Blue-Ringed Octopus

Blue-ringed octopuses are small, venomous octopuses that live in tropical tide pools from southern Japan to the coastal reefs of Australia and the western Indo-Pacific. These small octopuses 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 note 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.

There are three species of blue-ringed octopuses:

  • Greater blue-ringed octopus (Hapalochlaena lunulata)
  • Southern (or lesser) blue-ringed octopus (Hapalochlaena maculosa)
  • Blue-lined octopus (Hapalochlaena fasciata)

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

Mechanism of Injury

Like all cephalopods, octopuses have strong beaks similar to those of parrots and parakeets. All octopuses 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 — an amount that could fit 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 by 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, loss of coordination, 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).

First Stage: Initial Presentation

  • Prickling and tingling (paresthesia) of the lips and tongue, followed by facial and extremity tingling and numbness
  • Headache, sensations of lightness or floating
  • Profuse sweating (diaphoresis)
  • Dizziness
  • Salivation (ptyalism)
  • Nausea, vomiting (emesis), diarrhea, abdominal (epigastric) pain
  • Difficulty moving (motor dysfunction)
  • Weakness (malaise)
  • Speech difficulties

Second Stage

  • Progressive paralysis
    • First in the extremities
    • Then in the rest of the body
    • Finally in the respiratory muscles; causing
      • difficulty breathing or shortness of breath (dyspnea)
      • abnormal heart rhythms (cardiac dysrhythmias or arrhythmia)
      • abnormally low blood pressure (hypotension)
      • fixed and dilated pupils (mydriasis)
      • coma, seizures, respiratory arrest, and death


  • These animals are not aggressive, and divers should not fear blue-ringed octopuses.
  • If encountered, remain at arm’s length and 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 these octopuses are known to inhabit.

First Aid

Care is supportive. There is no antivenom available.

  • Clean the bite site with freshwater, and provide care for a small puncture wound.
  • Apply a pressure immobilization wrap. TTX is a heat-stable toxin, which means application of heat will not alter the it.
  • Watch for signs and symptoms of descending paralysis. Be prepared to provide mechanical ventilations with a bag valve mask or manually triggered ventilator. Seek professional medical care (do not wait for signs and symptoms of paralysis). Evaluation and observation should be sought at the nearest emergency department or medical facility. Beware: The bite site might be painless and still be lethally toxic.
  • Wound excision is never recommended.

Implications in Diving

For the Diver

  • Administer first aid as described above.
  • Although the bite might be almost imperceptible and painless, immediately seek professional medical evaluation. Never underestimate a bite from a blue-ringed octopus. The toxin from these animals can kill a human in as little as 20 minutes.

For the Diver Operator

  • As the leader of the expedition, you have a duty of care if the injured person was hurt during your trip.
  • Provide first aid treatment as descried above.
    • There may be many folkloric first aid treatments; use common sense, and refrain from attempting any scientifically unsound solutions. Remember you might be liable.
  • Take your customer to the closest medical facility. Never underestimate a bite from a blue-ringed octopus. The toxin from these animals can kill a human in as little as 20 minutes.
  • Don’t worry about finding a doctor with dive medicine experience; these envenomations are not the purview of a dive medicine expert but rather an emergency medicine specialist or toxicologist.

For the Physician

  • See first aid treatment described above.
  • Definitive treatment is symptomatic and supportive. All fatalities reported have been due to respiratory depression.
  • TTX poisoning may either have rapid onset (10 to 45 minutes) or delayed onset (generally within 3 to 6 hours but rarely longer).
    • Death may occur as early as 20 minutes or as late as 24 hours after exposure; it usually occurs within the first 4 to 8 hours.
    • Patients who live through the acute intoxication in the first 24 hours usually recover without residual deficits. Symptoms may last for several days, and recovery takes days.

For additional information about marine life injuries, check out the Hazardous Marine Life Medical Reference Book.