Chocolate arion vs Dusky arion

Arion rufus compared with Arion subfuscus

Key Differences

• Chocolate arion is Vulnerable while Dusky arion is Data Deficient.

Taxonomic Classification

Rank	Chocolate arion	Dusky arion
Kingdom same	Animalia (Animals)	Animalia (Animals)
Phylum same	Mollusca (Mollusks)	Mollusca (Mollusks)
Class same	Gastropoda (Gastropoda)	Gastropoda (Gastropoda)
Order same	Stylommatophora (Stylommatophora)	Stylommatophora (Stylommatophora)
Family same	Arionidae	Arionidae
Genus same	Arion	Arion
Species	Arion rufus	Arion subfuscus

Evolutionary Relationship

Chocolate arion and Dusky arion share a common ancestor at the Genus level: Arion.

Conservation Status

Chocolate arion

VU — Vulnerable

Dusky arion

DD — Data Deficient

Physical Characteristics

Attribute	Chocolate arion	Dusky arion
Diet	—	—
Average Lifespan	—	—
Average Length	—	—
Average Weight	—	—

Habitat & Geographic Range

Chocolate arion

Habitat

Inhabits temperate broadleaf and mixed forests and Mediterranean forests and woodlands within the Palearctic biogeographic realm. Populations are also found in montane and highland environments at higher elevations.

Range

Found across Europe (7 countries) and North America (United States). Currently classified as Vulnerable on the IUCN Red List, this species faces significant conservation challenges across its range.

Dusky arion

Habitat

Typically found in terrestrial and aquatic habitats including forests and freshwater.

Range

Found across Europe (5 countries) and North America (United States).

Chocolate arion

The Chocolate Arion (Arion rufus), also known as the Large Red Slug or Chocolate Slug, is one of Europe's largest terrestrial slugs, with adults reaching up to 15 centimetres in length. It belongs to the family Arionidae within the phylum Mollusca, and despite its common name, adults display highly variable colouration ranging from reddish-orange to dark brown and nearly black — only certain colour morphs exhibit the chocolate-brown hue that partly inspired the name. Arion rufus is native to western and central Europe, where it inhabits woodland, hedgerows, gardens, agricultural land, and other moist habitats. It is also established as an introduced species in parts of North America. Like other arionid slugs, it is primarily a detritivore and herbivore, consuming dead plant material, fungi, living plant tissue, and sometimes carrion. It shelters under logs, stones, and leaf litter during dry or cold conditions, becoming active — particularly at night — during warm, moist weather. Chocolate arion can cause significant damage to gardens and crops. Reproduction is hermaphroditic; slugs exchange sperm and lay batches of translucent eggs in soil or under debris. The IUCN classifies this species as Vulnerable, reflecting pressures on native European populations from habitat change and, possibly, competition and hybridisation with related Arion species.

Shared Countries

Both species can be found in 5 countries:

🇧🇪 Belgium 🇫🇷 France 🇳🇴 Norway 🇸🇪 Sweden 🇺🇸 United States