Difference Between Slug and Snail

The main difference between slug and snail is that the slug is a type of snail that lacks a conspicuous shell whereas the snail is a shelled gastropod whose shell is large enough to completely retract the whole animal into it. Furthermore, the movement of slugs is more maneuverable and compressible while the movement of snails is less maneuverable and compressible. 

Slugs and snails are two types of gastropod mollusks with a ventral foot. They are considered as pests by gardeners since they eat all plant materials such as fruit, flowers, leaves, stems, and roots. 

Key Areas Covered 

1. Slug
     – Definition, Characteristics, Behavior
2. Snail
     – Definition, Characteristics, Behavior
3. What are the Similarities Between Slug and Snail
     – Outline of Common Features
4. What is the Difference Between Slug and Snail
     – Comparison of Key Differences

Key Terms 

Coiled Shell, Mantle, Gastropods, Slug, Snail, Tentacles

Slug – Definition, Characteristics, Behavior 

Slug is a terrestrial gastropod that lacks a shell. However, some slugs may have reduced shells or an internal shell. Slugs belong to different families along with snails.

Figure 1: A Slug

The main parts of the body of a slug are described below. 

• Tentacles – The two, retractable pairs of tentacles are the optical tentacles and sensory tentacles of smell.  
• Mantle – The genital opening and the anus can be found in the saddle-shaped mantle behind the head. The respiratory opening or the pneumostome occur on the right-hand side of the mantle. 
• Tail – Th part of the body behind the mantle 
• Keel – A prominent ridge running over the back 
• Foot – The flat bottom side, which helps the slug to move through rhythmic waves of muscular contractions.  
• Vestigial shell – An internalized shell used as the calcium storage shell 
  

  Figure 2: Slug Anatomy

Slugs feed on various organic materials such as leaves, lichens, mushrooms, etc. Therefore, some species of slugs are considered agricultural pests. When threatened, slugs roll their body and contract the tentacles. 

Snail – Definition, Characteristics, Behavior 

Snail is a gastropod with a coiled shell. The shell is large enough to retract the whole animal into it when threatened. There are sea snails, freshwater snails, and landsnails. The largest snail is the Giant African snail.

Figure 3: A Snail

Snails also have the same anatomy as a slug. The lung, liver, stomach, kidney and the heart occur inside their shell. 

Figure 4: Snail Anatomy

Most snails are herbivores while a few such as land snails consume other terrestrial snails. 

Similarities Between Slug and Snail 

• Slug and snail are two types of gastropod mollusks with a ventral, muscular foot. 
• Both belong to an informal group called pulmonates. 
• They do not have a backbone, so they are invertebrates. 
• Also, they both secrete mucus on the ground, which helps them to move. 
• Both breathe air by a pallial lung.  
• They have two pairs of tentacles and compound eyes.  
• Further, they are slow-moving creatures. 
• Both hide in dry conditions to prevent the loss of moisture from the body. 
• They are commonly hermaphrodites. 

Difference Between Slug and Snail 

Definition 

A slug is a tough-skinned, terrestrial mollusk that typically lacks a shell and secretes a film of mucus for protection while a snail is a mollusk with a single spiral shell into which the whole body can be withdrawn. 

Shell

The most distinguishing feature of a slug is the absence of an outer shell while snails have a large, coiled, exterior shell. 

Habitat 

Slugs are terrestrial animals while snails can be either terrestrial or aquatic animals.

Habitat and Behavior 

Also, slugs can squeeze into many different habitats that snails cannot while snails often take refuge inside their shell. 

Movement 

Furthermore, the movement of slugs is more maneuverable and compressible while the movement of snails is less maneuverable and compressible. 

Color 

Comparing the appearance, the slugs can be black, grey or yellow while snails are mainly grey-colored with a black, brown or white color shell.  

Length 

Moreover, the slugs can be up to 15 inches long while snails can be up to 10 inches long.  

Lifespan 

Looking at the lifespan, the slugs can live more than 6 years while snails can live up to 2-3 years. 

Human Diet 

Slugs can be used in the human diet while the most popular snails in the human diet are land snails. 

Examples 

Some examples of slugs include field slug, garden slug, keeled slug, large black slug, etc. while some examples of snails include garden snail, banded snail, strawberry snail, etc. 

Conclusion 

Slug is the gastropod without an external shell while snails have a coiled shell on top of their body. Both slugs and snails share the similar anatomy. One of the characteristic features of both slugs and snails is the muscular foot, which aids the movement. The main difference Between slug and snail is the presence of an external shell. 

Reference:

1. “Slug and Snail Anatomy.” All About Slugs, Available Here
2. “Anatomy.” The Snail Wrangler, Available Here

Image Courtesy:

1. “Slug crop-aspect” (CC BY-SA 3.0) via Commons Wikimedia 
2. “Slug parts” By en:User:Billlion – Flipped and relabeled image so that pneumostome is on right side of body. (CC BY-SA 3.0) via Commons Wikimedia 
3. “Flickr – Per Ola Wiberg ~ mostly away – Snail ~ 07-07-07 (3)” By Per Ola Wiberg from Ekerö, Sweden – Snail ~ 07-07-07 (3) (CC BY 2.0) via Commons Wikimedia 
4. “Snail diagram-en edit1” By Original by Al2, English captions and other edits by Jeff Dahl – Own work (CC BY-SA 4.0) via Commons Wikimedia