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Cute But Deadly

By Alex Campbell on May 17, 2011 in Other

Ask anybody to name a dangerous marine animal and most will hark “shark”, but one of the deadliest critters on our beaches is also one of the prettiest. Blue-ringed octopuses (several species within the genus Hapalochlaena) are adorable, miniature octopi (about the size of a golf ball), with beautiful, iridescent blue markings and a national distribution, found within rock pools, crevices and empty bottles all around Australia’s coastline. Although characteristically timid and shy, if you upset one of these little guys, they sure pack a powerful punch.

Being a small, soft, delicious cephalopod (a biological class including octopuses and squid) floating around the ocean has its drawbacks. For starters, most of your neighbours want to eat you. The enigmatic blue-ringed octopus solves this persistent problem with several innovative strategies. Firstly, it hides. Blue-rings live in small, inaccessible spaces, out of view and reach of hungry eyes, tentacles and ganglia.

They are also experts in camouflage. In fact, many cephalopods can rapidly and almost perfectly blend in with their surroundings by changing shape and colour, the latter using specialised light-reflecting, pigment-containing ‘chromatophore’ cells on their body surfaces. Secondly, blue-ringed octopuses invest a lot of energy into chemical warfare: armed with two giant venom glands (as big as their brain), these little guys can easily incapacitate and catch prey with one type of venom and completely overcome would-be attackers with the other.

Despite its small size and cute, innocuous appearance, the average blue-ring carries enough venom to kill up to 26 adults within minutes. Although its first reaction to being disturbed or threatened is to flatten, hide and avoid conflict, continued provocation will result in an impressive, albeit deadly, colour change. From camouflage brown, it will turn bright yellow with its brilliant, iridescent blue rings flushing and pulsating: a first and final warning.

Although they can penetrate a wetsuit, you might not even notice the painless bite of a blue-ringed octopus. However, within ten minutes you’ll certainly feel the symptoms. In the animal’s saliva is a powerful neurotoxin called tetradontoxin, which is also found in the venom of stonefish and cone shells. Once this makes its way into your blood stream you’ll feel weakness, numbness and nausea. Following this, tetradontoxin causes complete motor paralysis by shutting-down sodium channels in your nervous system. A victim may be unresponsive with fixed, dilated pupils, but still be fully conscious and aware of what you’re saying. These bites are particularly life-threatening because with such total paralysis, the cardiovascular system shuts down and patients go into cardiac arrest, usually dying from a lack of oxygen.

Although there is no known antivenin for blue-ringed octopus bites, first aid involves compression and immobilisation of the bite site and prolonged assisted ventilation (e.g. using CPR or mechanical ventilation in hospital). Remarkably, despite its rapid and extreme effects, the venom is usually processed by the body (if the patient receives appropriate ventilation support) after about 24 hours and in most cases has no side effects.
So if you see a pretty little octopus in a rock pool, look but definitely do not touch.

To hear more from Alex and get a weekly fix of scientific, environmental and health-related info, tune-in to ‘Boiling Point’ on 89.7 FM Eastside Radio every Tuesday at 6.00pm, stream online at, find us on Facebook or e-mail


  1. I’ve been told that the ‘Fijian’ blue ringed octopus is not toxic. Is this true?

    Posted by: P cooper | March 2, 2013, 7:45 PM |

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