Difference between Slugs and Snails

Published on October 31, 2016

Did you know that the mucous secreted by slugs and snails is essential to the survival of these gastropods (stomach walkers)? Keep on reading to find out more about these curious critters.

Definitions

Slugs vs Snails
It’s mating season for these two banana slugs

Slugs are usually land-dwelling, stomach walking invertebrates that do not have a shell. Some slug species have small shells they can’t crawl into, while others have an internal shell. Thus, a slug is simply a snail that does not have an external shell large enough for it to retract its soft body in.

Despite the lack of a protective shell, a slug can easily squeeze into tight spaces (e.g., cracks between stone slabs, wood boards) where natural predators cannot reach. Snails can quickly retract into their shell to protect themselves from predators.

Just like their shelled cousins, most slugs have two pairs of retractable tentacles on their heads, with the upper pair for sensing light and the lower ones for smelling. The bottom part of the slug is called a foot, which moves by muscle contraction, thus propelling the slug forward. Mucus secreted by the slug (which it uses to travel on) protects its foot from serious tissue damage.

Slugs are important in the ecosystem, as they eat decaying plants and fungi. The carnivorous variety feeds on dead organisms, including dead slugs and snails.

Snails
A beautiful garden snail

Snails are commonly known as land-dwelling, mollusk gastropods that carry shells on their backs large enough for these animals to retract into when needed. The word “snail” also includes other species of sea and freshwater snails that have gills for breathing underwater. Snails that do not have an outer shell are commonly called slugs. Land snails that do have an external shell but not big enough to retract into are called semi-slugs.

Snails can be found in farms, deserts, and even in the deepest parts of the sea. Land snails are more familiar to a lot of people, but marine snails make up most of the snail species. Many snail species can also be found living in fresh water.

The majority of land snails are plant-eaters and are treated as farm and garden pests. A large number of marine snails including a few land snails are omnivores that prey on insects and smaller sea creatures. Snails have about 27,000 tooth-like structures found on their ribbon-like tongue.

Slugs vs Snails

What’s the difference between a slug and a snail? The only major difference between these two gastropods is the presence of an external shell – snails can sneak back inside their shells at the first sign of danger, while slugs would have to find a small place to squeeze into, or puff themselves up to be bigger and harder as a defense mechanism.

Comparison Chart

Slug Snail
Does not have an external shell. Has an external shell big enough to fit its body in.
Usually grows up to 10 inches or 25.4 centimeters in length. Usually grows up to 15 inches or 38 centimeters in length.

Video

Check out this short YouTube clip talking about snails and slugs.