10 Interesting Facts About Slugs

Slugs are more than just garden pests! These slimy mollusks play a vital role in ecosystems around the world. Their unique biology enables them to thrive in many environments. Discover 10 fascinating facts about the secret lives of slugs!


The word “slug” conjures up images of the slimy, shell-less gastropods that munch on garden plants. But there’s much more to these soft-bodied invertebrates. Over the centuries, slugs have evolved incredible adaptations for survival. They fill an essential niche in nature by recycling nutrients and serving as food for birds, mammals, and other creatures. Read on to uncover some captivating truths about these misunderstood mollusks!

1. Slugs Generate Slime for Protection

Closeup of a yellow banana slug at Olympic National Forest, Washington
Closeup of a yellow banana slug at Olympic National Forest, Washington

A slug’s body is 80-90% water, making it prone to desiccation or drying out. To prevent this, slugs secrete slime composed of mucopolysaccharides 1. This moist, slippery coating helps retain moisture. It also protects slugs from abrasive surfaces and harmful microbes. Some slug slime contains deterrent chemicals to hinder predators. Its gel-like texture enables slugs to adhere to vertical surfaces while moving upside down![Slug clinging upside down]

2. Slugs Have a Rasping Tongue with Thousands of Teeth

The slug radula is a minuscule tongue covered in rows of tiny, chitinous teeth – up to 27,000! It works like a file, rasping off particles of food. The radula scrapes algae from rocks and nibbles decaying plant matter. As the teeth wear down from use, they’re continually replaced. This amazing, self-sharpening tongue helps slugs eat all kinds of foods.

3. Slugs Can Self-Amputate for Protection

When attacked, some slugs self-amputate part of their body in a process called autotomy. For example, the spotted leopard slug can detach up to a third of its tail. The severed portion writhes wildly, distracting the predator while the slug escapes. The missing tail section later regenerates. Autotomy allows slugs to survive predation. It’s a fascinating adaptation!

4. Slugs Have Four Retractable Sensory Tentacles

On their heads, slugs have two pairs of retractable tentacles used for sensing their environment. The upper tentacles detect light and motion. The lower tentacles provide the senses of smell, taste, and touch. Slugs can extend these tentacles separately, allowing them to simultaneously see and smell surroundings. The tentacles are very sensitive and quickly withdraw when touched.

5. Some Slugs Hunt Other Slugs

A black slug in the forest of Mount Aizkorri
A black slug in the forest of Mount Aizkorri

Most slugs eat decaying plant material, algae, fungi, and carrion. But some species have more sinister diets. The gray field slug hunts and eats other slugs and snails. It follows slime trails to find prey. The snake-skin slug of South Africa also feeds on other slugs. These carnivorous slugs use their raspy radula to drill into shells and devour the occupant inside.

6. Slug Slime Has Medicinal Uses

In some cultures, slug slime has been used to treat ailments. The mucus contains chemicals with antimicrobial and anesthetic qualities. The native peoples of North America used slug slime as a remedy for toothache. In Italy, slug mucus was applied to treat gastritis and stomach ulcers. Modern research has revealed the bioactive compounds in slug slime have potential pharmaceutical applications.

7. Slugs Are Hermaphrodites

Most slugs possess both male and female reproductive organs. When they mate, they fertilize each other through internal fertilization. Slugs with compatible genitalia intertwine and exchange sperm. In some species, the penis detaches after mating! Slugs can also self-fertilize if mates are unavailable. Their hermaphroditic biology maximizes reproductive success.

8. Slug Eggs Can Survive for Years


Slug eggs are very hardy. They resemble small white pearls, laid in clutches in moist soil. The eggs have a protective membrane that prevents desiccation. They can endure cold winters and hot summers in a dormant state, only hatching when conditions become ideal. This resiliency allows slug populations to persist. A single slug can lay up to 500 eggs per year 2!

9. The Slug Foot is a Powerful Muscle

A slug’s flattened underside is called the foot. This muscular organ ripples in waves to propel the slug. Contractions begin at the rear and move forward. Coupled with slippery mucus, this motion glides slugs along effortlessly. Specialized muscles on the foot’s underside power the rippling. This muscle tissue makes up most of the slug’s body mass.

10. Slugs Lack an Internal Shell

Unlike snails, slugs lack a complete, external shell. But they aren’t shell-less. Most slugs have an internal vestigial shell, concealed within their bodies. In some species, the shell is reduced to a thin calcium plate. Other slugs have a partial external shell. Shell reduction allows slugs flexibility to squeeze into tight spaces snails can’t access.


Slugs are astonishingly adapted for life on land and in the sea. Their mucus, raspy tongues, and retractable tentacles enable these gastropods to thrive worldwide. Slugs fill vital ecological roles, and their unique biology makes them endlessly fascinating. Next time you see a slug, take a moment to appreciate the ingenuity of its evolution!


  1. https://www.sciencedirect.com/science[]
  2. https://www.soilassociation.org/media/16046/factsheet-slugs-june-2018.pdf[]