Species of the week: Black Slug

Oct 09

Black Slug, also known as Black Arion

Arion ater
Seilide Dubh

The black slug, also known as black arion, is a species of large land slug, a terrestrial slug in the family Arionidae, the roundback slugs. 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 deep black, but the colouration is variable and this slug can even be white. Juveniles are ivory whitish with black head, but soon become greyish, half-grown animals are often black like adults. The foot-fringe is black. The tubercles large and elongate. The sole is blackish grey.

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 secrete a shell, and in this species of slug the mantle contains a resilient protective structure of calcareous granules

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 20-50 eggs about 5 mm in diameter. The favoured location for eggs is a dark, cold, damp place such as a compost heap. The eggs typically hatch in six weeks.

The slug covers itself in a thick foul-tasting mucus which serves as protection against predators and as a measure to keep moist. It is somewhat difficult to wash off. The mucus is highly distasteful to many animals. However, this slug does have some natural predators, including the hedgehog, badger, shrew, mouse, frog, toad, carnivorous beetle, and some birds. 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.

The black slug is mainly nocturnal and avoids exposure to sunlight. It is omnivorous, eating carrion, fungi, and vegetation (living and decaying). The slug prefers moist conditions, such as lawns. This moist environment is essential for the terrestrial locomotion of the slug to function.

Photo: Prashanthns, Wikipedia