Black Slug

Black Slug — Arion ater

The Black Slug (Arion ater) is one of our largest and most familiar land molluscs, growing up to 15 cm long, with a smooth, glossy body ranging from jet‑black through dark grey to reddish‑brown or even pale cream. It is a hermaphrodite, each individual possessing both male and female reproductive organs, and lays small, round, pearly white eggs in damp crevices beneath logs or soil. Active mainly at night and during damp weather, it feeds on a wide variety of plant matter — living and decaying — as well as fungi and occasionally carrion, playing an important role in breaking down organic material and recycling nutrients. Contrary to its lowland reputation, it is remarkably hardy and adaptable: while most abundant in gardens and woodlands, it is recorded well into the uplands, with confirmed sightings above 900 metres on Scottish mountains including Schiehallion. It survives exposed conditions by retreating into crevices or under vegetation during dry spells, and produces a thick protective mucus layer that helps it resist desiccation and temperature extremes — impressive resilience for a soft‑bodied creature found so close to a mountain summit.