These cute cephalopods that fit in the palm of your hand could kill you in minutes with a venom a thousand times stronger than cyanide, says Melissa Hobson
What are blue-ringed octopuses?
Blue-ringed octopus are a genus of octopus known for their iridescent blue markings. These iconic patterns only reveal themselves when the little octopus – which are smaller than a human hand – get annoyed or feel like they’re in danger, which can lead to cases of mistaken identity when the animals are calm.
They kill prey and defend themselves with their famous bite, which contains a venom one thousand times more toxic than cyanide. This paralyses their prey so they can gobble them up, but it also has a deadly effect on humans. If you get on the wrong side of this tiny creature, you could end up fighting for your life in hospital. Thankfully, bites are rare as blue-ringed octopus aren’t aggressive.
There are several species of blue-ringed octopus and, despite the name, they don’t have blue rings… until they’re riled up.
Where do blue-ringed octopuses live? They are found in the tropical waters of the Pacific and Indian oceans
How big are blue-ringed octopuses? These miniature cephalopods grow no larger than 22cm and weigh up to 100g. Some adults are the size of a golf ball. Although these little critters easily fit into the palm of your hand, they’re not to be underestimated. Blue-ringed octopus are one of the most venomous creatures on the planet.
What do blue-ringed octopuses look like? Like other octopuses, they are marine molluscs. They have a large mantle (head) which contains their organs and eight flexible arms with strong suckers that they use to move and grab onto things. Underneath their body – where these eight arms converge – is the octopus’ mouth.
They have a hard beak – like a parrot – that’s capable of crunching through hard-shelled prey. If you get too close to a blue-ringed octopus, this beak is the part that will do you in. Their bite might feel like nothing more than a small peck – reportedly, it’s no more painful than a bee sting, if you feel it at all – but their saliva contains a venom that can kill you within hours, or even minutes.
Usually, these little octopus are a brown, tan or creamish-yellow colour to help them blend into the seabed around them. They only show off their blue rings when they feel in danger. When dazzling sapphire rings appear all over their body, they’re warning predators to keep away. This is called aposematism.
How do their blue rings appear?
Octopus have special cells called chromatophores underneath their skin that allow them to change colour. Like a water balloon filled with coloured dye, when these chromatophores squish down into a tiny space you can’t see the colour inside.
When they stretch out, the pigment can be seen and the animal’s skin colour changes before your eyes. This remarkable colour-change can happen in an instant. When they reveal their hidden pigment to display their bright cobalt rings, a peeved blue-ringed octopus can give predators a sign that they’ll be in trouble if they come any closer.
Why are blue-ringed octopuses so dangerous?
When these teeny tots bite you, they deliver a dangerous venom. TTX is a neurotoxin so potent that it’s said to be about 1,200 times more deadly to humans than cyanide. There’s no known antidote for a bite so the only thing doctors can do is treat the symptoms – for example, by putting you on a ventilator – and hope the patient survives.
Thankfully, death by blue-ringed octopus isn’t common (although a string of bites were reported on Balmoral Beach in Sydney, Australia, in early 2025). According to the Natural History Museum, there have only been “a handful” of fatalities from a bite from these venomous beasties.
What happens if you get bitten?
It’s rare, but not unknown, for humans to be bitten by a blue-ringed octopus. These little creatures aren’t aggressive and will only bite when they feel threatened. But if they do defend themselves, you could be in serious trouble.
Bites usually happen when someone accidentally steps on, disturbs or tries to handle the octopus while tide pooling or at the beach. It doesn’t usually hurt but you might (if you’re lucky) feel a little nip or notice a spot of blood on the area before experiencing the first symptoms.
These include tingling and numbness of the face, lips and tongue, feeling lightheaded and sweating. If you suspect you have been bitten, get to a hospital immediately for medical help as the toxin works quickly. Before long, the patient could experience nausea, vomiting, muscle weakness and paralysis, which can lead to coma and death.
Death can occur after a day or as soon as within 20 minutes.
What do they eat?
These cute cephalopods usually feed on crustaceans, such as crabs and shrimp, as well as small fish. They are nocturnal ambush hunters so they come out at night to find food. Once they’ve set their sights on their unsuspecting victim, they creep up on it then – bam – grab it and take a bite. As they chomp into it, they deliver a powerful venom called tetrodotoxin (TTX) through their saliva. This paralyses the prey so the blue-ringed octopus can enjoy its meal. TTX is also poisonous: as an extra defence if a predator tries to eat them.
How long do they live? Their average lifespan is around two years
Are they under threat?
Blue-ringed octopus aren’t categorised as endangered or vulnerable on the IUCN Red List of Threatened Species. However, scientists aren’t sure how climate change and human activities – such as urbanisation and pollution – are affecting them.
As sea surface temperatures rises, many animals in the ocean are struggling to survive in the warmer waters or adapting by moving to new areas. Only time will tell how these diminutive molluscs will fare in a changing climate.
This article by Melissa Hobson was first published by Discover Wildlife on 7 March 2025.
What you can do
Wildlife continues to face threats from overexploitation in the form of poaching and illegal trade in animal products, as well as a rapidly changing climate.
Due to growing threats, 70% of all animal and plant species are at risk of extinction by 2050.
With your donation, our conservation partners can continue to motivate millions of people worldwide to take action that protects and preserves wildlife at risk.
Donate
Leave a Reply