Mar 2019

Docile but Deadly – The Blue Ringed Octopus

By Mike Waddington

Recently, we created a blog post about some of the most venomous animals in the ocean, which included some unlikely contenders, such as the textile cone snails and flower urchins.

That list also featured an animal that is so often misunderstood, and feared by non-divers due to its potentially lethal bite, yet sought after by divers for its docile behaviour, striking colouration and mesmorising beauty.

We are of course talking about the ultimate macro critter, the blue ringed octopus.

What is a Blue Ringed Octopus?

The Blue Ringed Octopus is a common term for four highly venomous octopus species that are part of the genus Hapalochlaena.

As far as octopuses go, they are relatively small. The smallest species can reach a maximum size of around 12 centimetres (body and arms) while the largest species, the Southern Blue-Ring can reach a maximum of 20 centimetres.

All four species are native to the Indo-Pacific, and can be found as far west as Sri Lanka, as far south as Southern Australia, and they can be found throughout some of the western Pacific archipelagos.

Although there are currently four described species, there are six more possible species that are currently being researched.

What does a Blue Ringed Octopus Look Like?

Members of the genus Hapalochlaena are instantly recognisable from their striking colouration.

Much like other octopus species, the colouration varies depending on the individuals current circumstances and environment. When resting, the octopus will take a dull, brownish colour, and the rings will be dull.

It is when the octopus makes a move that it shows its true colours. To warn potential predators of its lethal bite, the blue-ringed octopus will alter its body colour to bright yellow (almost gold), and electric blue rings. If it feels threatened, it can increase the contrast of the blue rings by changing the colour surrounding the rings to black. The number of blue rings can vary between species and individuals, however it is normally around sixty. They also have blue lines running through their eyes.

Although the different species have names such as “greater blue-ringed octopus” (H. lunulata) or “lesser blue-ringed octopus” (H. maculosa) this name does not have any correlation to size of the species, but rather to the number and size of the blue rings.


Blue-Ringed Octopus Behaviour

All species of blue-ringed octopus are known to be docile, and will only ever attack if they feel severely threatened.

They spend most of their time hiding in cracks and crevices, using their chromatophores to blend in with their surroundings. They will also gather rocks and rubble around their lair to block any entrances so predators cannot get to them. They are active both during the day and night, however they tend to feed more during the day, and at night they are moving around the reef looking for potential mates or a better lair.

To move around the reef, they will usually crawl over the substrate, feeling inside the crevices with their arms to find food. When moving slowly, they will usually still be camouflaged, however when approached, they will flash their warning colours, and the more threatened they feel, the more contrasting the blue rings will be.

Like most animals, fleeing is their first defence mechanism. If they need to make a quick escape, they can move by jet propulsion by expelling water from funnel on their underside. They can also release ink to help hide themselves while they look for a safe place to take cover.

What does a Blue-Ringed Octopus Eat?

Like other octopus species, all species of blue-ringed octopus are carnivorous, feeding on a diet that consists mainly of small crustaceans such as crabs, shrimp and bivalves. They will also feed on small fish is they can catch them, however most fish species are too quick for the octopus.

To catch their prey they pounce on them, gripping them with their arms and pulling them towards its beak. Any soft bodied prey will be bitten immediately, injecting it with its venom, and then eaten once the victim has become paralysed. For hard bodied prey like crabs, they will use their sharp beak to penetrate the exoskeleton, and release the venom into the exposed flesh. For creatures with tougher shells, such as bivalves, the blue-ringed octopus will drill a hole into the shell with its beak, inject the venom, and then suck the flesh out of the hole it drilled.

Why are Blue-Ringed Octopus so Toxic?

Despite its miniature size, all species of blue-ringed octopus are extremely venomous. A single octopus carries enough venom to kill twenty-six fully grown humans in a matter of minutes. What is particularly interesting is that the venom is not produced by the octopus itself, but rather by a bacteria that lives symbiotic in the salivary glands of the octopus.

The main compound in the venom is known as tetrodotoxin, and its more than 1,200 more toxic than cyanide. It works by blocking the sodium channels, causing respiratory arrest and motor paralysis within only a few minutes of being bitten. The venom will paralyse all voluntary and involuntary muscles, often resulting in death due suffocation caused by paralysis of the diaphragm.

