Limax maximus Linnaeus (1758)
Giant garden slug

The word "slug" describes a body shape rather than a group of species with a common ancestor. Essentially, "slugs" are "snails" that have either lost their shells or are in the process of losing their shells. This has happened many times in snail evolution. The most obvious "slug groups" are the the sea slugs and the land slugs.

The sea slugs (order Opisthobranchia) contain not only the spectacular nudibranchs, which have all lost their shells, but also primitive groups such as the Cephalaspidea or Bubble Shells which have snail-like members with heavy external shells (Pupa sulcata) as well as members with brightly coloured bodies and no shell (Sagaminopteron ornatum).

The land snails (order Pulmonata) have on a number of separate occasions evolved "slugs". One common northern hemisphere family, the Limacidae, have cursed most of the temperate world with pests such as Limax maximus. The name "pulmonata" refers to their development of the mantle cavity into a lung for airbreathing. The large hole visible in the accompanying photo below, is the pore (pneumostome) through which air moves in and out of the lung.

The marine snails (previously ORDER Prosobranchia)are no longer considered to be a single group with a common phylogenetic ancestry. Amongst these animals, slugs have evolved many times. The Australian Elephant Slug, Scutus, in fact retains a shield like shell (white streak in photo) which is hidden beneath flaps of skin.

Taxonomy
Name:	Giant Snail or Garden Slug
Category:	Molluscs
Phyllym:	Mollusca
Class:	Gastropoda
Subclass:	Mulmonata
Family:	Limacidae
Genus:	Limax
Species:	maximus
Authority:	Linnaeus

Description: 

A large slug (extended length, 100 mm or more), typically yellowish grey or brown spotted or striped with black, or uniformly dark brown; spots often coalesced into 2 or 3, often interrupted, pairs of lateral bands; mantle with spotted or mottled brown, well anterior and  with its posterior edge somewhat angular from above, skin of the mantle having a pattern of fine concentric wrinkles, somewhat like a fingerprint, with this pattern centred on the midline of the mantle; pneumostome behind the middle of the mantle; head pale, tentacles reddish brown; foot fringe pale; keel incomplete, near the tip of the tail only; tail tapering more or less gradually to a point; mucus colourless, sole creamy white. Internal shell oblong with the nucleus terminal and left of centre.

Similar Species: 

Limax maximus is comparable in size to the native, coastal Banana Slug (Ariolimax columbianus) (Gould, 1851), but has a wrinkled mantle and different colour markings.

Range: 

Europe, Asia Minor and Algeria. Introduced North America, South America, Australia, Hawaii and elsewhere (Pilsbry 1948).

Habitat: 

Limax maximus occurs in gardens, fields and woods; in damp, shaded places, under rocks, wood and vegetation.

How Slugs Copulate

Pictured are two Great Slugs (Limax maximus) in the throes of passion. Michael Martin, John May, and Rosemary Taylor describe their act as follows in "Weird & Wonderful Wildlife": 

"After crawling up an overhanging branch or wall, these hermaphroditic creatures circle each other for 30-90 minutes while exchanging mutual caresses with their tentacles and secreting a great quantity of mucus which eventually forms into a twisted patch of glue-like consistency some two inches in diameter. The slugs then entwine themselves corkscrew fashion, detach themselves from their base and hang by a twisted cord of the thickened mucus 8-15 inches long. Still twisting in their embrace, they extrude from their heads their blue, club-shaped penis sacs which then extend into a fan shape at the tips. The two "penial masses" are then intertwined in a tight spiral, the upper coils expanding to form a kind of umbrella. When this is achieved, sperm transfer takes place and the slugs untwist themselves, crawl back up the mucus cord (which one of them eats), slide down the tree or wall and return to their everyday life in such damp environments as the undersides of fallen logs."

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