Ticks and other things that sting, suck and bite.
The saliva has a presynaptic neurotoxin that causes an ascending motor paralysis.
There is no evidence that leeches transmit disease to humans and they are found in all states of Australia.
It causes severe pain and later can cause hyperaesthesia and possibly weakness. The venom is used by the male platypus when fighting with other males (during mating season) and causes transient paralysis. The few cases that people have been poisoned it has not resulted in death.
Generally scorpions are nocturnal so most stings occur at night. Systemic symptoms rarely occur and are mild. The scorpion shown is the specialist spider eater.
Cane toads excrete a toxic venom. It is used when smoked---unwisely---as a hallucinogenic drug. Below is a link to a truly great 1988 Cane Toad documentary.
Typically found along the east coast ---think Brisbane, Sydney and Canberra.
They can jump--but only 10cm. Their venom is highly immunogenic and anaphylaxis was the cause of those 4 deaths.
Found all around Australia they cause local pain which can vary from being like a wasp sting to being much more severe. Australian centipedes have between 15 and 191 pairs of legs---so they are poorly named (Centi 100 pede legs).
Its toxin is over its skin which is why it does not have any natural predators. The colours are a warning. Numbers have been rapidly dropping after being abundant in the 1970s.
The Amazonan leech grows up to 450mm. The photo comes from a video of a pet giant leech that used to snack on its owner.
Below is a link to an interesting but gross video of a leech that was in the patients throat/sinus being removed under GA.