Arion (Kobeltia) hortensis Férussac, 1819
External: Contracted body semicircular in cross-section; dark gray, bluish gray, dark brown or black body, with yellow-brown dots; dark longitudinal line with fuzzy lower edge on each side; sides paler than dorsum; black head and tentacles; fine wrinkles on dorsum; yellow to orange sole; yellow-orange body mucus (Quick 1960; Kerney & Cameron 1979; Wiktor 1983; Herbert 2010).
Internal: Dark ovotestes, yellow-white hermaphrodite duct, light pink-brown spermoviduct, yellow lower atrium with outer glandular layer; long, thin oviduct widens at base; rounded spermatheca with a short, thick duct with a widened base; spermatophore 5-6.5 mm long, variable in shape, and with a hook on its posterior end (Quick 1960).
Eggs: 2.5 x 2 mm, opaque yellow, sticky clusters to 30 eggs (Quick 1960).
Juveniles: 4-5 mm long at hatching, with darker dorsum and mantle than adults (Quick 1960); blue-black body and yellow sole (Wiktor 1983).
25-30 mm long extended (Herbert 2010).
Native in: W Europe and Scandanavia to W Russia and N Africa (Quick 1960). Synanthropic in central Europe (Wiktor 1983).
Non-native in: North America (Quick 1960).
Lampyrid beetle larvae are predators of Arion hortensis (Schwalb 1961, in Stephenson & Knutson 1966).
Synanthropic, occupying forests, gardens, parks, waste sites, and greenhouses; takes shelter under stones, dead wood, leaf litter, and in the soil (Quick 1960; Wiktor 1983).
Feed on plants, some fungus, (Chichester & Getz 1973), and roots (potato) (Chatfield 1976). Pest of carrot, potato (Quick 1960), berries, leafy crops, and flowers (Wiktor 1983).