Backyard and Seashore Science, Mollusks II: Snails and Slugs
Snails and slugs in the garden are labeled as pests. Snails cooked in garlic and butter is labeled a delicacy (for some)! To inspire curiosity and discover how your child feels about snails, start the conversation.
If your child finds a snail in a pond, clinging to a dock or the side of an aquarium, or if you purchase snails at a pet store for a science activity, studying snails will provide a great deal of fun and another terrific learning opportunity.
Snails are mollusks. Mollusks are animals with a soft body that is unsegmented or without distinct parts. Their bodies also tend to be long and moist. Mollusks are invertebrates, or without a backbone, thus the pliable bodies.
The phylum mollusk can be further broken down into different classes. For more information on one class called bivalves, or mussels, clams and oysters, see our post: http://guidingcuriosity.com/mollusks-kids-clams-mussels-oysters/
Snails and slugs are in the class labeled gastropods (Gastropoda, In Ancient Greek, gastro translates to stomach and pod means foot). This class also includes slugs and whelks. The large “foot” that their bodies sit on distinguishes gastropods. Snails also have heads and a one-piece shell (univalves). Clams and mussels are called bivalves because they have two shells and I would challenge anyone to find something on a clam or mussel that you would call its head.
Do all gastropods have shells? Snails do, but the answer to this question is no. “Slug” is the informal term we use for certain terrestrial gastropods with no external shell or a reduced internal shell that would not be visible. Limpets and abalone both have obvious external shells, but they cannot withdraw into them like most snails. Nudibranchs are a group of marine gastropods that are casually called “sea slugs” and include some of the most colorful and showy members of the entire animal kingdom. They shed their external shells after their larval stage. All these different animals are gastropods.
Snails and slugs are not the same animal. That is, slugs are not just snails that are somehow missing their shells. They are different animals! Snail shells are an integral part of the animal and they grow as the snail grows. A snail cannot simply crawl out of its’ shell. This is in contrast to hermit crabs which just “borrow” empty dead and discarded shells they come upon and have to change out to different larger ones as they grow.
(NOTE: Nudibranchs are distinctly different from several other groups of marine animals that are more formally called Sea Slugs.)
Investigations begin with a question, vocalized or not. If you see an inquisitive expression, you can help to guide an investigation by posing questions, or better yet, helping your child answer a question that she asked.
Where do snails live, or where do you go to find snails? Invite your child to go outside and see if she can find one in the garden, on a tree stump, under leaves, or in a stream, and describe the habitat. Perhaps she will only find empty shells, but this is a start to exploring these animals.
Try and let your child discover the answer to his question, but should you need to help, snails live in diverse habitats.
Depending on where you live, you should be able to find snails. Look for them in fresh water, salt water, brackish water, inter-tidal or 100% terrestrial habitats. Think of an odd place and chances are you will find a snail that lives there, such as a desert, ditches or deep in the ocean. They live near but not in the Arctic and Antarctica, so you cannot find them everywhere! Snails are nocturnal, but that means your child may have to devise a plan for finding them. Look in dark areas in a forest or the garden. Try early evening hours just as the light is dimming, or early morning when there is still plenty of moisture on the ground. Most snails like dampness. Look on the underside of leaves, or under rocks where snails like to hide out and avoid predators.
What do snails eat? (Leaves (fresh and decaying), stems, flowers, algae; some snails are herbivores. Other snails are carnivores). Snails have tiny mouths with tiny rasping teeth on a tongue.
Do we eat snails or other gastropods? (Yes, escargot, periwinkles, conches, and abalone for example).
What else likes to eat snails and slugs? (Birds and frogs, but discuss how these animals get the snail out of its shell).
How do snails move? (A band of muscles in the “foot” expand and contract to create a wave-like motion that moves the animal forward. The muscles are described as undulating. The movement on land or attached to something is called crawling or creeping. The foot is also used for digging and swimming).
Can they see (yes)? Hear (no)? Smell (yes)?
Is the shell the snail’s house? (Yes, and it provides protection. All the organs, like the stomach, are inside the shell, but the snail can also draw its head and the foot in to protect those as well).
How do they breathe? (Land and some freshwater snails have ONE lung. There is a hole in the body that allows them to take in air. Most aquatic snails have gills.) If observing a terrestrial snail, invite your child to see if the air hole on the side of its head opens and closes.
Studying snails in natural conditions can be a little difficult as they are mostly nocturnal. They can still be found, but it may be necessary to capture some for a closer observation. The exception is snails in tide pools or on a beach at the seashore. These can be observed at low tides in the daylight hours.
A hand lens will help to heighten observations, but one is not necessary. Sketching also helps to focus attention.
Examine animals that you have caught or purchased. They can be held or observed in an aquarium, a clear bowl or jar, or even a clear plastic sandwich container. If you are keeping a land snail for observation consider providing it with some moist soil as well as leaves, rocks, and sticks. If the snails were caught, perhaps consider returning them to the wild after investigating them.
