Arion (Mesarion) subfuscus (Draparnaud, 1805)
A. subfuscus are relatively aggressive to other slugs (Rollo & Wellington 1979).
Arion sibiricus, A. lusitanicus, juvenile A. ater.
External: Body variably-colored, ranging from yellow-brown, orange, olive, to red-brown; darker stripe on each side of body and mantle; darker dorsum and head; relatively fine skin tubercles; yellowish foot fringe marked with darker lines; creamy sole with tiny whitish spots; body mucus orange to yellow, and sole mucus colorless, and releases orange mucus if irritated; most of yellow/orange body color is due to the mucus; limited ability to contract into a hemisphere (Quick 1960; Kerney & Cameron 1979; Wiktor et al. 2000).
Internal: Light brown ovotestis, pink-gray common duct; long vas deferens; junction of epiphallus and atrium is surrounded by a ring; oviduct contains two strong longitudinal folds; spherical spermatheca, with spermatheca duct 2x its length and wide at its origin; short, rounded atrium with glandular layer around lower atrium; 20 mm long spermatophore with fine tail, fine serration on convex edge (Quick 1960; Wiktor et al. 2000).
Similar to A. lusitanicus and juvenile A. ater, but can be distinguished by having finer skin tubercles, orange body mucus, and can't contract fully into a hemisphere (Kerney & Cameron 1979). Very similar to A. sibiricus but has a lighter body and thinner genitalia (Wiktor et al. 2000).
Eggs: 2.25 x 2.25-3.25 mm, opaque, white becoming yellow to brownish with age, adhering to the rest of the cluster. Clutch up to 50 eggs (Quick 1960).
Juveniles: 6 mm long and gray at hatching (Quick 1960).
50-70 mm long extended (Kerney & Cameron 1979); preserved to 40 mm long, 11 mm wide, 12 mm long mantle (Wiktor et al. 2000).
Native to: all of Europe excluding S-most parts, E through Ural Mts. and some (possibly introduced) in China (Wiktor et al. 2000).
Nonnative to: USA and S Canada (Chichester & Getz 1969).
Predators include lampyrid beetle larvae (Schwalb 1961, in Stephenson & Knutson 1966) and red-backed salamander (Plethodon cinereus) (Maerz et al. 2005).
Usually forest-dwelling and sometimes cultivated habitat (Chichester & Getz 1969); both deciduous and coniferous forest, gardens, hedges, wasteland (Quick 1960; Kerney & Cameron 1979; Kappes 2008); often occurs in mountains, up to subalpine areas with lichen-covered rocks to 2900 m (Wiktor 1983). Takes shelter in moist, shady habitat under logs and leaf litter (Quick 1960).
Although most invasive slugs occupy disturbed habitat, A. subfuscus has penetrated deeply into undisturbed forests in North America (Chichester & Getz 1969).
Lives 13-17 months (Wiktor 1983).
Feeds on diverse foods in the field including fungus (in particular), senescent and dead plants, algae, feces, and dead animals. In the lab, feeds on lettuce, carrots, grain, and dead slugs (Quick 1960; Beyer & Saari 1978).