The bright-blue octopus with tiny toxic tentacles

Despite only growing to five-inches long the blue-ringed octopus is quite possibly the most deadly cephalopod in the ocean with a toxin 1000 times more potent than cyanide.

blue ringed octopus
A blue-ringed octopus shows off how it gets its name

Named after the psychedelic patterns that appear on their skin when threatened, Blue-ringed octopuses are one of the most colourful cephalopods you will find in the ocean. They are also quite possibly one of the most adorable growing to a max length of only five inches. But whilst they may be small enough to fit in the palm of your hand, they’re also toxic enough for that to be one of the last things you ever want to happen. A couple of close calls with tourists in recent years have some people on edge. But these colourful characters are just another example of how interesting and surprising octopuses can really be.

More than meets the eye

Blue-ring octopuses can be found across the Pacific and Indian oceans living in tidal rock pools or on coral reefs. In terms of basic physiology and behaviour they are extremely similar to other members of the octopus family. They spend a majority of their time hiding in crevices using their boneless bodies to squeeze through tight cracks and dermal chromatophore cells to change colour and camouflage expertly. When they do feed they eat crabs, shrimp and other crustaceans along with some small fish. They swim via jet propulsion and have the tentacles, beak and body shape that is synonymous with octopuses. However what really stands them apart at first glance is their size. They grow to around five inches long and have a relatively short lifespan of around two years. Despite their name they will normally appear yellow in colour and could easily be confused as a juvenile of one of the more common species. But they possess several qualities that make them much more intriguing and dangerous than any other octopus.

A terrifying toxin

Unknown to a majority of people most cephalopods including all octopus, most squid and even cuttlefish are venomous to some degree. But the blue-ringed octopus takes toxicity to a whole new level. It produces a powerful neurotoxin called tetrodotoxin that is more lethal than any poison found above the surface of our oceans. It is a thousand times more lethal than cyanide and has no known antidote. They use it to hunt their prey almost effortlessly but with devastating efficiency. It works by blocking nerve signals throughout the body associated with muscle control leading to blindness, paralysis and eventually suffocation when the victim can no longer breathe. All of which can happen in a matter of minutes. This means the blue-ringed octopus only has to bite its prey once before it is immobilised and dies, leaving an easy meal for the octopus. Some pufferfish can also produce tetrodotoxin as a defence mechanism but the blue-ringed octopus is believed to be the only animal that uses it for predation.

Tetrodotoxin is possibly the most deadly natural toxin produced in nature (chemical diagram)

Bright blue rings

So where do their infamous blue rings come from? Well they only appear when threatened by larger predators such as groupers or small sharks. When such interactions occur between 50 to 60 bright blue rings will appear across the octopus’s body within a third of a second. On full display the patterns appear almost psychedelic and glowing. That is because they contain multi-layer light reflectors called iridophores which shine blue/green light back towards any potential predators. Becoming brightly coloured in the presence of predators may seem like an unlikely way to avoid being eaten. But it is actually mutually beneficial to both the octopus and any hungry sharks or fish. The colouration is what is known as an aposematic warning display and basically tells any predators that eating the octopus would be equally deadly for both parties due to their potent neurotoxin. As a result predation of blue-ringed octopuses is actually quite rare.

A closer look at the luminous bright blue rings that warn off predators

Public menaces?

There have been several documented cases of near misses when it comes to blue-ringed octopuses and humans. There is enough tetrodotoxin within a single octopus to kill 26 fully grown men and as a result a bite will almost inevitably lead to a fatal outcome. Two such close calls happened earlier this year in Australia where on both occasions people were lucky to escape unharmed. In January an 11 year old girl from Sydney was almost bitten by a blue-ring that had made its home in a shell she was carrying to her mother. Fortunately she dropped the shell when a tentacle emerged and her mother identified the poisonous cephalopod for what it was.  A month later a video of an oblivious tourist holding a blue-ringed octopus went viral as the unaware traveller joked around miraculously managing to avoid getting bitten. Because of the attention these stories received Australian authorities now issue warnings to the public to avoid certain beaches when blue-ringed octopuses appear. However they only really pose a threat when people get too close or provoke them like most wild animals.

close call
What is he doing?! People in Australia went crazy after watching the viral video of a tourist handling a blue-ringed octopus

Surprising cephalopods

The blue-ringed octopus is just another example of how interesting and misunderstood octopuses and other cephalopods really are. They are one of the oldest groups of marine animals having remaining relatively unchanged in around 300 million years. Yet over that time they have amassed an array of amazing adaptations to help them survive and thrive. Although they are sometimes stigmatised or appear alien to us they are actually one of our closest intellectual rivals. Multiple studies have highlighted their intelligence and problem solving ability and despite having drastically different brains to us have even been shown to behave in an almost identical way when exposed to some drugs such as MDMA. Hopefully there is much more we can learn from these amazing creatures in the future.


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