As always, ask what your child sees, and follow up with additional questions to draw attention to other features or characteristics.
What is the shape of the shell? Can your child identify the apex or the center of the coils or spirals shell (also called whorls… such a great word!)?
Can your child tell where the “foot” is? What is the shape of the foot? (It is flat on the bottom).
If your child is examining a terrestrial snail, she should see slime. The slime (mucus) eases movement (it is a lubricant to reduce surface tension), protects the soft body, and creates suction so that the snail can crawl up things and even upside down. A gland that is behind the mouth produces slime.
What color is the animal and the shell?
Can your child identify tentacles (or eye stalks and feelers)? How many are there (should be two or four)? Sometimes, if lucky, your child will see the tentacles retract. Watch this video about half way through to see the tentacles re-emerge.
To observe how the tentacles work, place the snail on a piece of glass or another surface. With a brush or even with a finger, “paint” a smallish circle around the snail of diluted lemon juice, vinegar, or soapy water. Watch how the snail approaches that liquid. What do the tentacles do? (Don’t use very salty solutions or any kind of salt since this could unintentionally cause cell damage by accidental desiccation and harm the animal. Remember salting meat or fish is a way to dry it out – and would have the same effect on a snail.)
Can your child see an eye spot on the end of a tentacle (it won’t look like our eyes, but most can see at least differentiate levels of light and will have a vague impression of objects. There is also a possibility that they see color)?
Can your child find a mouth?
If you have snails in captivity, find a leaf that they may like to eat. Place the leaf on a piece of paper and trace around the edge leaving an outline of the whole leaf. Then, place it in the jar or bowl where the snails are. After the snails have nibbled at the leaf, place it back on the traced version. How much did the snails eat? Can your child see teeth marks? If you have or can visit somewhere with an aquarium, observe snails eat as they crawl over any algae that may be growing. They are grazing for food.
If you have the opportunity to visit an aquarium, look for gastropods in the various exhibits. They are a common way to control algae growth on the inside of display tanks so the glass stays clean for good viewing.
Some snails will have a trapdoor called an operculum that, if they withdraw into the shell, they can close behind themselves. Can your child find the door to the shell? (Operculum literally means “little lid”.)
What does the snail do, or how does it move? (Snails hibernate when the weather gets too cold or dry, pulling themselves into their shells closing the lid to the opening of the shell).
What does the snail or slug feel like? Touch the shell, what happens? Touch the foot or the slug, what happens?
Is there a smell?
Does it make a noise?
If brave enough to try a cooked version of a snail on a menu, what does a snail, conch or abalone taste like?
Compare and Contrast
Compare snails and slugs, or snails and whelks and limpets. What are the similarities or differences in how they look? After a close observation of a snail or slug, find pictures of other animals in the class gastropod and invite your child to discuss the differences he sees.
If you have a collection of shells or a collection of images, compare their size and color. Some snails are brightly colored (Why? It may be advertising the fact that they are poisonous if consumed.) Other snails are well camouflaged.
Categorize shells from largest to smallest or based on coloring or other markings.
If you have live snails, place several of them on a piece of glass or plastic that you can observe from underneath. You may need to build two “towers” of books or blocks with the glass/plastic placed on top. If your child can crawl under, he can observe the movement of the snails on top. Place them on a “starting line” and observe their movement or behavior, comparing their speed and the direction of their movement (straight, in a circle, wiggly).
If your child can’t watch the real thing, here is a good option:
Some snail shells are very fragile while others are stronger and solid. The snails need calcium carbonate to build a solid shell. In some areas this may be hard to find, resulting in a lighter and less solid shell. Snails will eat dirt for the calcium carbonate.
There are 60,000 – 80,000 species of gastropods. In the Animal Kingdom, only the class called Insects has more different species. These numbers may be too huge for a little one to grasp, but perhaps you can find the language to describe the fact that there are just so many different kinds of snails and slugs around the globe.
If you have access to a live snail your child can handle, a snail inside of an aquarium but easily seen from the other side, or perhaps even an empty shell, measure the size of the shell from top to bottom, from front to back. How big is the opening?
How long is the foot?
Count the number of spirals or coils on the shell.
If you can observe the movement of snails on glass (preferably from below or through a window or on the sides of an aquarium), consider making a mark on the glass or plastic with a non-permanent marker showing its location; and then waiting a pre-determined time interval, say a minute or two, after which you make another mark to designate where is now located. Measure the distance between the starting and ending marks. How far did the snail travel in a minute? Probably not very far, so you may want to choose longer time periods, as these animals are slow! It is pretty obvious why the expression “moves at a snail’s pace” is used for slow-pokes.
Estimate with your child how long the animal would be if uncoiled out of the shell. How might you figure this out?
