Hazardous Marine Life

Hazardous Marine Life

Blue-Ringed Octopus

Blue-ringed octopus are a small species of venomous octopi that live in tropical tide pools from south Japan to the coastal reefs of Australia and the western Indo-Pacific. These small octopi are the only cephalopods known to be dangerous to humans.


The blue-ringed octopus hardly ever exceeds 8 inches (20 centimeters) in size. Their most distinctive feature is the blue iridescent rings that cover their yellow-colored body; however, it is important to emphasize that this feature is only displayed when the animal is disturbed, hunting or mating. When calm or at rest, the animal may display an overall yellowish, grey or beige coloration without any visible blue rings. The blue-ringed octopus is more active at night, spending most of the day hidden in its nest in shallow areas or tide pools.


Blue-ringed octopus envenomations are very rare. These animals are only endemic to southern Japan, Australia and the western Indo-Pacific. Cases outside of this region are generally due to deliberate handling of aquarium specimens. There are only a handful of reported fatal cases. Full recovery is expected with timely professional medical intervention.

Mechanism of Injury

As with all cephalopods, octopi have a strong beak similar to those of parrots and parakeets. All octopi have some sort of venom to paralyze their victims, but the blue-ringed octopus bite may contain an extremely powerful neurotoxin called tetrodotoxin (TTX), which can be up to 10,000 times more potent than cyanide and can paralyze a victim in minutes. Theoretically, a little more than one-half milligram of this venom — the amount that can be placed on the head of a pin — is enough to kill an adult human.

Certain bacteria present in the blue-ringed octopus' salivary glands synthesize the toxin. TTX is not unique to the blue-ringed octopus; certain newts, dart frogs, cone snails and pufferfish can also be a source of TTX intoxication, though from different mechanisms.

Signs and Symptoms

A blue-ringed octopus bite is usually painless or no more painful than a bee sting; however, even painless bites should be taken seriously. Neurological symptoms dominate every stage of envenomation and manifest as paresthesia (tingling and numbness) progressing to paralysis that could potentially culminate in death.

If envenomation has occurred, signs and symptoms usually start within minutes and may include paresthesia of the lips and tongue. This is usually followed by excessive salivation, trouble with pronunciation (dysarthria), difficulty swallowing (dysphagia), sweating, dizziness and headache. Serious cases may progress to muscular weakness, incoordination, tremors and paralysis. Paralysis may eventually affect respiratory muscles, which can lead to severe hypoxia with cyanosis (blue or purple tissue discoloration due to insufficient oxygen in the blood).


  • These animals are not aggressive, and divers should not fear blue-ringed octopi.

  • If encountered, avoid handling these animals.

  • Due to their small size and lack of skeleton, a blue-ringed octopus den might be a small space only accessible through a tiny crevice, so avoid picking up bottles, cans or mollusk shells in areas the octopi inhabit.

First Aid

Care is supportive. There is no antivenom available. If someone is bitten:
  1. Clean the wound with freshwater, and provide care for a small puncture wound.

  2. Apply the pressure immobilization technique.

    NOTE: TTX is a heat-stable toxin, so the application of heat will not denature the toxin.

  3. Watch for signs and symptoms of progressive paralysis.

    — Be prepared to provide mechanical ventilations with a bag valve mask device or a manually triggered ventilator.

    — Do not wait for signs and symptoms of paralysis. Always seek an evaluation at the nearest emergency department.

    NOTE: The bite site might be painless and still be lethally toxic.

  4. Wound excision is never recommended.