Red triangle slug fact sheet

What is a red triangle slug?

Red triangle slugs are Australia’s largest native land slug, reaching sizes up to 14 centimetres in length.

They are named after the distinctive red triangle on their back which contains their breathing pore, called a pneumostome. The scientific name for red triangle slugs is Triboniophorus graeffei.

Red triangle slugs belong to a group of molluscs called  gastropods  -  gastro  meaning stomach and  pod  meaning foot. This group includes all snails and slugs.

Red triangle slugs have a distinctive red triangle, breathing pore and two tentacles.

What do red triangle slugs look like?

Red triangle slugs are a type of leaf-vein slug, meaning they have a vein running down their back which resembles the vein of a leaf.

Many native slugs have only one pair of tentacles on their head, whilst some introduced slug species have 2 pairs.

Red triangle slugs can be a variety of colours including white, off-white, yellow, grey, beige, pink, red and olive green, although all varieties share the same distinctive red triangle. Scientists are currently trying to determine whether these colour variations are in fact different species of red triangle slugs.

External features of a red triangle slug include its red triangle with breathing hole and two tentacles on its head

A pale pink colour variant of the red triangle slug

Where do red triangle slugs live?

Red triangle slugs are found along the east coast of Australia. The natural habitat of red triangle slugs include forests, woodlands and heath where they can be found living in moist areas such as under bark, rocks and logs. During wet weather they can be found crawling on top of rocks, along tree trunks and branches.

Red triangle slugs are also commonly found in urban areas and are frequently sighted in gardens and sometimes bathrooms.

Red triangle slugs live in forests such as this one in the Field of Mars Reserve.

What do red triangle slugs eat?

Red triangle slugs bury themselves in leaf litter during the day and at night come out to feed. They graze on moss and microscopic algae which grow on the surfaces of smooth-barked gum trees and rocks. As they graze they leave behind scalloped tracks – small arc-shaped markings like chain links.

If a red triangle slug makes its way into a house it has also been known to graze on bathroom algae – a natural bathroom cleaner.

Scallop-shaped feeding trail of a red triangle slug found on a smooth barked tree in the Field of Mars Reserve.

What eats red triangle slugs?

Common predators of red triangle slugs include frogs, reptiles, bats and birds.

How are red triangle slugs adapted to their environment?

Red triangle slugs have an unusual defensive mechanism – they secrete a sticky mucus from their backs strong enough to superglue predators down to surfaces, allowing the slug to get away, albeit a slow get away. The stickiness of the mucus is so strong that it can leave predators pinned to a surface for days. Scientists are still trying to determine how red triangle slugs don’t get stuck to it themselves when using this defence mechanism.

Red triangle slugs secrete slime for movement and defence.

How do red triangle slugs reproduce and what is their life cycle?

Slugs are hermaphrodites meaning they have both female and male reproductive parts. This makes it easy for slugs to find a mate.

Red triangle slugs lay eggs in damp areas of the forest floor. They are often laid under leaf litter or under a fallen log for protection.

Juveniles – young slugs – have a slightly different appearance to adults lacking both the distinctive red triangle and red border around their body. Instead, juveniles have a triangle outlined in grey and three dark grey stripes running down their backs.

Red triangle slugs may live up to 3 years.

Red triangle slugs encircle each other when mating.

Related fact sheets

More invertebrate and environment fact sheets

• Invertebrate fact sheets – overview
• Gastropods fact sheet – background on the snail and slug group.
• Millipedes fact sheet – other leaf-litter decomposers living under logs and in moist habitats.
• Pill bugs fact sheet – damp-habitat detritivores that help recycle nutrients like slugs do.
• Eucalypt forest fact sheet – typical forest habitat where red triangle slugs live under bark, rocks and logs.

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