Their tentacles can reach lengths of up to three metres, and house compartments filled with toxin-filled needles that fire venom when triggered.
It's potent venom can trigger cardiac arrest leading to death within minutes,
Other symptoms include; inflammation, rapid heart rate, difficulty breathing, back pain, and brain hemorrhaging.
But a smaller stinger lurks in Australian waters, and it's near-invisible.
The box jellyfish is the world's most venomous animal with four species — Chironex fleckeri, Carukia barnesi, Malo kingi, and Chironex yamaguchii — considered highly venomous.
The Chironex fleckeri, also known as the Australian box jellyfish is considered the most venomous animal in the world.
And as it's name suggests it's found right here in Australia, in warm tropical and sub tropical coastal waters.
Their range includes the waters north of Bundaberg in Queensland, through to the Northern Territory, down to Exmouth in Western Australia.
A sting from the tiny Irukandji jellyfish, or doom jellyfish, can be deadly.
Irukandji actually refers to any of several similar, extremely venomous species of small box jellyfish.
The series of symptoms caused by a sting have been given its own name; 'Irukandji syndrome'.
Back pain, nausea, abdominal cramps, sweating, hypertension, tachycardia and a feeling of impending doom typically develop 20–60 minutes after the sting.
The inland taipan is found in the remote outback and is considered the most venomous land snake in the world.
Its poison works so fast it can just bite onto prey and just watch it die.
But due to its remote habit, and the fact it spends most of daylight hours underground, not many bites to humans have been recorded.
Australian Museum said only a handful of people have been bitten and all have survived due to "quick application of correct first aid and hospital treatment"
When it's threatened, the blue rings on this pretty octopus "pulsate".
But be warned, they can deliver one dangerous bite — although thankfully, they rarely do so.
This is due to its venomous saliva. It contains a neurotoxin so potent it can kill more than 20 humans in just a few minutes.
Respiratory failure occurs eventually, resulting in death. Other symptoms before this include; feeling numb around the mouth, tongue, face and neck, chest tightness and paralysis.
These aggressive, shiny black spiders live up to a fearsome reputation.
Their bite is extremely venomous and if one is suspected the patient should be taken to hospital in case they need antivenom.
Those big fangs contain a neurotoxin, which attacks the human nervous system.
And due to recent wet weather along the east coast of NSW and south-east Queensland, more are being sighted indoors.
Step on a stonefish, a master of camouflage, and you will regret it.
The fish will pop its spines up and inject it's venom into you; a proteinaceous toxin.
The result?
Intense pain, respiratory weakness, damage to the cardiovascular system, convulsions and paralysis.
If enough venom is released and treatment not sought it can sometimes lead to death.
The fish are found in shallow waters in the Pacific and Indian Oceans.
The saltwater crocodile has been an apex predator for millions of years.
In fact, its the world's oldest and largest reptile alive today.
With teeth that big it's easy to see why.
They are territorial, aggressive and data shows they are responsible for 99 attacks on people since 1971. Of these, 27 per cent were fatal.
Most recently, a Northern Territory man was hospitalised after a crocodile attacked him as he was spear-fishing.
Meet the second most venomous land snake in the world; the eastern brown snake.
An untreated bite can potentially kill in under half an hour as it's venom is a cocktail of dangerous chemicals.
One is a neurotoxin which attacks the nervous system. The other is a procoagulant, which leads to blood clotting and thrombosis.
And the babies are just as dangerous as the adults - if not more so.
A NSW snake catcher, Sean Cade, told 9News last month "venom is venom".
"No matter if the snake is 20 centimetres or six foot it's the volume that causes issues with humans," he said.
"In general, adults can regulate their venom and deliver a dry bite as a warning, but a baby, because they're more frightened, they can deliver several drops."
They are striped when they're young to aid with camouflaged. Their colouring can range from orange to brown.
With its dagger-like talons, powerful kicks and helmet-like crest, the cassowary is considered the world's most dangerous bird.
It's found in tropical rainforests north-east of Queensland, as well as in Papua New Guinea and surrounding islands.
It's one of the closest living species to dinosaurs as its ancient relative evolved shortly after the extinction of the mega-reptiles.
With fewer than 4,600 of these birds left in the Australian wild, they're listed as endangered.