Difference Between Slugs and Snails

Grape Vine Snail

Slugs vs Snails

1. Classification
The taxonomy of both slugs and snails is the same in that they both belong to the Mollusca phylum and the Gastropoda class. However, this is where they diverge slightly. The suborders within the Gastopoda class that are comprised of slugs include Orthurethra and Sigmurethra, and these are both comprised of many families or superfamilies.i Snails are in the same Gastropoda class, but they lie in the superorders of Neritimorpha, Caenogstropoda, and Heterobranchia, all of which have many families or superfamilies within them.ii

2. Appearance
The most obvious difference between slugs and snails is that the snail has a shell and a slug does not. Aside from this, they both are known for their soft body, which can come in an array of different colors. When a snail is moving, most of its body is actually extended outside of its shell as it has a very large retractor muscles which moves the rest of the snails body and shell. There is always part of the snail that does remain inside the shell, which is called the visceral sac, and is covered by a mantle and possibly, a breathing hold called the pneumostome. Snails can sometimes hatch with a shell already on them, or sometimes the shell will grow and harden as they grow. The shell color and appearance is one of the key indicators of species and they come in a wide variety of patterns and colors.iii Slugs are typically described as a ‘snail without a shell’ and it is true that there are many similarities between the two. Although it should be noted that some slugs have retained a small shell, typically a remnant of their evolutionary former shell, but some have no shell at all. If they do have one, it is referred to as a vestigial shell.iv Their soft body can be a gray, brown, black or even yellow color. Also like snails, slugs have two antennae, known as tentacles or feelers, on their head. These are used to sense light and also provide a sense of smell. They are retractable and can be regrown if the slug loses one. They also have a mantle and a pneumostome and a large foot that helps them move, similar to the retractable muscle of the snail.v A slug also has a tail behind the mantle and a ridge that runs across the middle of the tail called a keel. The keel may run across the entire tail or just the final part.vi

Slug

3. Habitat
Slugs can be found in most climates across the world as long as they have moisture. They even live in marine environments, and are known as sea slugs. However, the more common terrestrial slugs tend to prefer residing near human-made structures, especially gardens, farms, trash dumps and compost piles. They may also seek shelter in places such as underneath flower post, wood pieces, leaves and other items during the day.vii The fact that their bodies are so soft and they lack a shell makes it easy for them to squish themselves into various hiding places that a snail might not be able to use. Like slugs, snails can be found in habitats across the world, including in the ocean as well as in freshwater. And while they prefer moist environments, there are some species that even live in deserts, though they might spend more time in their shell-an action that a slug would be incapable of doing. They also enjoy living near human activities, including by gardens and even underground. They tend to come out when it is raining.viii

4. Food source
Snails have been a food source for humans for a very long time. And in European, especially French, cuisine they are considered a delicacy known as escargot a la Bourguignonne. Aside from that, they remain a key source of protein for many people in the poorer regions of the world. Countries that regularly consume either sea or land snails include Spain, Philippines, Morocco, Nigeria, Algeria, Cameroon, France, Italy, Portugal, Greece, Bulgaria, Belgium, Vietnam, Laos, Cambodia, Cyprus, Ghana, Malta, southwestern China, Northeastern India and parts of the United States. Sometimes, the eggs of a snail can be eaten similar to how caviar is eaten. When preparing snails, it is best to wait until a rainy period when they come out from hibernation and release most of their mucus. After they are prepared for cooking, their texture is typically slightly chewy.ix Unlike snails, slugs are very rarely used as a food source. There are a few instances, such as with the larger banana slugs, in which they might be eaten, but for the most part, they are not considered an acceptable food source and may actually be a health concern if consumed. Humans have been known to develop cases of meningitis when accidentally eating raw, live slugs on improperly cleaned vegetables or consuming improperly cooked slugs. They can also be a source of parasitic infection in humans.x

5. Breeding
Terrestrial snails and slugs are unique in that they are mostly hermaphrodites, meaning that they have male and female reproductive organs. When they reproduce, it results in both mates becoming impregnated. However, there is a difference in the amount of offspring both can produce. It is common for a snail to carry up to 100 eggs at a time.xi This is over three times what the average slug is capable of. They typically only lay approximately 30 eggs after they have been fertilized.xii

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