Ariolimax columbianus




Ariolimax columbianus (Gould, 1851)

Common Name

Pacific banana slug


This robust slug can attain a length of 185 to 260 mm and may weigh up to 72 g at maturity. This species is normally yellow in color; however, several color morphs exists, that range from white to tan-green, red-brown, brown-green, olive green, slate green and ochre yellow. The mantle and body of the slug is usually of uniform color; however, the mantle in any of the color morphs may possess dark-brown to black spots, while the body remains a uniform color. In some specimens, this pattern is reversed and the body possess spots that are not present on the mantle. In some specimens, the black blotches occur simultaneously on the mantle and body and may even coalesce to give the slug a solid black. The juveniles of this species are finely speckled. This slug has a caudal mucus pore with the pneumostome (breathing pore) located behind the midpoint of the often finely granulated mantle. The keel appears undulating in strongly contracted individuals and does not reach the mantle. The sole of the foot is usually much wider than the body.

Slugs in this genus are similar in appearance; however, they can be separated based on the following genitalic characters:

A. columbianus: The penis permanently evaginated, and the apical portion is rounded/blunt. The retractor muscle is narrow and strap-shaped, and originates on the apex of the penis.

A. californicus (Cooper, 1872): The penis forms a hollow tube and can be completely invaginated. The apical portion of the penis is slender and is 1 to 1 2/3 times the length of the basal portion. The retractor muscle is broadly flabellate, and originates close to the apex of the penis.

A. dolichophallus (Mead, 1943): The penis forms a hollow tube and can be completely invaginated. The apical portion of the penis bears a flagellum that is 2 to 4 times the length of the basal portion. The retractor muscle is narrow and strap-shaped, and the point of origin is not at the apex of the penis. This species may also be aphallic (does not have a penis).

Native Range

North America


North America:

  • U.S.: Alaska, California, Idaho, Oregon, Washington
  • Canada: British Columbia


The Pacific banana slug can be found inhabiting humid coastal forests. They often are intercepted when they attempt to cross trails. This is not a pest species; however, it is commonly intercepted and may be mistakenly classified as a pest due to its large size. They are infamous for gnawing off their mating partner's penis after copulation. Oval eggs (about 5 x 8 mm) are typical of this species. The eggs are laid in clutches in the soil from autumn to early spring, maturing after three to eight weeks. The slug's diet includes fungi, feces and carrion of other slugs, and detritus and necrotic vegetation. It has been noted that A. columbianus displays homing behavior.


  • Limax columbianus Gould 1851, in Binney,Terr. Moll. U.S., 2:43, pl. 66, fig. 1; 1852, U.S. Expl. Exped. Moll., p.3, pl. 1, fig. 1.
  • Ariolimax columbianus Gould, Morch, 1859, Malak, Blatter, 6:110; W. G. Binney, 1865, Amer. Jour. Conch., 1:48, pl. 6, figs. 11-13.
  • Ariolimax columbianus var. maculatus "Cockerell", Binney, 1890, Third Suppl., Bull. M.C.Z., 19: 211, pl. 6, figs. A, G.
  • A. columbianus forma typicus and forma maculatus, Cockerell, 1891, Nautilus, 5:31; forma niger, 5:32 (All form British Columbia).
  • A. subsp. Californicus forma maculatus Cockerell, 1891, Nautilus, 5:31, foot-note; 1897, Nautilus, 11:76. (No locality given).
  • Aphallarion buttoni Pilsbry & Vanatta, 1896, Proc. Acad. Nat. Sci. Phila., p. 348, pl. 12, figs. 3, 4, 5; pl. 13, fig. 4; pl. 14, fig. 11, 12.


Burch 1962, Forsyth 2004; Mead 1943; Pilsbry 1948

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