This species has a very unusual and distinctive mating method, where the pair of slugs use a thick thread of mucus to hang suspended in the air from a tree branch or other structure.

[6] The greater part of the body is rounded, but there is a short keel on its tail, with about 48 longitudinal rows of elongate, detached tubercles.

The shield is rounded in front, angular behind, and forming an angle of about 80 degrees when in motion, usually of a similar tint to the body, but boldly marbled or maculate with black, somewhat concentrically and interruptedly ridged around a sub-posterior nucleus.

The shape of the shell is oblong-oval and thin, slightly convex above, and correspondingly concave beneath, with a membranous margin.

The apex or nucleus is at the posterior margin but inclined towards the left side, and forming the apophysis by which the shell is organically attached to the animal.

The pedal ganglia are placed beneath the radula sac and joined by an anterior and a posterior commissure.

The spermoviduct is thick and well convoluted, and separates further down into a vas deferens or sperm-duct (VD) and an oviduct (OV).

The former opens into the upper end of a very long penis (P), to which a strong retractor muscle (PRM) is attached.

This species is now widely distributed around the world, but it is generally considered to be native to Europe and Mediterranean countries of Africa.

[11] The homing instinct is strongly developed in this species, which, after its nocturnal rambles or foraging expeditions, usually returns to the particular crevice or chink in which it has established itself.

[16][17] It can also detect deficiencies in a nutritionally incomplete diet if the essential amino acid methionine is experimentally removed from its food.

It does however exhibit a decided preference for the vicinity of human habitations, and readily takes up its abode in damp cellars or outbuildings.

[7] In Ireland, this predilection for human dwellings is not exhibited, and the species is restricted to woods and other similar places.

It is a detrivore, cleaning up dead plants and fungi,[7] and a carnivore known to pursue other slugs at a top speed of 15 centimetres (6 in) per minute.

Parasites of Limax maximus include the nematode Agfa flexilis, which lives in its salivary glands,[7][unreliable source?]

[11] A meningitis-causing nematode, Angiostrongylus cantonensis, which normally infests the lungs of rats, has a larval stage which can only live in molluscs, including slugs.