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dusky arion

dusky arion (Arion subfuscus) [nonnative]
Photo © Marla Coppolino

Features and Behaviors

This slug may reach a maximum length of about three inches. Slugs have a complex system of organs. The mouth contains a radula, a flexible, ribbonlike structure lined with rows of teeth, used to scrape food. On the head are tentacles. Most slugs in Illinois have an eye at the tip of each upper tentacle. Slugs have either a much-reduced shell, located under the mantle on the dorsal side, or no shell.

Slugs need to seek sheltered places to live, eat and rest. They prefer to live in moist areas and are commonly found under logs, loose bark or coarse woody debris, and in leaf litter on the forest floor. Most slugs are hermaphrodites, possessing both male and female sex organs and gametes. When slugs mate, fertilization often occurs in both individuals, and both lay a clutch of eggs. Slugs lay their eggs in spring and fall. Eggs are deposited in a cool, damp place, often just under the soil’s surface. The adult slug provides no care for the eggs. Hatching takes place in about seven to 10 days. The young slugs emerge and begin to search for food immediately. A slug’s skin contains glands that produce mucus. The mucus prevents the slug from drying out and also helps it move. During very hot, dry weather and during very cold periods, slugs may become inactive. Slugs eat live and decaying vegetation. This slug is introduced from Europe. It generally lives around human habitations and can be a garden pest.

Illinois Range


​Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Order: Stylommatophora
Family: Arionidae

Illinois Status: common, nonnative