MolluscIreland - land and freshwater
  • Geomalacus (Geomalacus) maculosus Allman 1843 Kerry slug
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Geomalacus (Geomalacus) maculosus
© Dr Roy Anderson
Geomalacus (Geomalacus) maculosus
© Dr Roy Anderson
Geomalacus (Geomalacus) maculosus
© Dr Roy Anderson

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Geomalacus (Geomalacus) maculosus
© Dr Roy Anderson

A large and handsome slug, in its typical form black in colour ornamented with white or blue-white spots. Can curl into a ball like a pillbug woodlouse. Confined to south-west Ireland and north-west Iberia but common only in Ireland.

Key characteristics

  • Medium large roundback slug with two colour forms: black with whitish spots; or brown with lateral bands and marbled with yellowish spots
  • Can roll into a ball like a pillbug woodlouse when handled
  • Mucus colourless
  • Sole white
  • Eggs oval rather than round as in Arion


60-90 mm.

World Distribution

Restricted to south-west Ireland and north-west Iberia. Distribution type: Suboceanic Southern-temperate (82).

GBIF distribution map [open in new tab]

Irish Distribution

Its distribution and status in Ireland is summarised by Platts & Speight (1988). It is common in parts of West Cork, South Kerry and North Kerry, in areas where acidic Devonian sandstone rocks outcrop. Its presence there is an old biogeographical puzzle but, along with other so-called Lusitanian elements of the Irish fauna and flora, it is possible that it was accidentally introduced at an early date by man. In the Stone and early Bronze Ages commerce between Iberia and south-west Ireland was well-developed and could have provided the mechanism for transfer.


  • Feeds mainly on lichens and algae on outcropping rocks
  • Usually found under large stones in open Atlantic heath but also on stone dykes along road margins
  • It also seems well adapted to life in broadleaf woods where it may be abundant sheltering in crevices on the trunk or under mosses on limbs
  • Its range corresponds roughly to frost-free areas in south-west Ireland

Red List status

  • Protected in Ireland and listed in Annexes II and IV of the Habitats Directive
  • Least Concern (lc) in a recent Irish Red Listing exercise (Byrne et al., 2009)

Wikipedia link

Wikipedia page for Geomalacus maculosus

 Anderson, R., (2016). Geomalacus (Geomalacus) maculosus Allman 1843. [In] MolluscIreland. Accessed on 2024-05-22.