Description
The size of the slug varies from 10 to 15 cm. Maturity is reached at about 2.5 cm.
The color of the black slug is generally black, but the colouration is very variable and this slug can even be white. The general trend is for a darker pigmentation the farther north the species is found. The classification of brown-coloured and rust-coloured "black" slugs is somewhat disputed; the brown variation is sometimes considered to be a separate species, Arion rufus (Red Slug). Young specimens of black slug do have a brown colour, which is later lost if and when the slug changes color to the mature state.
The slug covers itself in a thick foul-tasting mucus which serves as both protection against predators as well as a measure to keep moist. It is somewhat difficult to wash off.
Like other members of the family Arionidae, the black slug has a pneumostome (breathing hole) on the right side of its mantle through which it breathes. This mantle is the part which in snails secretes a shell, and in this species of slug the mantle contains a resilient protective structure of calcareous granules.
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White variant of the black slug
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Brown variant of Arion ater
Read more about this topic: Black Slug
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