Triangle Slug at Mount Coolum
Author: Frank McGreevy, Sunshine Coast Branch
Published: Journal December 2016
Early Saturday morning, 11th June 2016, strong winds blew over an old, dead Macaranga in my backyard at Mt. Coolum. On investigating the trunk and peeling off some bark about 2.5 metres from the base, I discovered a Red Triangle Slug (Tribonio-phorus graeffei Humbert, 1863) 70mm long and 40mm wide, which when moving became 85mm long and 25mm wide!
Apparently, it lives in rainforest and eucalypt woodland, buried in the ground under logs and rocks during the day and crawling on tree trunks at night, particularly after rain, leaving lines of small circular markings on smooth-barked eucalypts after feeding. A herbivore, it feeds on algae and fungi living on tree trunks, rocks and leaf litter on the forest floor.
The species is oviparous, laying soft spherical eggs in a small cluster. Only the one genus with one species is found in Eastern Australia.
The single genus, Tribonio-phorus, is found from the Illawarra District of NSW up the Australian East Coast into Papua New Guinea, also Irian Jaya, New Britain, New Ireland and the Admiralty Islands.
A large colour range exists in this species, the most common being bluish grey. On Mt. Bellenden Ker it is bright orange, Mt. Bartle Frere white, and Mt. Kaputar bright red. For colour photos see Stanisic (2010) et al, P373.
Some controversy exists as to whether the family arose in the north and spread south, or it arose in Antarctica followed by a two-pronged northern radiation. Ref. Beesley et al 1998. The jury is still out on this issue and we may never know of an outcome.
The circular feeding marks of Red Triangle Slugs on a Spotted Gum. Photo R. Ashdown.
Bibliography:
Beesley PL, Ross GJB, & Wells A, (eds) (1993) Mollusca The Southern Synthesis, Fauna of Australia, Vol 5, B, CSIRO. Melb. P1109-1110.
Stanisic J, Shea M, Potter O, Griffiths O, (2010) Australian Land Snails Vol 1., A Field Guide to Eastern Australian Species. Bioculture Press; Mauritius, P372-373.
Queensland Museum (2007) 2ed. Wildlife of Greater Brisbane, P20.
EDITOR’S NOTE: The Red Triangle Slug is Australia’s largest native land slug. The distinctive red triangle on its back contains the breathing pore.
Red Triangle Slugs are found in urban areas, forests, woodlands and heath.
The Red Triangle Slug is usually found grazing on microscopic algae growing on the surface of smooth-barked eucalyptus trees, leaving behind scalloped tracks as it goes. If given the chance, it will also remove bathroom mould.