Slugs and Snails are both gastropods under the higher classification of Mollusca. The main difference between them is the most visible one. Snails have hard coiled shell on the outside of their body. Slugs have a soft shell that you usually cannot see, underneath their body.
Let’s take a deep dive into the complicated world of gastropods. But don’t worry; I’m about to make life a lot simpler for you.
What is a Slug?
When talking about “slugs”, one would normally assume that you are talking about land slugs. Many slugs are classed as pests, eating through plants in the garden until there is basically nothing left.
There are sea slugs, too. They live in the sea, obviously.
There are also semislugs, which have what is known as a reduced shell. This is too small for them to be able to recoil into, however. That’s what differentiates between snails and semislugs: snails can recoil back into their coiled shells. Semislugs can’t. The reduced shell isn’t big enough.
True or False: The Slug Has a Small Internal Shell?
True! (Sometimes.)
Many adult stage slugs have what is known as a vestigial shell – a small internal shell used to store calcium. This is a remnant of the evolutionary trail. Both snails and slugs have the same key ancestors, way back in history.
Having an internal shell doesn’t turn a slug into a snail, however. Being able to store calcium doesn’t give the slug the option to suddenly grow a shell.
What is a Snail?
A snail looks like a slug with a home – the shell on its back. There are snails that live on land (land snails) as well as sea snails, freshwater snails, and semi-aquatic snails. The latter can live in water and on land.
It is quite rare for people to eat slug for dinner, but there are more than a few cultures known for eating freshwater snails, sea snails and land snails, known as escargot. French people, for example, are infamous for eating escargot with butter, garlic, and other tasty herbs. The word ‘escargot’ is French in origin.
Are Slugs Snails Without Shells?
No, despite what you may have read on the internet, slugs aren’t just land snails without an external shell. An adult stage slug will not develop a snail’s shell.
The shell might be the main difference between the gastropod mollusk types, but it’s definitely not the only one.
Slugs are a species, class, and a family all their own, with characteristics that set them apart from snails. There are similarities between a snail and slug, but there are also a host of key differences – appearance, defense mechanisms, diet, habitat, anatomy, reproductive activity, and more.
Can Slugs and Snails Mate?
Asking if slugs and snails mate is a little bit like asking if gorillas and chimpanzees can mate.
Slugs and snails are both slow moving gastropod mollusks, and they both have what is known as a muscular foot. A muscular ventral foot, to be exact. They move by contracting and releasing it, just like a large muscle. Aside from that, however, the two mollusks are biologically different.
Snails and slugs are completely different species, from a different class and family, with different ancestors. For that reason, snails and slugs can’t and won’t come together to mate.
What would you call them if the slug and the snail could mate, though? Slail? Sluil? Snaug?
How Are Slugs and Snails the Same?
Many slugs and snails are the same in a few ways, but not all. Both snails and slugs move very slowly, and they are both known as “stomach foot” in Greek. The word – Gastropod – is made up of Greek words for stomach and foot.
Both creatures are from the phylum Mollusca; and from the class Gastropoda.
Fun Fact: There are lots of other animals within the Mollusca family – squid, octopus, clam, and cuttlefish, to name just a few.
Here are a few of the other ways in which slugs and snails are similar:
Appearance
It could be said that the two mollusk types look the same, but they don’t, really. You can tell the difference between the two. The snail has an extra part – the exterior shell, often coiled in shape. The other mollusk, doesn’t.
The body of the mollusk looks the same, known as the foot. It has a flat bottom. Neither creature has a backbone, making both slugs and snails invertebrates, and they both breath air using an organ called a pallial lung. No difference there.
The head and basic anatomy is the same in both the snail and slug, too. Two external tentacles poke up, eyes on stalks. These tentacles are used in chemosensory processing.
Size
The largest Achatina achatina individual, also known as Giant African snail, had a body (foot) of over 15 inches. Most species aren’t quite that large, of course.
The biggest slug is Limax maximus, which can grow up to 10 inches in length.
Diet
Most snails and slugs eat similar diets, but this isn’t the case for all of them. A slug’s diet is mostly made up of:
· Fungi
· Carrion (decaying animals/dead animals) and other ground debris
· Algae/biofilm
· Earthworms
· Other gastropods
· Garden vegetables and flowers
A snail will eat the same foods, including other snails and slugs. Most snail species are “generalist” feeders, just like slugs. That’s why they can be your gardeners’ worst nightmare, the pests eating plants at an astonishing rate. Snails and slugs move slowly, but they don’t eat the same way.
There are “specialist feeders” in the snail world. A specialist feeding snail will have a diet specific to native habitats – certain algae or plant types.
