Blue-Ring Octopuses and Venomous Octopuses

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blue-ringed octopus
All octopuses produce venom, but only a few can cause death to humans. Three or four species of closely-related blue ringed octopus rank with some cone shells for the title of the world's most poisonous mollusks — and for that matter the most poisonous creature in the sea. Residing in the waters off of Australia, Indonesia, and parts of Southeast Asia, these species of octopus carry a toxin capable of killing a person in minutes, with some carrying enough toxin to kill 10 people. Fortunately the octopus are not aggressive, and bite only when taken out of the water and provoked.

Blue-ringed octopuses are the most well-known venomous octopuses. The name Blue-ringed Octopus is actually given to a group of octopods consisting of four different species: 1) the greater blue-ringed octopus (Hapalochlaena lunulata), 2) the southern blue-ringed octopus (Blue-ringed octopus), 3) the blue-lined octopus (Hapalochlaena fasciata) and 4) the common blue-ringed octopus (Hapalochlaena nierstraszi). These octopuses are small enough to fit in the palm of your hand. The greater blue-ringed octopus has larger rings than the blue-ringed octopus and is most commonly found on Australia's northern coast. Theblue-lined octopus, has lines instead of rings on its body and is found only in New South Wales. [Source: Ashleigh MacConnell, Animal Diversity Web (ADW); [ Harry Baker, Live Science, March 27, 2023]

The toxin found in blue-ringed octopuses and pufferfish consumed by the Japanese — tetrodoxotin — is a powerful nerve agent that causes rapid onset of paralysis and breathing difficulty. Powerful toxins (lethal dose): 1) anthrax (0.0002); 2) geographic cone shell (0.004); 3) textrodoxotine in the blue ring octopus and puffer fish (0.008); 4) inland taipan snake (0.025); 5) eastern brown snake (0.036); 6) Dubois’s sea snake (0.044); 7) coastal taipan snake (0.105); 8) beaked sea snake (0.113); 9) western tiger snake (0.194); 10) mainland tiger snake (0.214); 11) common death adder (0.500). Lethal doses is defined as the amount in milligrams needed to kill 50 percent of the animals tested.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal

Blue-Ringed Octopus

blue-ringed octopus

Blue-ringed octopuses (Scientific name: Hapalochlaena maculosa, are diminutive creatures that get their names from the blue markings the animals display when they are aroused or disturbed. Adults are generally 15 centimeters or less in length. They wards off predators with tetrodotoxotin and catch prey such as crabs with a second, less-potent toxin. The arousal display includes a wide array of indigo rings and lines along their mantle and arms.

Blue-ringed octopuses are native to Australia, the Indian Ocean and Pacific Ocean. They are most commonly seen in rocky, shallow pools of water or in shallow corals or reefs and can also found under rocks in sandy or muddy stretches of bottom where alga is plentiful. They are particularly common after storms when they search around for crabs and bivalves. [Source: Ashleigh MacConnell, Animal Diversity Web (ADW) /=]

Blue-ringed octopuses have striking colors and lack an ink sac and therefore are desired by aquarium enthusiasts. The trade of these octopus is frowned by toxicologists who feel that the people buying and selling them are uninformed of about the danger they pose. This species also is used for its venom. Australia has a venom industry, whose main purpose is to supply toxins for medical research. /=\

Blue-ringed octopus. have not been evaluated for International Union for Conservation of Nature (IUCN) Red List. An issue has arisen related to publicity about the toxicity of their venom. People sometimes kill octopuses they encounter in shallow tidal pools. /=\

Blue-Ringed Octopus Toxin

range of the blue-ringed octopus

Blue-ringed octopus saliva contains tetrodotoxin, and people have been bitten often experience symptoms such as vomiting, paralysis and spasms. Live Science reported: Tetrodotoxin stops nerves from signaling to muscles by blocking sodium ion channels. This causes rapid weakening and paralysis of muscles, including those of the respiratory tract, which can lead to respiratory arrest and death. The effects of tetrodotoxin can occur rapidly or have a delayed onset, so death can occur anywhere between 20 minutes and 24 hours after the toxin enters the body, according to the Centers for Disease Control and Prevention (CDC). [Source: Harry Baker, Live Science, March 27, 2023]

