Invertebrates Active at night

Black Slug

Arion ater

iNaturalist Wikipedia

The undisputed titan of the garden floor, the Black Slug is a master of moisture and a crucial, if misunderstood, member of the decomposition squad. Known for its massive size and glossy, jet-black appearance, this nocturnal gastropod is a fascinating subject for any backyard observer.

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0 Habitats

Quick Identification

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Size

10-15 cm (4-6 inches) in length, though can reach up to 20 cm (8 inches) when fully extended while crawling.

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Colors

Usually jet black, but can appear in shades of brown, orange, or greenish-grey; the foot fringe often features subtle orange or yellow transverse stripes.

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Key Features

Large, bulky body without an external shell
Round back when resting, lacking a dorsal keel
Contracted 'hunch' or bell-shaped posture when threatened
Coarse, wrinkled skin texture
Respiratory pore (pneumostome) located on the right side of the mantle.

When You’ll See Them

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Activity pattern Active at night

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Peak hours 9 PM - 4 AM

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Season April-October (during wet weather)

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Diet A generalist scavenger and herbivore that eats rotting vegetation, fungi, carrion, and animal feces, as well as fresh garden plants.

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Habitat Damp environments including suburban gardens, deciduous woodlands, hedgerows, and moist grasslands.

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Where Does the Black Slug Live?

Native to the cool and temperate regions of Western and Northern Europe, the Black Slug is a ubiquitous sight from the British Isles and Scandinavia down through Germany and France. Due to its hardy nature, it has been introduced to various parts of the world, most notably establishing significant populations in North America, particularly along the Pacific Northwest coast and Atlantic Canada. It thrives in maritime climates where humidity is high and winters are relatively mild, often becoming the dominant slug species in these introduced territories.

Basemap © OpenStreetMap contributors

9 Countries

12.5M km² Range

Least Concern Conservation

GB United Kingdom Ireland DE Germany FR France NO Norway SE Sweden CA Canada US United States Iceland

Elevation range

0 m1,000 m2,000 m4,000 m

Sea level – 2,000 m

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iNaturalist / Verified observation data

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Behavior

The Black Slug is a primarily nocturnal creature, highly dependent on moisture to prevent its soft body from drying out. During the day, it typically seeks refuge under logs, stones, or deep within garden litter. One of its most distinctive behaviors occurs when it feels threatened: instead of retreating into a shell, it contracts its body into a tough, hemispherical ball and often rhythmically sways from side to side to deter predators.

As hermaphrodites, these slugs possess both male and female reproductive organs, though they usually seek a mate for cross-fertilization. Their movement is powered by a muscular 'foot' that secretes a layer of thick mucus, which not only facilitates gliding but also serves as a chemical trail for other slugs to follow. In garden settings, they are often solitary foragers but may congregate in high numbers around particularly rich food sources like compost heaps.

photo_camera EverydayEarth exclusive

Camera Tips

Capturing a Black Slug on camera requires a shift in strategy compared to filming birds or mammals. Because slugs are cold-blooded and move slowly, traditional PIR (Passive Infrared) motion sensors on trail cameras often fail to trigger. To successfully document them, use 'Time-Lapse Mode' set to intervals of 30 seconds to 1 minute. This ensures you catch their slow progression across the frame and creates a fascinating video effect as they glide and extend their tentacles.

Placement is everything—your camera must be at ground level. Prop your camera up with a small block or use a low-profile stake to aim the lens slightly downward towards a damp, flat surface. For the best results, use a camera with a close-focus or macro lens capability, as standard trail cams may have a minimum focus distance of 3 to 5 feet, which is too far for such a small subject. Aim for a focus distance of 12-18 inches if possible.

To guarantee a visit, you can use a harmless attractant. A shallow dish of beer (a 'beer trap' setup) or a few slices of overripe melon or cucumber will bring them into the frame within hours of nightfall. If your camera has adjustable LEDs, use the 'Low Glow' or 'No Glow' setting to prevent overexposing the slug's glossy, reflective skin, which can easily turn into a white blob in night shots. Positioning the camera near a known 'slime trail' on a garden path is a surefire way to catch them in transit.

Similar Species

Species that look similar or are commonly confused with Black Slug.

Leopard Slug

Features a distinctive spotted pattern and a 'keeled' back, unlike the solid-colored, round-backed Black Slug.

Spanish Slug

Often reddish-brown and nearly impossible to distinguish visually from Arion ater without dissection, but typically more aggressive in its garden consumption.

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Frequently Asked Questions

Black Slugs are almost exclusively nocturnal. They emerge shortly after dusk when humidity levels rise and the sun's drying heat has faded. On particularly rainy or overcast days, you may occasionally see them active during the afternoon.

You can attract them by creating 'slug hotels'—flat boards or damp cardboard laid on the soil. They are also highly attracted to fermenting scents, so a shallow dish of beer or compostable fruit scraps will quickly bring them out of hiding for your camera.

They are omnivorous scavengers. While they are famous for eating garden plants like lettuce and marigolds, they also perform a vital service by eating decaying leaves, fungi, animal droppings, and even dead worms or other slugs.

Yes, they are highly adapted to suburban life. The abundance of watered gardens, compost heaps, and artificial shelters like flower pots makes suburban backyards an ideal habitat for them to thrive.

It is quite easy! The Black Slug is usually solid black or orange and has a rounded back. The Leopard Slug (Limax maximus) is usually pale grey or tan with distinct black spots or stripes and has a raised ridge or 'keel' near its tail.

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