After extended periods of heavy rain such as we have experienced recently, householders in the Moggill Creek catchment are often disconcerted at night when viewing wet wooden decks or poolside decking or pavements. Moving slowly across the wooden boards or pavements, often in the rain, a large bright white slug with a peculiar red triangle across its back can sometimes be observed, leaving a scribble-like grazing mark as it removes algae across the flat surfaces.
This unusual, white-coloured unpaid deck cleaner is the Red Triangle slug (Triboniophorusgraeffei), a familiar sight for those with outdoor decking within the Moggill Creek area. It is a large native mollusc, indeed, at 7 cm long it is the largest native slug in Australia.
Active during extensive rain periods, and very prominent during the March 2022 rainfall event, this species hides in cool damp locations (such as deep within rockeries or humid exterior pipes), contracting its body to further minimise water loss. It is always remarkable how such a soft-bodied creature apparently spontaneously appears after dry and hot periods in western Brisbane.
Red Triangle slugs can be readily distinguished from non-native slugs, as they only have a single pair of tentacles on their head, while all other introduced species have four. While the variety most commonly observed in the Moggill Creek catchment is white, yellow and red-bodied forms are also known from the Greater Brisbane region. The foot of the slug often has a red border.
The breathing pore, or pneumostome is present within the boundaries of the distinctive thin red triangle on the slug’s upper body.
These soft-bodied creatures bury themselves in leaf litter during the day, and at night come out to feed, especially if heavy rains or persistent wet weather make it possible for them to traverse hard surfaces, such as decking. They graze on microscopic algae and moss forming on tree bark, wooden structures and rocks. They leave behind scalloped grazing marks, somewhat circular and irregular in pattern, that are often remarked upon when seen on the pale trunks of smooth-barked eucalypts.
It is thought that this species can live for up to three years.
This native mollusc (and many others like it), can be discussed with the Snail Whisperer, Dr John Stanisic at the next MCCG Kid’s Day Out at The Cottage, scheduled for June 2024.
Red Triangle Slug (Triboniophorus graeffei) – photo David Lochlin
Red Triangle Slugs (Triboniophorus graeffei) – photo ‘eyeweed‘