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Montana Field Guides

Hedgehog Arion - Arion intermedius
Other Names:  Limax intermedius

Non-native Species

Global Rank: G5
State Rank: SNA

Agency Status

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General Description
A small slug, reaching 15-25 mm extended. Dorsal base color usually pale yellowish-gray, the head and tentacles darker, the mantle more yellow in the anterior half. The mantle is about 1/3 the body length, and covered with a series of small tubercles that form sharp translucent points when the animal is contracted; lateral bands are very pale or absent. The pneumostome is in the anterior half of the mantle on the right side, posterior to the mantle cleft. There is no mid-dorsal keel on the tail, lateral bands on the tail are pale or absent. The sole is pale yellow to pale orange; the mucous is yellowish to orangish-yellow. Because of small adult size, it can be confused with juveniles of other Arion species (McDonnell et al. 2009, Hendricks 2012, Burke 2013). Internal anatomy is described by Pilsbry (1948) and Cadiz and Gallardo (2007).

Diagnostic Characteristics
Arion lack an elevated visceral hump, possess a mantle about 1/3 the length of the animal with the pneumostome in the anterior half of the mantle, have an undivided foot, lack a dorsal keel on the tail, have a relatively broad tail covered with rows of prominent turbercles and with a caudal mucous pit at the tip where the pedal furrows meet. A. intermedius differs from other members of the genus by a combination of it's small size (usually less than 20 mm), pale gray to pale yellowish color, indistinct bands on sides, lack of mantle speckles, dark head and tentacles, pale yellow sole, and production of lemon-yellow mucous; when contracted, points form on the turbercles.

Species Range
Montana Range


Range Comments
Native to central and northern Europe; introduced in Polynesia, Australia and New Zealand, northern Africa, and the Americas (Forsyth 2004, Burke 2013). In Montana, reported west of the Continental Divide in Lincoln and Sanders counties from two U. S. Forest Service campgrounds. Elevation range is 672 to 1067 m (2205 to 3500 ft). Not reported in Montana prior to 2006, but with additional surveys in appropriate areas of human activity it probably will prove to be more widespread. May be locally abundant; 36 individuals reported at the Sanders County site and 39 at the Lincoln County site, both in early October (Hendricks 2012).

Observations in Montana Natural Heritage Program Database
Number of Observations: 2

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Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Occupies moist areas within forested or shrubby locations, such as stream-sides and marshy areas and lake shore near areas of human activity, such as campgrounds and other disturbed sites, also gardens and parks in residential areas. Forest canopy in Montana includes western redcedar, Engelmann spruce, and western larch, with a secondary canopy of alder. Most often found under woody debris and leaf litter (Hendricks 2012).

  • Literature Cited AboveLegend:   View Online Publication
    • Burke, T. E. 2013. Land snails and slugs of the Pacific Northwest. Corvallis, OR: Oregon State University Press. 344 p.
    • Cadiz, F.J. and C.S. Gallardo. 2007. Arion intermedius (Gastropoda: Stylommatophora); first record of this introduced slug in Chile, with notes on its anatomy and natural history. Revista Chilean de Historia Natural 80:99-108.
    • Forsyth, R.G. 2004. Land snails of British Columbia. Royal British Columbia Museum: Victoria, British Columbia, Canada. 188 pp.
    • Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.
    • McDonnell, R. J., T. D. Paine, and M. J. Gormally. 2009. Slugs, a guide to the invasive and native fauna of California. University of California Division of Agriculture and Natural Resources Publication 8336. 21 p.
    • Pilsbry, H.A. 1948. Land Mollusca of North America (north of Mexico), Volume II Part 2. The Academy of Natural Sciences of Philadelphia Monograph Number 2(2): 521-1113.
  • Additional ReferencesLegend:   View Online Publication
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    • Frest, T.J. and E.J. Johannes. 2001. An annotated checklist of Idaho land and freshwater mollusks. Journal of the Idaho Academy of Science 36(2):1-51.
    • Grimm, F.W., R.G. Forsyth, F.W. Schueler, and A. Karstad. 2009. Identifying land snails and slugs in Canada: introduced species and native genera. Canadian Food Inspection Agency, Ottawa, ON. 168 pp.
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Citation for data on this website:
Hedgehog Arion — Arion intermedius.  Montana Field Guide.  .  Retrieved on , from