Feeding Behavior
Snails tend to feed at night whereas slugs feed all the time. If there’s a steady supply of plant life and/or food, they’ll carry-on eating. That’s how they decimate a vegetable patch and other plants in no time.
There are a few exceptions, such as the Kerry slug. This species hides during the day and increases movement at night to feed.
Snails and Slugs: Habitat Types
Both the slug and the snail can be found all over the world, in all sorts of different habitat types.
Elephant snails are wild snails found in shallow reefs around Western Australia, New Zealand and Tazmania.
The Giant African land snail, on the other hand, lives on land. It is actually classed as an arboreal snail species, which means that it spends a lot of its time in – as you might have guessed – trees. It is also one of Florida’s most problematic pests.
The black slug, also known as Arion Ater L., large black, European black, or black arion slug, is found all over the world. It is native to Europe, but can be found, as an invasive species, in the US, Canada, Australia, Spain, and other places. Where it is invasive, it competes with native snails and other snail and slug types for food and other resources.
How Are Slugs and Snails Different?
These two mollusks are different in more ways than you might think, and it doesn’t just come down to the snail’s hard shells. As well as biological differences, slugs and snails can also be different in terms of behavior, habitat choices, and a lot more.
Let’s take a look at some of the ways in which slugs and snails are different.
Slug vs Snail: Body
The body, also known as the foot, is different in each of these gastropod mollusk types. It might look the same, squishy, and with a mantle, but there is quite a big difference between the two.
A slug does not have a coiled shell. Because of this, the body tends to stay relatively straight, with little coiling movement. When threatened, it stiffens and hardens itself, and release mucus.
A snail, on the other hand, has an exterior shell made of calcium, large enough to contain the body. When threatened, the defensive movement includes recoiling back into the shell.
Slug vs Snail: Aggression
Snails are peaceful and docile creatures, but slugs can be quite the opposite. It is not uncommon for slugs to attack each other in competition for food, mates, territories and more.
If there were to be a fight* between the average snail and the average slug, the shell-less slug has the potential to win due to sheer aggression.
*No snails or slugs were harmed in the making of this article… obviously.
Slug vs Snail: Best Defenses
The snail’s shell works as defense against predators. They can retreat into the safety of the coiled shell, essentially blocking themselves off from whatever is trying to attack them, without worrying about finding hiding spots on the ground/in the water.
There are animals that can get around outer shells, but for the most part, it works as a decent defense mechanism.
Slugs, on the other hand, do not have protective snail shells. They produce a thick mucus from epithelial cilia on the foot that tastes bad and feels sticky. They don’t need an outer shell.
Slugs will also slither off into cracks and crevices in rocks, boulders, and other habitat debris. A snail won’t always be able to fit into those same spaces because of the bulky shell.
One species – Kerry slug or Kerry spotted slug (Geomalacus maculosus) can roll itself up into a ball in defense along with the production of mucus. It is the only slug species observed rolling itself up into a ball.
Most other species of slug contract their bodies when they come under attack, as a form of defense. This causes them to go hard and appear unappealing to feed on. At the same time, they retract the head.
Land Snails and Slugs: Which is Fastest?
Snails are usually slower than their shell-less counterparts, because the external shell slows them down. Slugs are slightly faster because they don’t have a shell adding extra weight.
In this round, the humble slug wins. (But only by a fraction; they travel at pretty similar speeds for the most part.)
Which One Lives Longer – Snails or Slugs?
Most snail species will live for around two to three years. There are exceptions to that rule, of course; some people have had the same snail in home aquarium setups for four, five, six years and beyond. Generally, though, three years is seen as a ‘good’ age for a snail to reach.
Most slug species will live for up to five or six years if the conditions are ideal.
Are there Any Edible Slugs?
Yes, there are edible slugs.
Most people know that snails are edible, but not a lot of people know that there are edible slug species in the gastropod mollusks family, too.
The banana slug, found in North America and from the Ariolimax genus, is eaten in some places to this day. Northern California’s Russian River is the location of an annual contest in which these slugs are cooked and recipes featuring them are shared.
For health and safety reasons, it is not recommended to cook and consume slugs, especially the ones you’ll find in your back garden. They can carry disease-causing pathogens and parasites that you likely won’t want to pick up!
Slugs vs Snails: Conclusion
Snails and slugs can’t come together to reproduce, nor do they look the same when you really think about it. A snail isn’t a snail without that exterior shell, after all. And a slug isn’t a slug if it has a shell. (Mostly.)
Snails and slugs are not the same.
Similar, yes; but most definitely not the same. There are huge, fundamental differences between them, and they are large enough to set the two gastropods apart completely!
