Where’s Wildlife · Snail & Slug Field Guide
Arion sp.
Pronounced (approx.): AIR-ee-on
Orange Arion slugs photographed at Edward L. Ryerson Conservation Area, Illinois; possibly the Dusky Arion group (A. subfuscus/fuscus).
Arion sp., possibly the Dusky Arion group. Select a photograph to compare views. © Where’s Wildlife.
ARION · SPECIES UNRESOLVED
Slug lengths refer to extended animals; snail measurements refer to the shell.
Mantle forms a saddle over the front portion
Rounded tail with an apparent mucus pore at its tip
Orange body; color alone does not establish the species
Compare views, markings and body shapes in the photographs below.
Working identification: Arion sp., possibly the Dusky Arion group (A. subfuscus/fuscus). The rounded tail and apparent caudal mucus pore support Arion. Species-level identification remains provisional.
These photographs were previously labeled Gray Fieldslug (Deroceras reticulatum). They are now treated as Arion sp. Similar Arion species can be difficult to separate; the suggested Dusky Arion group is not a confirmed species identification.
Woodland logs and damp ground at Ryerson Woods, Illinois. Adults feed on plants, fungi and other organic material. Mostly at night or in cool, damp weather.
The photographer observed thousands of similar slugs after rain at Ryerson Woods. Damp conditions allow slugs to emerge from shelter, move and feed. Abundance after rainfall does not identify the species.
Thousands of similar slugs were observed at this location after rain.
Tail structure helps distinguish slug groups.
Slugs are gastropod mollusks, related to snails.
These photographs document the Ryerson Woods observation in northeastern Illinois. A separate published photograph also records Arion at Ryerson Woods. The precise species and its full range remain unresolved.
Explore reported sightings on iNaturalist. Observation records are not a complete range map.
Photographs © Where’s Wildlife.