Black slug
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| Arion ater (Linnaeus, 1758) |
The black slug (sometimes black arion, European black slug, large black slug, or the Northern menace) is a terrestrial slug species found in northern Europe (including Britain) and the Pacific Northwest.[1]
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[edit] Characteristics
The size of the slug varies from 10-15 cm (4-6 inches) among fully extended adults. Maturity is reached at about 2½ cm (1 inch). [2]
The colour of the black slug is generally black, but varies greatly and can even be white. The general trend is for a darker pigmentation the farther north the species is found. The classification of brown-coloured black slugs is somewhat disputed; the brown variation is sometimes considered to be a separate species, Arion rufus (Red Slug).[2] Young specimens of black slug do have a brown color, which is later lost when (if) the slug changes color to the mature state.[1]
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. If a person comes in contact with it, the mucus can be difficult to wash off.[3]
Like other members of the Arionidae family, the black slug has a pneumostome (breathing hole) on its mantle through which it breathes. This mantle is the part which most closely qualifies as a shell, having a resilient protective structure embedded within it.[1]
[edit] Behaviour
The black slug is mainly nocturnal and avoids exposure to sunlight. It is omnivorous,[4] eating carrion, fungi, and vegetation (living and decaying). The slug prefers moist conditions, such as lawns, making it an unwelcome sight for homeowners.[1] This moist environment is essential for the terrestrial locomotion of the slug to function.
Like all other species of the Arionidae family, the black slug is a hermaphrodite, meaning it can fertilize itself if needed, although a mate is preferred. After mating, the slug lays eggs about 5 mm in diameter. The favoured location for eggs are a dark, cold, damp place such as a compost heap.
In the past two decades, its mating with the non-native (at northern latitudes) pest species Arion lusitanicus (or Spanish slug) has resulted in a more resilient hybrid exhibiting increased tolerance to cold.[5]
The mucus of the slug is highly distasteful to most animals. However, it does have a few natural predators, including the hedgehog, badger, shrew, mole, mouse, frog, toad, snake, carnivorous beetle, and some birds.[6] When picked up or touched, the black slug will contract to a hemispherical shape and begin to rock from side to side. This defensive behaviour confuses predators, and is unique in the Arionidae family.[7]
[edit] Control
The are several means of controlling the spreading of the species in gardens, the most common practices involve gathering individuals and boiling them or drenching them in salt water, which is fatal to slugs. There are also commercially available poisons, as well as traps.
Control of slugs is generally done in the spring, as each surviving slug could result in about a hundred new slugs. The amount of slugs can also be greatly reduced by not keeping a compost heap too near the garden.
[edit] References
- ^ a b c d Arion ater on Animal diversity web
- ^ a b Arion ater at University of Paisley
- ^ The world of snails
- ^ Svart skogssnigel - Arion ater at Natural history museum of Gothenburg
- ^ symposium at Canterbury Christ Church University College, Kent, UK, on 8-9 September 2003 from Malacological Society of London
- ^ Nickel, June 1998. The Slimy, Yet Special Slug. Natural History, 107:18.
- ^ The large black slug
