MolluscIreland - land and freshwater
  • Arion (Kobeltia) occultus Anderson 2004 Disappearing slug
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Arion (Kobeltia) occultus
© Dr Roy Anderson
Arion (Kobeltia) occultus
© Dr Roy Anderson
Arion (Kobeltia) occultus
© Dr Roy Anderson

Map hosted by the National Biodiversity Data Centre, Waterford
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Arion (Kobeltia) occultus
© Dr Roy Anderson
Arion (Kobeltia) occultus
© Dr Roy Anderson

A member of the garden slug group and difficult to distinguish from Arion distinctus but slightly larger and broader and with coarser dorsal tubercles, which appear ridged when at rest. Mainly yellow-grey in colour due to numerous yellow chromatophores on the back. Sides paler than in Arion distinctus.

Key characteristics

  • A garden slug with elongate depressed body similar to Arion distinctus but able to asssume a half moon shape at rest
  • Colour yellowish-grey with broad lateral bands and pale sides; sole a watery yellow
  • Tubercles coarser than those of Arion distinctus but this is not obvious except when fully contracted
  • Tentacles dark grey
  • Mucus yellow, especially on the back


35-42 mm.

World Distribution

Presently unknown outside Ireland.

GBIF distribution map [open in new tab]

Irish Distribution

Almost certainly an introduction of relatively recent date but the country of origin is unknown. Discovered in May 1986 in a former rubbish dump, now planted with sycamore and spruce, on the Dunleath Estate at Ballywalter Bay, Co. Down (Anderson, 2004). Specimens have recently (2009) been discovered in a garden centre in Donaghadee about ten miles to the north and suggest that some spread is taking place. A report of its occurrence on Inishmore Island, Galway Bay (Beckmann, 2007) requires confirmation.


  • Burrows shallowly in soil into which it can disappear for prolonged periods during dry or cold weather
  • Lives in sandy soil under planted sycamore and spruce at Ballywalter
  • Also found under decaying seaweed on open ground near the shore

Red List status

  • Not applicable.

Wikipedia link

Wikipedia page for Arion occultus

 Anderson, R., (2016). Arion (Kobeltia) occultus Anderson 2004. [In] MolluscIreland. Accessed on 2024-03-02.