Hapalochlaena fasciata Click to enlarge image
Blue-lined Octopus, Hapalochlaena fasciata Image: Dr Isobel Bennett
© Australian Museum

Fast Facts

  • Classification
    Super Family
  • Size Range
    Body to 5cm, arms to 10cm.

Collectively there are around 10 species known as ‘blue-ringed octopuses’. Several of these are found in Australian waters, with Hapalochlaena fasciata the most common species found around Sydney.


Blue-ringed octopuses usually appear as pale-brown in colour, and are only identifiable by their iridescent blue markings when they are agitated or hunting. Members of the genus Hapalochlaena are united by these blue markings, their small size, strong salivary toxins and egg-carrying by the females.

The Southern Blue-lined Octopus is identified by a pattern of iridescent blue lines on the body and blue-ringed patterns on the arms.


The Southern Blue-lined Octopus is an inshore species found on intertidal rocky reefs and seagrass beds in shallow coastal waters. They can be found from intertidal pools to areas of at least 30m in depth.

A small octopus species, they are often found living in discarded bottles or empty gastropod and bivalve shells.


Subtropical waters off eastern Australia, south of the Great Barrier Reef.

Feeding and diet

They primarily forage at night but can also be found active in rockpools during the day. Like other octopus their diet consists mainly of crustaceans and fish. Blue-ringed octopuses have extremely powerful venom produced by bacteria in their salivary glands which they use to paralyse their prey. They firstly use their beak or radula to create a wound in their prey into which they insert the paralysing saliva.

Other behaviours and adaptations

Blue-ringed Octopuses are thought of as one of the most dangerous animals in the sea. Although their powerful venom has caused some human fatalities, they are very shy and non-aggresive creatures that prefer to hide under ledges and in crevices. Encounters with humans usually result in the octopus quickly darting for cover. It is only when the animal is picked up that it is likely to ‘bite’ and inject its paralysing venom.

Breeding behaviours

Males climb on to the body of the female during mating and are carried around.
Distinct from many other octopus species, the female H. fasciata carries string of large eggs in her web until they hatch. The young when they hatch are well-developed and quickly adopt a benthic lifestyle. From day one the hatchlings already possess the iridescent blue markings which advertise their dangerous nature, as the toxin is passed to the next generation in the eggs.

Danger to humans

The saliva of blue-ringed octopuses contains the powerful nerve toxin, tetrodotoxin. This chemical acts to paralyse prey or predators by blocking nerves from transmitting messages. In humans the toxin acts to cause respiratory failure whilst victims remain fully conscious.Blue-ringed octopuses have been responsible for at least three human fatalities and numerous near-fatalities. In Australia most deaths have actually been attributed to Hapalochlaena maculosa, or the ‘Lesser Blue-Ringed Octopus’ and Hapalochlaena lunulatus.

Blue-ringed octopuses however are timid creatures and will avoid people. It is only when they are handled, harassed or squashed that they have bitten.The bite of Hapalochlaena fasciata may not be felt but within minutes symptoms include numbness of the lips and tongue, difficulty in breathing, followed by complete paralysis of the breathing muscles.

Rapid use of mouth-to-mouth resuscitation has saved the lives of more than 10 documented bite victims. In the event of a suspected bite, seek immediate medical attention.


  • Norman, M., (2000) Cephalopods- A World Guide, ConchBooks, Germany (Hackenheim)
  • Norman, M & A. Reid., (2000) A Guide to Squid, Cuttlefish and Octopuses of Australasia, CSIRO Publishing, Victoria (Collingwood)