Not all introduced snails wreak havoc. Several species of alien subulinids have arrived in the country over the years and become established without causing too much damage. (Apparently.)
At a smidgeon over two centimetres long, Subulina octona is the largest of the three (or four?) introduced and two native species. It is a tropical tramp, hitching rides on cargo. In Australia, populations are known from locations all over the country. The species is particularly abundant in the Top End of the Northern Territory and parts of Queensland. (But I took this photo on Rakata—the island formerly known as Krakatoa.)
Wherever there's one Subulina, there's bound to be more. They aggregate under rotting logs and drifts of leaf litter. This clustering behaviour seems to be encouraged by chemical cues in the mucus. It's not clear whether they do this to conserve moisture or gain protection from predators. Or maybe they just do it for the company.
D'Avila, S., Dias, R.J.P. & Bessa, E.C.D. (2006). Aggregative behaviour in Subulina octona (Bruguiere) (Mollusca, Subulinidae). Revista Brasileira de Zoologia 23(2): 357–363.
Solem, A. (1988). Non-camaenid land snails of the Kimberley and Northern Territory, Australia. I. Systematics, affinities and ranges. Invertebrate Taxonomy 2(4): 455–604.