FaunaHub

Slug (class Gastropoda (shell-less))

InvertebrateMolluscGastropod

Leopard slug (Limax maximus) showing its mottled grey body.

Leopard slug (Limax maximus).

Image: Michel Langeveld, CC BY-SA 4.0, via Wikimedia Commons.

Overview

Slugs are soft-bodied gastropod molluscs — essentially snails that have lost or greatly reduced the external shell. They glide on a single muscular foot, leave a mucus trail, and carry sensory tentacles on the head, with eyes at the tips in land species. The reference shown here is the leopard slug (Limax maximus), a large, mottled species.

Losing the heavy shell lets slugs squeeze into tight, damp spaces that a shelled snail could not reach, though it leaves them more exposed to drying out and to predators.

Note: “slug” covers many unrelated lineages that have independently lost their shells, so habits vary. Treat details as approximate and verify against authoritative sources.

Habitat & Range

Land slugs live in moist habitats — gardens, woodlands, leaf litter, and under stones and logs — and are most active at night or after rain, when humidity is high. There are also many sea slugs in the oceans. Land slugs avoid dry, hot conditions, sheltering in damp hiding places by day.

Diet

Most land slugs are omnivores or detritivores, feeding on living and decaying plants, fungi, algae, and other organic matter, which makes them important recyclers in the soil. Some, such as the leopard slug, will also eat other slugs. Like snails, they feed using a rasping, toothed radula.

Behavior

Slugs move slowly on a film of mucus and rely heavily on that mucus to stay moist, grip surfaces, and deter some predators. They are mostly nocturnal. Many are hermaphrodites with remarkable mating behaviour — leopard slugs are famous for mating while suspended together from a thread of mucus. In dry conditions slugs retreat to damp shelters to avoid water loss.

Human Interaction & Conservation

Slugs are often seen as garden pests because some species damage seedlings and crops, but many are harmless recyclers of decaying matter and part of healthy soil ecosystems, and they are food for birds, hedgehogs, and other wildlife. Management is best done with their ecological role in mind. Consult authoritative sources for specifics.

More photos of the slug

A leopard slug crawling across the ground.

Leopard slug (Limax maximus).

Image: Rylosims, CC0, via Wikimedia Commons.

Frequently Asked Questions — Slug

Is a slug just a snail without a shell?
In broad terms, yes — slugs are gastropod molluscs closely related to snails that have lost or greatly reduced the external shell. Several different snail lineages have independently evolved a slug-like, shell-less form, so "slug" describes a body plan more than a single group.
Are all slugs garden pests?
No. While some slugs do damage seedlings and crops, many feed mostly on decaying plant matter and fungi, helping recycle nutrients in the soil. Slugs are also important food for many animals, so they play a useful ecological role.
Why are slugs so slimy?
The slime is mucus that lets slugs glide, grip surfaces, and — crucially — stay moist, since without a shell they are very prone to drying out. The mucus can also make a slug harder for predators to handle and helps it move across rough ground.
What do slugs eat?
Most land slugs are omnivores or detritivores, eating living and decaying plants, fungi, and algae, and some also eat other slugs. They feed with a radula, a toothed ribbon that rasps food into the mouth.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.