Snails and slugs are more similar than they look. Both are gastropod mollusks, both have a radula with thousands of tiny teeth, and both move on a single muscular foot covered in mucus. The main visible difference is the shell — but the story goes deeper than that.
The Big Difference: The Shell
A snail has an external shell it can retract into for protection. A slug has no external shell (or only a tiny vestigial internal one). This single difference drives almost every other contrast between the two.
- Snail shell: Made of calcium carbonate, grows with the animal, provides protection from predators and desiccation
- Slug shell: Either absent or reduced to a small internal plate (the "saddle")
Full Comparison Table
| Feature | Snail | Slug |
|---|---|---|
| Shell | Yes — external, spiral | None (or vestigial internal) |
| Teeth | Up to 25,000+ on radula | Up to 27,000+ on radula |
| Body length | Varies (shell size varies more) | Generally longer relative to mass |
| Movement speed | 0.03 mph average | Slightly faster — up to 0.05 mph |
| Mucus production | Moderate | Heavy — more mucus needed without shell |
| Desiccation risk | Lower — can shelter in shell | Higher — needs damp habitat |
| Diet | Plants, algae, fungi, detritus | Plants, fungi, carrion, other slugs |
| Hibernation | Yes — up to 3 years | Less common — overwinter as eggs |
| Predators | Birds, hedgehogs, beetles, frogs | Same, plus easier to eat (no shell) |
Do Slugs Have Teeth Too?
Yes — slugs also have a radula with thousands of teeth. In fact, some slug species have slightly more teeth than garden snails. The radula works identically in both animals — it's a defining feature of gastropods, not just snails.
Which Is More Common in Gardens?
Both are extremely common in UK and European gardens. Slugs are often considered more damaging to crops because they can move faster, stay active in more conditions (not retreating into a shell), and are harder for predators to eat. Snails, by contrast, retreat into their shells during dry spells and may be less active during droughts.
Are They the Same Species?
No — snails and slugs belong to different families and genera, though both are gastropod mollusks. The two groups evolved separately, with slugs evolving from snail ancestors that gradually reduced and lost their shells over millions of years. This is called "shell reduction" and has happened independently many times in mollusk evolution.