This Leopard Slug appeared on our deck this morning.
My brief research tells me they are native to southern Europe but now can be found pretty well worldwide. They are well distributed over Australia but southern Victoria seems to be a bit of a hot spot for them. (Link - Museum Victoria)
Leopard Slugs are more or less harmless by all accounts and in fact are credited with regulating populations of other slug species by preying on them.
They like to feed on living and dead plant material and fungi too and it seems they are attracted to leftover pet food and faeces.
I found a quote from the Mollusc of the Year (?) – "On the one hand many people will think slugs to be disgusting and harmful. On the other especially the Leopard Slug is a species of striking beauty and elegance …" Mrs Gouldiae does not agree!