
Materials: Collected snails, 1 gallon jar, assortment of different plant leaves
Depending on where you live and the time of year, it may be easy for students to locate a few land snails and bring them in to class. Although you can order snails from a biological supply house, introductions of alien snail species has greatly reduced this option. In fact, maybe it’s best NOT to order any species that are not native to your area.
If you can locate a few animals, this alone will be a good exercise for some students. Finding snails isn’t quite as easy as it may seem but with a bit of persistence, it should be possible in many areas of North America. If one looks early in the morning, when there is a lot of dew or after a rainy day, the snails will be much more obvious as they crawl about the plants in search of food.
Once the snails are in the classroom, a simple 1 gallon jar can be set up for students to observe these animals. The jar needs a perforated lid, some plants inside for food and a place to crawl and just a bit of moisture. Too much moisture and you may get lots of mold growing there. If this becomes an issue, just remove the snails, clean out the inside of the jar and reconstruct.
With observation, the students should be able to see the snails feeding and will also be able to see the damage they can do to plants. Keep in mind that the snails will be more active in subdued light so don’t place in a sunny location if you want to see them in action. Introduce a variety of different kinds of plants (lettuce, dandelion leaves, tomato leaves, etc) to see if the snails have preference for one or more different foods. In fact, this might be a nice exercise to determine if the snails do have food preferences.
Questions
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