Tetrodotoxin is also famed as the poison found in the flesh of pufferfish and the mucus membrane of some species of poison dart frogs.

Blue-Ringed Octopus Treatment

The bites themselves are usually painless, so the victim does not realise they have been bitten. It isn’t until paralysis begins to kick in that the victim knows something is wrong, and by this point it is too late to call for help. There is no anti-venom available for tetrodotoxin, but that doesn’t mean the victim is completely helpless.

If someone knows, or suspects, they have been bitten by a blue-ringed octopus, they must alert someone and get ready for the quick onset of paralysis.

Because the victims diaphragm is paralysed, artificial respiration must be administered quickly, before cyanosis occurs due to lack of oxygen. This artificial respiration usually takes the form of rescue breaths until medical assistance arrives, and the victim can be put onto a respirator. If rescue breaths are administered in a timely fashion, the victim will most likely survive and make a complete recovery.

Are Blue-Ringed Octopus Dangerous?

This is a very common question, and a tough one to answer,

They are extremely docile animals, and will very rarely bite a human, even when threatened. They can be found throughout most of the Indo-Pacific and yet bites are extremely rare. There have been at least three reported deaths – two in Australia and one in Singapore – which is very few considering how many people must swim close to them each day.

The answer is probably yes and no, depending on how you interact with them.

There is no reason to avoid them and not go into waters where they are known to live, however you should always be careful and never stick your fingers into any crevices on the reef, nor should you lift rocks from tide pools.

As with anything underwater, you should just follow the basic rules of not touching, prodding or harassing them, and you should be fine. If you are lucky enough to see one, and it starts flashing its warning signals, it is a good idea to leave it alone and give it some space, just in case it feels overly threatened.


Where Can I Dive with a Blue-Ringed Octopus?

Although they can be found throughout most of the Indo-Pacific, your best chances of finding them are in places such as:

  • Mabul, Malaysia
  • Lembeh, Indonesia
  • Raja Ampat, Indonesia
  • Kimbe Bay, Papua New Guinea
  • Anilao, the Philippines
  • Sydney, Australia
  • Melbourne, Australia

They prefer to live in rubble areas as they will have more places to hide. They can be found on coral reefs, however with so many potential hiding spots, they can be very difficult to find. It is far easier to spot them on barren sandy slopes as there are far fewer places for them to live.

A good dive guide is almost essential for finding blue-ringed octopus.

These beautiful creatures frequently make the top of most divers bucket lists, and it is easy to understand why. After all, how many people can say they came face to face with one of the most venomous creatures on the planet.

Have you ever seen a blue-ringed octopus? If so, we would love to hear from you. Let us know where it was and when in the comments section below.

‘Docile but Deadly – The Blue Ringed Octopus’ was written by Mike

Photo Credit:

Get the latest deals straight to your inbox.

Mike Waddington

I first discovered diving in 2008 after going snorkeling on the Great Barrier Reef in Australia. After trying diving at a flooded quarry in England I decided to head out to warmer more interesting waters in Thailand where I ended on the Island of Koh Tao completing my Open Water course. Instantly addicted with money to spend and plenty of time on my hands I decided to continue until I became a Divemaster so I could live what seemed as the perfect life.

After that I headed to the Caribbean to an island called Utila to complete my instructor course, I spent several months out there completing the MSDT internship, teaching students and leading dives. This is also where I discovered my interest in the technical side of diving, taking part in equipment repair courses and learning about blending gasses and running compressors.

With all my new qualifications it was time to head back to where it had all started, Back to Koh Tao where I intended on living the dream. Once I arrived I quickly found a job and started teaching straight away. During my time on Koh Tao I took part in all many technical diving courses, learning how to dive with re-breathers, in caves and even going down to 90m/300ft!


PADI Master Scuba Diver Trainer
PADI/DSAT Tech Deep Instructor
PADI/DSAT Gas Trimix Gas Blender
PADI/DSAT Trimix Diver
TDI Intro to Cave Diver
TDI Advanced Wreck Diver
TDI Inspiration rebreather Decompression Procedures
PADI Professional Videographer
BSAC Compressor Operator
TDI Equipment Service Technician

Dream Dive Locations:

Silfra, Iceland
Cenotes, Mexico
Chuuk Lagoon, Micronesia
Ice Diving in Russia