MolluscIreland - land and freshwater
  • Arion (Arion) flagellus Collinge 1893 Durham slug
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Arion (Arion) flagellus
© Dr Roy Anderson
Arion (Arion) flagellus
© Dr Roy Anderson
Arion (Arion) flagellus
© Dr Roy Anderson

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Arion (Arion) flagellus
© Dr Roy Anderson
Arion (Arion) flagellus
© Dr Roy Anderson

A medium-large roundback slug with conspicuous dorsal tubercles and a characteristic green tint to the sole, which lives mainly on wild ground in the west and in more disturbed habitats elsewhere.

Key characteristics

  • A medium-large roundback slug varying in colour from black to russet-brown, greenish-brown or yellow-orange
  • Foot fringe lineolated but of similar colour to the back
  • Sole always pale, often tinged green; mucus pale yellow or greenish
  • Young a distinctive orange-yellow colour but with broad, dark lateral bands which run in an unbroken line across the mantle on to the back
  • Lateral bands often present, even in mature animals
  • Only 7-8 rows of tubercles between the lateral bands, against 9-10 in other large roundbacks


80-90 mm.

World Distribution

Described from near Schull in West Cork by Collinge (1893) and now widespread in the British Isles but probably introduced from Iberia before the historical period. Native in north-west Iberia (Castillejo, 1998).

GBIF distribution map [open in new tab]

Irish Distribution

In Ireland this species was very localised until the late 1980s when an expansion in both numbers and range appears to have commenced. First noticed in gardens in 1995 since when the increase in numbers has been prodigious, populations in some areas assuming plague proportions. This change in behaviour is striking and difficult to account if it were a native species. This leads naturally to speculation that Arion flagellus has more southerly origins. Quinteiro et al. (2005) sampled the genetic make-up of flagellus from British and Spanish populations and concluded that the British material did not fit the characteristics expected of a natural population and so was probably derived from the Iberian population.


  • Like most Arion this is a generalist scavenger feeding on dead vegetable and animal material, more rarely on living plants
  • Found in a great variety of habitats in the British isles, from upland acidic grassland to lowland alder carr and, now widely, in gardens


Historically confused with other large roundback slugs until definitively separated by Davies (1987).

Red List status

  • Least concern (lc).

Wikipedia link

Wikipedia page for Arion flagellus

 Anderson, R., (2016). Arion (Arion) flagellus Collinge 1893. [In] MolluscIreland. Accessed on 2024-03-03.