(Okay. I might have plummeted straight through hyperbole into the pit of ... well ... lies. Oncodamus isn't dangerous. Not to humans, anyway. It's also really quite small.)
You've probably seen a spider like this—red front end and a black bum. It belongs to Nicodamidae, a family found only in Australia, New Guinea and New Zealand. Until arachnologist Dr Mark Harvey got his hands on the group, it was thought to contain only ten species (twelve at a pinch) in two genera. Then he published a revision of the family and pushed the number up to 29 species in nine genera. All that time, we'd been seriously underestimating the natty nicodamids.
This fellow from Lake Eacham probably belongs to Oncodamus decipiens, a species only recognised as recently as 1995. Although it occurs from Barrington Tops in New South Wales to Mount Spurgeon in Far North Queensland, it is restricted to patches of rainforest. This distribution resembles that of many other species, including the red triangle slug (Triboniophorus graeffei). (RTSs are a great favourite of this blog. In case you haven't got an eyeful yet, David Nelson is a bit keen on them too.) It may be that what we currently know as Oncodamus decipiens is actually made up of a bunch of species. But that's probably a question for the gel jocks.
Harvey, M.S. (1995). The systematics of the spider family Nicodamidae (Araneae: Amaurobioidea). Invertebrate Taxonomy 9: 279–386.