Snails! They’re cute, but most gardeners don’t get excited about slugs and snails eating their plants. They’re often treated as pests because snails feed on foliage and can remove tender leaves quickly. Some see little difference between snails and insects. But is a snail an insect?
Well, the short answer is no. They’re members of the animal kingdom, like bugs. But they’re in a different phylum altogether — the phylum Mollusca to be exact — unlike insects who are in the phylum Arthropoda.
And what’s the difference between a snail and a slug anyway? Is it just the shell? Whether they are or aren’t, and gardeners like them or not, they’re an important part of the ecosystem. They’re not furry creatures like mammals. And although they’re slimy, they’re not worms.
So let’s dive into an examination of just what slugs and snails are. We’ll take a little time to discuss how to deal with them in your garden, too. That way you can leave this piece with a little more knowledge about these closely related creatures.
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Classifying Slugs and Snails
There are so many different kinds of slugs and snails. There are land snails, freshwater snails, sea snails. These are all different species but they all are gastropods, or they’re placed in the class Gastropoda. The term gastropod originates from the Greek words for foot (poús) and stomach (gastros) which refer to their fleshy foot that sits on the underside of their bodies. So, by now we know that snails and slugs are, indeed, not insects, but gastropods.
Both slugs and snails are invertebrates in the class Mollusca which houses clams, mussels, and oysters. Interestingly, the phylum Mollusca encompasses squid and octopi too. But due to their intelligence, squid, and octopi are classed differently.
The mollusks called slugs and snails have shells that are different. Generally, the shells are composed of calcium carbonate. There are habitats where calcium carbonate is scarce, though. In this case, slugs and snails that live there have very thin shells or shells composed of a protein called conchiolin. Some may have adapted to environments that have no calcium carbonate at all. In this case, a shell may not be present.
Difference Between Slugs and Snails
The difference between snails and slugs has a lot to do with shells. Slugs are closely related to and evolved from the snail. Although it doesn’t look like it, they often have an internal shell, shaped much like the one on a snail’s back. As we mentioned in the last section, both may not have a shell at all in certain environments.
The other difference between slugs and snails is based on habitat, which we’ll cover (with a slimy trail!) later. But note these differences are based on behavior that directly relates to the environment they live in.
So, are snails insects? No! Are slugs insects? Nope. Turns out they are both different species of mollusks in the animal kingdom. But they’re not your typical mollusks like oysters, clams, and mussels.
Life Cycle of Snails
The overall trajectory of the mating habits and life cycle of these animals is largely determined by the environment. Because freshwater snails have different habits than land snails, we’ll cover the basic gastropod life cycle in general terms. Note that, unlike humans, they are a hermaphroditic animal and can carry both of the binary elements needed to reproduce.
The Developmental Stage
The most dangerous stage of a gastropod’s life is the stage from fertilization to hatching from the egg. Often snails and slugs mate and lay eggs in large numbers. Only a very small percentage hatch successfully. Other mollusks like clams lay eggs outside their shell to be fertilized.
Most slugs and snails have internal fertilization, and they’ll often lay what are called nurse eggs, which feed the viable offspring which have hatched from other eggs. In fact, cannibalism is common among many different species of land snails and freshwater snails. Once snails and slugs emerge from the egg, they’re considered larval hatchlings. Both slugs and snails are born with a shell (if their habitat supports one).
As the snail or slug body grows, they’re flying free out there on earth and sea. At least at first. They go through two larval stages: the trochophore and the veliger. The basic difference between the two stages is trochophores invertebrates tend to stay close to the hatching area, while veligers are large enough to move out of their original hatching station.
Between the larval and juvenile stages is metamorphosis, which occurs at the point in the larval stage where slugs and snails are too big to continue eating with their current anatomy. In this change, they develop an esophagus, which gives them the ability to begin eating plants. A snail or slug has to eat, right?
