The platypus and echidna both have venomous defence systems. As far as snakes go, Australia is home to the ten most lethal in the world. Sturan Sutherland reckons that of the world's top 25 venomous snakes, Australia has 21. This article imples that the black mamba is as venomous as the taipan . A really good overview of lethality of a range of snakes is available on Sean Young's excellent snake site .
Many venoms have multiple components or toxins that lead to a complicated clinical picture.
Most affect autonomic and skeletal nerves but also may interfere with other parts of the nervous system and smooth muscle. Neurotoxins Neurotoxins are responsible for the majority of symptoms following Australian snake bites. Postsynaptic toxins All Australian snakes have at least one low molecular weight postsynaptic neurotoxin. They are rapid in onset and their action often causes the prodominant clinical picture. Fortunately, these effects are usually rapidly reversed by anti-venoms.