Blue-ringed octopuses do not create tetrodotoxin themselves. Instead, the toxin is produced by symbiotic bacteria that live in their salivary glands, according to the Australian Institute of Marine Science. Tetrodotoxin is found throughout the octopus's tissues, not just in specific venom glands, which makes them some of the few animals that are both poisonous and venomous. It also means that a person can receive a lethal dose if one of these octopuses touches their skin.

There is no known antidote for tetrodotoxin. All health care practitioners can do is provide supportive care or use a ventilator if patients are unable to breathe, according to the CDC. Medical and psychological researchers are interested in tetrodotoxin neurotoxin found in its purported aphrodisiac effects and its ability to block voltage-sodium channels so action potential in neurons is inhibited or reduced. Blue-ringed octopuses aren't the only animals that contain tetrodotoxin; it can be found in some newts, frogs and puffer fish.

Blue-Ringed Octopus Characteristics and Behavior

Blue-ringed octopuses are small octopuses with an average weight of 26 grams (0.92 ounces). They range in size from 4 millimeters at birth to up to 20 centimeters (8 inches), including tentacles, when they are adults. adulthood. These octopuses are are dark brown, dark yellow or tan-yellow in color when they are not aroused. Their most distinguishing characteristic are the iridescent blue rings in their eye spots. Their rings reportedly "glow" when they are aggravated. [Source: Ashleigh MacConnell, Animal Diversity Web (ADW) /=]

blue-lined octopus

According to Animal Diversity Web: The blue-ringed octopus is a nonaggressive octopus and in general exhibits the typical behaviors of octopuses — anachoresis, burrowing, and aposematism. Anachoresis is living in crevices and holes. Burrowing is where an octopus establishes a den or refuge for itself by excavation of sand, mud, gravel, and coral rubble. This can often pose a problem in an aquarium environment, where underground filters are common. Aposematism, or advertising toxicity, in this species includes the "glowing" of the iridescent blue-ringeds, and often a yellow and black striping of the body. In general, not much is known of use of these displays in this particular species. /=\

Blue-ringed octopuses spend most of their time hiding in crevices. They can change shape easily, which helps them to squeeze into crevices much smaller than themselves. This, along with with their camouflage and habit of piling up rocks outside the entrances of their hiding places helps keep them out of reach of predators. If blue-ringed octopus are provoked, they quickly change color, becoming bright yellow with each of the 50–60 rings flashing bright iridescent blue within a third of a second. The flashing rings on the octopuses' bodies warn predators of their toxicity and caused by tiny color-changing organs called chromatophores, which are dotted across the animals' skin. Similar to other Octopoda, the blue-ringed octopus swims by expelling water from a funnel in a form of jet propulsion. [Source: Wikipedia, Live Science]

Blue-Ringed Octopus Reproduction and Feeding

According to Animal Diversity Web: The female will initiate reproduction by specific coloring and posturing. The male will then approach her to begin courtship. Courtship consists of "love play" and caressing. The male will then use the hectocotylus, a modified arm consisting of a groove between the suckers and ending in a spoonlike tip, to deposit the sperm in the female's oviduct, which is located under the mantle. [Source: Ashleigh MacConnell, Animal Diversity Web (ADW) /=]

Shortly thereafter, the female will begin to lay her eggs and the brooding period will begin. Characteristic brooding of this species is for the female to carry the eggs in its arms. She will guard them for a period of fifty days, at which point they will hatch into planktonic "paralarva". Initially at birth, the octopus will be only 4 millimeters long. This stage of the life cycle, the young will float to the top and join the plankton for about a month. At the end of this time period they will once again return to the bottom to resume their normal life.