At this time, slugs and snails have what’s called an umbilicus. This may be present on the underside of a slug, or on the shell of a snail. Much like a belly button that humans have, there is no purpose for this feature. It’s simply a remnant of the beginning of their life in the egg.
Once the umbilicus is no longer present, slugs and snails are considered adults. And what do adult slugs and snails love to do? They love to eat! And science tells us they live for up to two years, barring an act of god… or spiders.
What Do Snails Eat?
Again, the food slugs and snails eat is largely determined by their habitat. Many species eat plants. Some species eat detritus or decaying matter. They thrive on whatever is there. Some are parasites, and some are carnivores who thrive off energy from eating other animals, like worms. They’re considered generalists, which feed off whatever plants and animals are around. This is why garden snails get a bad rep for being pests.
Typically those that eat worms and other animals (insects included) have teeth. And those that eat plants and detritus have teeth. What we’re saying here is that all snails have teeth and a jaw called a radula, which is used to funnel food into the snail’s esophagus for digestion.
Common Habitats of Snails
Snails compose about 80% of the mollusk class, which is a testament to how widespread they are. They live anywhere in the world, on land, and in water. Water-dwelling snails belong underwater because they are equipped with gills that allow them to breathe. Land-dweller slugs and snails belong on land. They don’t have gills to help them breathe when an area gets flooded. In that case, they must move.
Slugs and snails live under rocks, in soil, sand, leaves, lakes, rivers, and oceans. If there is food for a snail, it will live there. If there are lovely plants to munch on in your garden, or worms and insects to ingest, they’ll be there too. One thing they absolutely need is adequate moisture. Moisture is what allows a snail or slug to move. If they can’t move around gardens, forests, lakes, etc, they can’t respirate. The one exception is desert snails. They tend to leak moisture at much smaller rates than their relatives in more lush habitats.
How to Handle Garden Snails and Slugs
So now that we know a little bit about snail and slug life (they’re not insects! We know that), we can talk about handling them as pests in your garden. Maybe the weather has been really rainy, and snails and slugs are eating the heck out of your garden plants. Perhaps you’re looking for some answers as to how to deal with a plethora of pests. We have answers!
Well, one of the best ways to keep them off your plants is a snail and slug bar in the form of a beer trap. Slugs and snails can’t resist the lure of the sauce, much like some people you might know. The difference between them and humans, in this case, is they drown in the beer.
Another great and organic method of dealing with slug and snail pests is copper tape. Place a perimeter of tape around the base of your plants, raised beds, and containers. Pests like slugs and snails don’t like the way copper feels on their tender invertebrate bodies, and they avoid it. This is a great way to deter them from eating your plants and avoid killing them at the same time.
Snail And Slug Bait
If you don’t have time for deterrence, and you just need them gone, there are plenty of slug baits on the market. These baits make it so you only have to put them out once per season. Sounds great, right? There are plenty of organic options for slug bait if you’re trying to avoid chemical additives to the garden. Most OMRI-rated snail and slug baits are comprised mostly of iron phosphate and are pet safe as well as child safe. The iron decomposes and provides nutrients to plants in the future.
Their Benefit to the Ecosystem
Unless they are being pesky, snails and slugs are important members of the natural world. They feed on detritus and help break down plant matter, which helps you, gardener! Some are compost pile buddies and assist in clearing and processing detritus that you need for your garden. They’re also a great source of food for other animals. Toads, worms, beetles, and birds all eat snails and slugs.
Recently, however, there has been a problem with giant African land snails getting away from their respective owners and causing a lot of ecological damage. They eat any kind of plant they can, and they also carry worms that cause meningitis in humans. If you find one, you’re asked to photograph and report it to the USDA Invasive Species Unit.
Frequently Asked Questions
Q: What is a snail classified as?
A: Are snails insects? No! They (and slugs) are classified as mollusks. More specifically, they are gastropods.
Q: Do snails have a gender?
A: They are hermaphrodites, which means they carry both reproductive elements inside of them.
Q: How long do snails live for?
A: Snails live for up to two years.