Okay, here’s the skinny:  The reason Australia has so many cute, cuddly creatures like koalas and kangaroos is that there are very few dangerous animals in Australia to bother them.  Remember, at one time, the whole world was filled with marsupials like the kangaroo, but they all got eaten up by the lions and tigers and bears.  Fortunately, there are no lions, tigers, or bears in Australia.

There are, however, some critters that us humans could definitely do without, especially if we decide to take a swim on one of Australia’s thousands of beaches.  

I. The Sea Wasp

The Sea Wasp or the box jellyfish is one of the most deadly stinging animals in the sea. The sea wasp has a large transparent body shaped like a box or a bell, that can be as large as a bucket, and can weigh as much as five pounds. A cluster of 16 long semi-transparent tentacles stream out from under the bell of the box jellyfish. Millions of stinging capsules cover each of the tentacles. The stinging capsules discharge lethal poison into the skin of any creature that touches them.  Children who have been stung by the sea wasp have died within minutes of being stung.

II. The Portuguese 
Man-Of War

The Portuguese Man-Of War is another stinging jellyfish, and although it is much more widespread and common than the box jellyfish or sea wasp, it is not as deadly as the sea wasp. The Portuguese man-o-war is commonly called the blue-bottle in Australia.  Actually, the Portuguese man-o-war is not a single marine animal, but consists of a large colony of smaller marine organisms. The blue-bottle gets its name from the body, which really is a large, gas- filled float. The float has a crest, that is used much as a sail to propel the colony across the water when the wind blows.  Although the sting from the Portuguese man-o-war is not deadly to humans, a person who comes into contact with a Portuguese man-o-war or blue-bottle will still experience a sharp severe pain.

III. The Blue-Ringed Octopus

The Blue-Ringed Octopus is another one of the smaller, but more deadly marine animals that inhabit the coastal waters around Australia. The blue-ringed octopus is normally light in color, with dark brown bands over its eight arms and body, with blue circles superimposed on these dark brown bands. When the octopus is disturbed or taken out of the water, the colors darken and the rings turn a brilliant electric-blue color, and it is this color change that gives the animal its name. The blue-ringed octopus secretes a very deadly poison, either by biting with its parrot-like beak, or by squirting the poison into the water surrounding it.  The direct bite from the blue-ringed octopus is usually painless,  but the deadly effects of the poison will be noticed immediately. The poison apparently interferes with the body's nervous system. The victim will immediately experience numbness of the mouth and tongue, blurring of vision, loss of touch, difficulty with speech and swallowing, and paralysis of the legs and nausea. If the victim does not receive medical treatment immediately, full paralysis may occur within minutes, followed by unconsciousness and death due to heart failure and lack of oxygen. There is no antivenom for the poison from a blue-ringed octopus. It is usually necessary to perform continuous CPR on a victim until the effects of the venom have subsided. This may take several hours, but it may mean the difference between life or death for the victim.

IV. The Saltwater Crocodile

The adult saltwater crocodile will eat anything that comes too close to it. That includes fish, birds, and mammals of any size, including humans, that venture near the water's edge.

Even though the crocodile looks like it should be clumsy on land, the saltwater crocodile is extremely fast, and it is, of course, an excellent swimmer and an expert at camouflage. Crocodiles can actually outrun a horse over short distances.

V.  Sharks

Many kinds of sharks live in the warm waters around Australia, like the Whale shark, the Basking shark, the Oceanic White-Tip shark, Dusky shark, Leopard shark and the Hammer shark.. However the largest and most scary, the Great White, is also the most common shark in Australian waters.  The smallest shark is the Dwarf shark, and the largest is the Whale shark.  As dangerous as they can be, most sharks will not attack humans unless bothered, and actually, sharks themselves don’t have an easy time of it. Dolphins attack sharks in groups to protect their young. The shark's biggest enemy is humans who attack sharks for food, sports and to protect beaches.  Sharks appear to be smooth, but up close they have sharp points that are tough. A sharks' body is also streamlined so they can move quickly and easily through the water.  Sharks eat other sharks, seals, fish, baby dolphins, birds and sometimes humans…mostly because they mistake them for seals.

On dry land, the danger is mostly from snakes and insects.  And, as a matter of fact, Australia claims to have more species of venomous snakes than any other continent on earth,  and a collection of spiders which are also among the world's most poisonous.  Ugh.

I. The Red Bellied

The Red Bellied Black Snake grows to about three feet in length. Its upper surface is glossy black and its underside is red. It is found near streams and lagoons of eastern Australia. It hunts by day, feeding on frogs, small mammals and other reptiles. Its venom is dangerous to man.

II. The Tiger snake

The Tiger snake is one of the deadliest snakes in the world, and can be found in the Australian Southwest. The body and tail can be a greenish brown, brown, olive dark brown or blackish brown with distinctive bands that are greenish, grey-white or yellowish white.  The Tiger snake shelters in or under fallen rotten timber; under rocks, in deep dense matted vegetation and in empty animal burrows. It feeds on frogs, lizards, nestling birds and snall mammals.

III. The Taipan

The Taipan is the most venomous snake in Australia. Male and female are both very aggressive if cornered, but for the most part, taipans steer clear of humans. The taipan has the longest fangs of any Australian snake, and can be up to a half-inch long.

IV.  Red-Backed Spider:  

Red-back Spiders are related to our Black Widow Spider.  They are brownish black  with an obvious orange to red stripe on the upper abdomen and an "hourglass" shaped spot on the underside of the abdomen. Females have a body about the size of a large pea and slender legs. 

Red-back bites occur frequently, but only the female bite is dangerous. They can cause serious illness and have caused deaths. Because of their small jaws many bites are ineffective. Common early symptoms are pain (which can become severe), sweating (always including local sweating at bite site), muscular weakness, nausea and vomiting. An antivenene is available. No deaths have occurred since its introduction.

V. The Tree-dwelling Funnel-web Spider

The Tree-dwelling Funnel-web Spideris the most dangerous spider in Australia, and among the most dangerous spiders in the world.They are found from northern New South Wales to southern Queensland, usually in heavily timbered areas which are rarely entered by man.  Interestingly, not all creatures are affected by the poison.  For example, a rabbit can be injected with a large quantity of Funnel-web spider venom without ill effect.  A small dose can be lethal to humans.  The male of this spider is five times more dangerous than the female.