Gastropod mollusc that lacks a shell.
A slug is a gastropod mollusc (class Gastropoda), similar to snails but lacking an external shell. Most (but not all) slugs have an internal vestigal shell which is only visible with dissection.
Slugs are common in wet temperate zones (eg. the Pacific North-West and the UK). With wet, slimy bodies, they are prone to drying out (dessication) and will retreat to damp hiding places during dry weather. As with snails, slugs travel on a mucus layer. A night of active slugs can be readily seen in the garden by the muscus trails that have been left behind.
Slugs eat green vegetation and can be a large problem in areas where they are common.
Control techniques include applying a substrate (eg. eggshells or diatomaceous earth), bait ("slug pellets"), beer traps, salt (leads to dessication through osmosis), and encouraging predators (eg. toads).
Slug muscus can be used to treat a number of skin conditions including dermatitis, inflammation, and acne. An old Italian treatment for stomach ulcers, was to swallow a slug whole. Now that peptic ulcers are better understood, it is thought that this treatment is unlikely to work.