Yellow Slug

Limacus flavus (Linnaeus 1758)
(Stylommatophora, Helicoidei, Limacacea, Limacidae)

Yellow slug (Limacus flavus) from Lower Saxony, Northern
Germany. Picture: Walter Wimmer, (NABU).

Description: The Yellow slug (Limacus flavus) is a greyish green to olive green slug, which may sometimes even have a yellowish brown colour. Its back is rounded, the tail keel is rather short. The mantle shield takes about 20% of the overall body length. Back and mantle shield of the yellow slug are show a pattern of many lightly coloured spots and blotches, which may also be orange or olive green in colour. On a yellow slug, the pattern of spots only reaches down a part of the body sides. Towards the foot rim, it is limited by a more lightly coloured zone. In that regards, the yellow slug is different from the Irish yellow slug (Limacus maculatus), a species which on the British Isles quite often shares the yellow slug's habitats. Head and tentacles of the yellow slug are grey in colour, the foot sole on the other hand is crème coloured to olive green. While the slug's body mucus is yellowish in colour, the sole mucus is colourless. Contrary to the adult slugs, the yellow slug's juveniles have a more greenish colour.

Like in many slug species, in the yellow slug as well the construction of the genital apparatus is vital in a correct determination of the species. In a yellow slug's genital apparatus, the penis is astonishingly long, it takes about one sixth of the body's overall length. The canal of the sperm pouch (spermatheca) and the oviduct join together and open in the genital atrium as a special widened structure, which is special in keel back slugs (Limacidae).

Dimensions: Length up to 150 mm.

Yellow slug (Limacus flavus) from Lancashire, England.
Picture: Chris Wallwork (Source).

Habitat and Distribution: The Yellow slug in some places also appears in high altitude mountainous habitats, but from Romania, Central and Northern Europe, as well as from Great Britain, the yellow slug is known as a commensal species, it lives mainly in habitats formed by man, such as fruit and vegetable stores, compost heaps, sewage canals, parks, but especially also in caves, on old walls, in moist cellars (sometimes it is also called the cellar slug), as well as in kitchens. In German, the yellow slug is called the beer slug ("Bierschnegel"), a name which comes from times earlier in history, when the yellow slug still could live in mouldy cellars and feed on spilt beer in breweries. In modern times of industrial beer production, hygiene stops yellow slugs from finding food there and so do the dry cellars we usually have today. In Great Britain, on the other hand, yellow slugs are quite often found in modern suburban houses. Yellow slugs exclusively are active at night.

Where the yellow slugs originally came from, is not known. Scientists assume, though, that it came from the Mediterranean. Today, the species' area of distribution spreads over almost all of Europe. It has also been introduced by man on the Canary Islands, in Chile and South Africa, on Madagascar, in North and South America, as well as in Australia and in New Zealand. In many places where the yellow slug had settled in Central Europe before, the species has disappeared today.

Although the yellow slug had not been seen in Northern Germany for 90 years, in 2005 it could be found in the beer town of Einbeck.

NABU Niedersachsen: Bierschnegel nach 90 Jahren wiederentdeckt (Yellow slug rediscovered after 90 years).

Threat Situation: In Great Britain, the yellow slug has been introduced before the 18th century. Since then it has spread vastly and today it is frequent and common in England and Wales. In Ireland and Scotland, however, its distribution is more disperse and the species is rather rare. In Central Europe the yellow slug is especially threatened by the renovation of old buildings, the drainage of cellars and by hygiene measures, especially in breweries. As a consequence, in Germany, Limacus flavus is classified as critically endangered, in Austria, the species is classified at least as vulnerable (see also: IUCN Threat Categories).

Systematic Remark: There is disagreement concerning the systematic classification and nomenclature if the yellow slug. So far, it has been listed under the systematic name Limacus flavus (Linnaeus 1758) (see also Forcart 1986), for example, the Polish malacologist and slug specialist Andrzej Wiktor, disagrees - in his opinion, the genus Limacus ought to have the status of a subgenus, as a part of the Genus Limax.

Mollbase: Limacus flavus.
Francisco Welter-Schultes: Limax flavus species homepage.
Terrestrial Mollusc Tool: Limacus flavus.
Herbert, D.; Kilburn, D. (2004): A field guide to the land snails and slugs of eastern South Africa; p. 296.