Weigh a snail with its shell (or several similar snails and divide the weight observed by the total number to determine an average weight). Next, weigh an empty shell or several similar empty shells again determining the average weight. Subtract those two numbers to determine the approximate weight of the animal inside.
If you have a larger shell, such as a conch shell, point the upper tip down and fill it with water until full. Pour that water into a measuring cup to determine the volume of the interior of the shell. By looking at the amount of water in your cup, your child can begin to visualize how much room is in the shell. The bigger the shell the easier this is to do.
Repeat the “snail’s pace” observation but this time with a land snail on a loose pane of glass small enough to pick up and mark from below. After you have marked a starting location and placed the glass down horizontally, place a potential “food source” such as lettuce a small distance away as a goal. See if the snail can detect it and be motivated to move faster than if there is no food.
Here is a great experiment with snail slime:
Do snails produce more slime if they have to traverse a steeper slope? Test this hypothesis. You would think the answer is yes as they would need more slime to grip or stay attached to a steeper slope, or even if they were upside down. Place a snail on a piece of glass or plastic. Allow them to traverse it for an inch or two. Note the amount of slime. Next vary the slope of the plane, tilting the glass or Plexiglas. Note the amount of slime. If your child is having trouble seeing the slime, you can dust the glass where the snail has been with some flour. Repeat this process as often as need, continuing to vary the angle of the glass or turning it upside down and noting the amount of slime produced.
In examining slime, invite your child also take note of the snail’s movement in relation to gravity. They tend to move upwards.
If you have several snails at home, here are a series of investigations you can try with them. Please help your child be considerate of the snail’s comfort/discomfort, but variations in temperature, light and food sources occur in nature so, as long as the snail is not subjected to extreme variations, they should be able to cope.
Your child can try to observe the snails’ behaviors, or speed of movement, direction of movement, or eating behaviors under the following conditions.
- In different light conditions, or in dim light (if it is too dark your child can not see anything) versus under brighter lights (sunlight can be hot and dry their bodies out).
- In different temperatures. Place the snails for a short period (10 minutes) in the refrigerator. Place the snails in a warm (not hot) spot.
- In warm versus cooler water.
- In water versus on a dry surface.
- Offer different foods to see which the snails prefer. This could be a variety of leaves from out of doors, or leafy vegetables, or a combination. Record your results. This could even be set up as variations of the “snail’s pace” experiment to test which foods snails are really in a hurry to get to.
- Observe how a snail responds to light versus shadows. If you have a snail exposed to a light source (a lamp), cover the source slightly with an index card or your hand and watch what happens? Be careful to not overheat your snail.
- Observe movement on various surfaces. We have discussed snails on glass or Plexiglas. Place a snail on sand paper, gravel, or wood. Does their movement change?
With permanent markers of different colors, fingernail polish or a little paint, mark the shells of several snails and release them in an area in your yard. Wait an hour or two and try to find them. How far have they travelled? Where have they gone?
Elaborate and Glossary
The science of studying snails is called “conchology.”
Visit your library and find books about snails to share with your child. There are several great children’s books with stories including snails as the main character.
You may also want to look for books with interesting facts about these creatures. See if you can find information about how snail slime was used in medicine. The Ancient Greeks used it to treat ulcers and soothe a cough. Snails have been important to civilizations in other ways as well. They were a major source of protein for Roman armies. A group of marine snails known as “Murex” were the source of the intense non-fading Tyrian purple dyes as from far back as the time of the Phoenicians (1570 BC). They were still an important source of this naturally-occurring reddish-purple dye (known as “royal purple”) in the middle ages. Another group of marine snails called cowries have beautiful, porcelain-like shells more or less in the form of an egg, but flat on one side. Until as recently as the 1500’s shells of certain species were used as “shell-money” in some parts of the world. Cowries are often very beautiful and used extensively for jewelry in both past and present times.
If you get the question of how snails reproduce or what gender a snail is, this could be an interesting conversation if you think your child is ready. Most land snails and many marine gastropods are hermaphrodites, meaning they have both male and female reproductive organs, producing both sperm and eggs. So when they are fully sexually mature a partner can simultaneously play the role of both male and female. During mating, each snail fertilizes the other partner’s eggs. Because most animal species that are hermaphrodites cannot self-fertilize, partners are generally still required.
Gastropods lay eggs. Here is a video of baby snails hatching from their shells:
Ask your child to design the perfect snail shell or home.
Let your child’s imagination go wild and create their own fantastic nudibranch out of clay:
If you happen to live near or are visiting the seashore – go tide pooling to discover a wide variety of snails, slugs, and other gastropods.
Collect shells found on beaches, around the yard, or near a pond. If you are at the seashore or near a stream or pond, first determine if any given shell comes from a gastropod or a bivalve (clam-like mollusk). Keep the two groups separate. If your child is interested, label each shell as to when and where it was collected and try to determine what species or group it is as well.