Slug vs. Snail: More Than Shell vs. No Shell (But Not Much More)

Asian Tramp Snail — Did you know that snails and slugs have tentacles with eyes at the ends? Image by Adam Young / Getty Images

At first glance, slug vs. snail might seem like a case of one just missing a shell. And in a general sense, that's not far off.

Both slugs and snails are gastropod mollusks, part of a huge class of animals that includes more than 60,000 species.

The Main Difference: The Shell

Brown garden slug — A snail's shell is pretty prominent, so you can deduce on sight that this is a slug. Roger W Downes Photography / Getty Images

Snails carry a large exterior shell they can completely retract into. Most snails — including land snails, freshwater snails and sea snails — use this external shell for protection and moisture retention. Slugs lack this feature.

Many slugs have either a reduced shell or an internal vestigial shell that offers little defense. This might sound like a disadvantage, but slugs benefit from the flexibility their missing shell gives them. They can squeeze into tighter hiding places, a key survival advantage in habitats full of predators.

Similar Features, Different Strategies

Slugs and snails share similar anatomy: a soft, moist body, a head with two pairs of slender tentacles, and the ability to produce slime trails. These slime trails help them move and protect their undersides from rough surfaces.

Their diet also overlaps. Both feed on organic matter, dead animals and living plants.

Gardeners often notice slug damage on flowers and garden plants, just like they do with snails. However, slugs can be more problematic since their lack of a shell makes them more active in tight or moist garden spaces.

Predators and Pest Control

Bird with a snail in its beak — It's tough out there for snails (and slugs). Sandra Standbridge / Getty Images

Both slugs and snails have natural enemies. Birds, toads, snakes, beetles and turtles all prey on these gastropods.

Because they can become garden pests, gardeners often use non-chemical methods to control slugs and snails. Dropping them into soapy water, encouraging natural predators and removing their eggs are common biological control tactics to address or repel slugs.

In some cases, gardeners choose specific plants that deter slugs or improve habitat for slug-eating insects. This approach helps protect gardens without relying on chemicals.

Diversity in the Gastropod World

There are thousands of snail species and slug species worldwide. Slugs found in gardens are usually a few inches long, while the largest snail species can have shells over 12 inches (30 cm) across.

Most gastropods develop a shell in the early stages of life, but many slugs lose the shell by adulthood.

Whether coiled shells or no shells at all, gastropods have adapted to survive in diverse environments, including deep oceans to backyard gardens.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.