slugs

Slugs are a group of shell-less or nearly shell-less gastropod mollusks. The term most often refers to land slugs, which have a reduced or internal shell, but sea slugs and some freshwater species are also called slugs. Land slugs occur in moist environments worldwide, from forests to gardens.

Anatomy and physiology: Slugs belong to the class Gastropoda and typically to the clade Stylommatophora. They lack an external shell, though some retain a small internal or vestigial shell. They move with a muscular foot that glides on a mucus film, and their slime helps with moisture retention and locomotion. Most land slugs have two pairs of tentacles; the upper pair bears eyes, while the lower pair senses touch and chemical cues. Slugs are hermaphroditic, and most species mate with another individual, exchanging sperm before laying eggs in gelatinous capsules.

Ecology and behavior: Slugs are detritivores and herbivores, feeding on decaying plant matter, fungi, leaves, and fruits, with some species omnivorous or predatory on other invertebrates. They are largely nocturnal to minimize water loss. Slugs play a role as decomposers and serve as prey for birds, small mammals, and invertebrates. Reproduction is influenced by moisture and temperature, and eggs are laid in moist soil or leaf litter, with juveniles emerging after varying intervals.

Taxonomy and diversity: Slugs are not a single taxon but several families within the Stylommatophora, including Arionidae, Limacidae, Milacidae, and Agriolimacidae. Sea slugs are marine opisthobranchs, such as nudibranchs and sacoglossans, and are not closely related to land slugs. In human contexts, garden slugs are common pests in agriculture and horticulture, while slug mucus has been studied for its unique adhesive and locomotion properties.