MolluscIreland - land and freshwater
  • Semilimax pyrenaicus (A. Férussac 1821) Pyrenean glass snail
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Semilimax pyrenaicus
© Dr Roy Anderson
Semilimax pyrenaicus
© Dr Roy Anderson

Map hosted by the National Biodiversity Data Centre, Waterford
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A 'semi-slug' with very flat and depressed shell and body clearly too big to be contained within it. Shell with a very large body whorl, and very thin, transparent and glossy with a faint greenish or yellowish tint. The animal is usually pale grey with darker spots but may be nearly uniformly dark grey or blackish. Very local but apparently increasing.

Key characteristics

  • A semi-slug with very flat and depressed shell in which the body whorl is ¾ of the total breadth viewed from above
  • Shell very thin, fragile, transparent and with a greenish or yellowish tint
  • Aperture with a mouth membrane running from the umbilicus along the inside of the outer lip
  • Animal pale to dark grey or black, paler forms having large darker grey blotches


5-6 mm.

World Distribution

Recorded only from Ireland, north-west France including Brittany (pers. comm. of B. Yannick) and the Basses Pyrénées in western France. Distribution type: Oceanic Temperate (71).

GBIF distribution map [open in new tab]

Irish Distribution

In the last century this lively and rather brightly coloured animal was known only from disturbed sites on the borders of Louth and Meath. It has since been found widely across Ireland (Kerney, 1999). Sites include Glenariff Co. Antrim (Anderson, 1974), the Lower Bann woodlands near Coleraine and the north-east corner of Lough Neagh, Co. Antrim (Anderson, 1977), Knockmany Forest Co. Tyrone (Anderson, 1978), several sites in and around Belfast (Anderson, 1991, 1992a), Humewood Castle, Co. Wicklow (Kerney, 1978a), Cappoquin, Co. Waterford and Torc Cascade, Killarney, North Kerry (Fogan, 1969). It is seemingly spreading via forestry operations in the north-east (Anderson, 1992a) and perhaps elsewhere.


  • Known sites for this species are all enclosed and lack grazing disturbance - it may be increasing because stock are now mostly excluded from woodlands in Ireland
  • It is usually abundant under fungoid logs and branches but also in leaf and grass litter
  • More rarely it has been found in pure conifer stands and it adapts well to conifer-broadleaf mixtures
  • Abundant where it occurs in wet woods such as floodplain alder or willow carr

Red List status

  • Least concern (lc).

Wikipedia link

Wikipedia page for Semilimax pyrenaicus

 Anderson, R., (2016). Semilimax pyrenaicus (A. Férussac 1821). [In] MolluscIreland. Accessed on 2024-03-02.