Long-tailed slug (Ibycus rachelae)

Also known as: ninja slug
GenusIbycus (1)
SizeLength: up to 4 cm (1)
Top facts

The long-tailed slug has yet to be classified by the IUCN.

Nicknamed the ‘ninja slug’ (2), the long-tailed slug (Ibycus rachelae) is an unusual species which was first described as recently as 2008 (1). The long-tailed slug is a type of semi-slug, being somewhat intermediate in appearance between a snail and a slug. Semi-slugs have a partially visible shell, but the shell is too small for the body to be withdrawn into (1).

Like other members of the genus Ibycus, the long-tailed slug is characterised by its particularly long tail, which in this species is three times as long as the head. As in other Ibycus species, the right lobe of the mantle is developed into a wing-like flap which covers most of the shell (1).

A fairly colourful species, the long-tailed slug has a yellowish-green body, with a yellow line running down the upper side of the tail. The head, which is usually somewhat hidden, is light to dark grey, while the shell is yellowish-brown and rounded in shape, with 1.5 whorls. The lobes of the long-tailed slug’s shell and the rear part of its body are covered in small, circular tubercles, while the tail is covered in diamond-shaped folds or ridges (1).

The long-tailed slug is known only from the state of Sabah, in Malaysian Borneo, where it is believed to occur in mountainous areas in the interior and on the west coast (1).

The long-tailed slug has been recorded living on leaves in primary montane forest, at elevations of 1,200 to 1,900 metres (1).

Relatively little is currently known about the biology of the long-tailed slug. However, this unusual species has been reported to have a habit of wrapping its long tail around its body when at rest (1).

Like many related species, the long-tailed slug has an unusual reproductive strategy which involves the use of devices known as ‘love darts’. Made of calcium carbonate, these tiny, harpoon-like structures are used to pierce and inject a hormone into a mate, and are thought to increase the chances of reproduction (2) (3) (4). Slugs and snails are hermaphrodites, with each individual possessing both male and female reproductive organs. During mating, a two-way exchange of sperm occurs between the mating pair, and both then lay fertilised eggs (5).

Although no information is available on the feeding behaviour of the long-tailed slug, like other slug and snail species it is likely to feed using a specialised organ known as the radula. The radula is covered in tiny ‘teeth’ and is used to rasp at food (5).

Little is currently known about the population status of the long-tailed slug, or about the potential threats to this species. However, native slugs and semi-slugs are reported to be generally rare and infrequently encountered in the area of Sabah in which the long-tailed slug occurs (1).

There are no specific conservation measures currently known to be in place for the long-tailed slug. However, the WWF Heart of Borneo Initiative is working with the governments of Malaysia, Brunei Darussalam and Indonesia to conserve the rainforests of Borneo through a network of protected areas and sustainably managed forests (4) (6). The importance of this has been underlined by the astonishing range of new species which are still being discovered in the Heart of Borneo forests, including the bizarre long-tailed slug (4).

Find out more about the long-tailed slug and its discovery:

More information on conservation in Borneo:

Learn more about newly discovered species on ARKive:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. Schilthuizen, M. and Liew, T.S. (2008) The slugs and semislugs of Sabah, Malaysian Borneo (Gastropoda, Pulmonata: Veronicellidae, Rathouisiidae, Ariophantidae, Limacidae, Philomycidae). Basteria, 72: 287-306. Available at:
  2. The Guardian (2010) Lungless frog and ‘ninja slug’ among new species discovered under Borneo protection plan. The Guardian, 22 April. Available at:
  3. The Guardian (2010) New species discovered in 2010. The Guardian, 25 December. Available at:
  4. Thompson, C. (2010) Borneo’s New World: Newly Discovered Species in the Heart of Borneo. WWF, Gland, Switzerland. Available at:
  5. Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Third Edition. Marshall Cavendish, New York.
  6. WWF - Heart of Borneo Forests (January, 2013)