When its tentacles are extended, the blue-ringed octopus measures only about 20 centimetres and weighs about 50 grams. It is, however, one of Australia's most venomous creatures. Its saliva contains a neuromuscular poison so potent that it causes immediate respiratory paralysis and death can occur within an hour and a half.
    Found in all Australian states, there are two species of this octopus: the larger tropical species, Hapalochlaena Irrnulata and the common southern species, H. mactrlosa. The differences between the two are only minor.
  The blue-ringed octopus is quite small and rarely exceeds 20 centimetres from the tip of one arm to the tip of another. Like other octopuses it has many cup-like suckers on its arms which allows it to pick up objects. Its diet is mainly crustaceans, particularly crabs and molluscs.
    Poisonous saliva The blue-ringed octopus has two large salivary or venom glands situated above its brain. A duct leads through the brain into its mouth parts which terminate in a small, parrot-like beak situated at the junction of its eight arms.
    When hunting a crab, the octopus swims over it and sprays its poisonous saliva into the sea immediately surrounding it. The crab absorbs the poison and becomes paralysed within minutes allowing the octopus to seize and devour it.

    The blue-ringed octopus is usually found in rock pools around the Australian coast. When not hunting for food it sometimes shelters in rocky holes and old shells which offer protection from large predatory fish. Snapper, groper, shark and moray eels are particularly fond of octopus. The blue-ringed octopus hunts at night. They are often washed up into small, inshore pools when the tide is rising where they may bite children or uninformed adults who may pick them up.

    When undisturbed the blue-ringed octopus has dark brown ochre bands over its arms and body, with blue circles superimposed on these bands. When the animal is disturbed in any way or taken out of the water the colours darken and the rings turn a brilliant electric-blue colour. This dramatic and beautiful colour change and the animal's small size helps to identify it. The blue-ringed octopus should never be picked up or touched in any way, except by those trained to do so.

    Strangely enough the bite of the blue-ringed octopus is usually painless to human beings and oftentimes goes unnoticed. However, its devastating effects are almost immediate and sometimes  fatal.  Extensive  studies  of the  venom  suggest that the main component is similar to the toxin found in the flesh of many poisonous fish such as toad or puffer fish. The poison interferes with the movement of impulses down the nerves of the body.
    Symptoms of the bite include numbness of the mouth and tongue, blurring of vision, loss of tactile  sensation,  difficulty  with  speech  and swallowing, paralysis of the legs and nausea.
  If the victim is not treated, paralysis may occur within minutes, followed by unconsciousness and death can follow from heart failure due to lack of oxygen.

    Full first aid must be applied as soon as possible, but  it  is  worth  noting  here  that  no antivenom exists for the blue-ringed octopus. In the event of a bite from this creature, it is usually essential to carry out mouth to mouth resuscitation and cardiac massage until the effects of envenomation have subsided. This may take several hours, but quite simply means the difference between life and death for the victim. #    ·