spotting pattern on a blue-ringed octopus

At one week of age, the blue-ringed octopus will begin to eat crab pieces. As the octopus matures, it will begin to eat live crabs and bivalve mollusks. The octopus will either entice its prey into its vicinity and inject a poison into the water that will paralyze it or will inject the poison into its prey directly. It is also believed that the octopus will capture prey, forming an airtight pouch around it, and inserting the poison into the pouch, cause the prey to take the poison in through its respiratory system. The poison is a neurotoxin which causes paralysis, which is particularly fatal if the poison affects either the heart or repiratory system. To date there is no antitoxin. Generally though, humans are not considered prey to this creature and a bite from one seems to be more of a defensive response than anything else. /=\

Greater Blue-Ringed Octopus

Greater blue-ringed octopuses(Scientific name: Hapalochlaena lunulata) are found along the coasts of Northern Australia and farther north in the tropic western Pacific Ocean in shallow coral and rock pools. They are often observed after storms, digging around for crabs. Otherwise they tend to hide in crevices amongst rocks, inside seashells, and discarded bottles and cans. Their soft-bodies are vulnerable to attacks from predators. These creatures are also have valued as expensive pets. A greater blue-ringed octopus individual was sold for $4000 at an auction in Sydney, Australia a few years ago. [Source: Kelly Ray, Animal Diversity Web (ADW) /=]

Greater blue-ringed octopuses are distinguished from blue-ringed octopuses by their larger rings. Greater blue-ringed octopuses weigh between 0 to 100 grams (0.35 to 3.52 ounces) and reach a length of around 20 centimeters (8 inches), including tentacles, but under normal circumstances, appears much smaller than this. According to Animal Diversity Web: The Greater blue-ringed octopus is dark brown to dark yellow in color, but with brilliant blue-ringed thought to be warning coloration that "glow" when it is angry. The reason the rings are blue is thought to be that the visual range of the octopus is most sensitive in the blue part of the spectrum. At the small beak at the junction of its eight arms rather than manufacturing ink, Greater blue-ringed octopus makes poison like the tetrodotoxin found in poisonous puffer fishes. Bacteria in their salivary glands produce it. The venom, contained in its saliva and designed to subdue or kill its prey is particularly lethal to human beings. /=\

different spotting pattern on a blue-ringed octopus

In the greater blue-ringed octopus rings contain multi-layer light reflectors called iridophores that are arranged to reflect blue–green light in a wide viewing direction. Beneath and around each ring there are dark pigmented chromatophores which can be expanded within 1 second to enhance the contrast of the rings. There are no chromatophores above the ring, which is unusual for cephalopods as they typically use chromatophores to cover or spectrally modify iridescence. The fast flashes of the blue rings are achieved by using muscles which are under neural control. Under normal circumstances, each ring is hidden by contraction of muscles above the iridophores. When these relax and muscles outside the ring contract, the iridescence is exposed thereby revealing the blue color. [Source: Wikipedia]

There has been some speculation that these color changes may be a form of communication, especially the pulsating blue of the excited state. It may be both a warning to potential predators and as a means of communicating with other greater blue-ringed octopuses. Greater blue-ringed octopus diminish their colors while retreating and escaping. and flash their characteristic electric blue ring markings when agitated. /=\

Greater Blue-Ringed Octopus Feeding and Reproduction

Greater blue-ringed octopus feed primarily on fish, crabs, mollusks and other small marine animals. According to Animal Diversity Web: It hunts every thing that it is able to overpower. It ambushes prey from the background, often luring its victim by wiggling the tip of an arm like a worm. When hunting crabs, glides near and pounces on its prey, trapping it in its arms and dragging it towards its powerful beak-like jaws. Once it has bitten its prey, the octopus injects it with poisonous saliva to kill it. A greater blue-ringed octopus can crack prey open with its jaws or disarticulate it with the tips of its arms, removing the edible parts. [Source: Kelly Ray, Animal Diversity Web (ADW) /=]

A male interested in mating approaches a female just close enough to stretch out a modified arm, the hectocotylus, and caress the female. This arm has a deep groove between the two rows of suckers and ends in a spoon-like tip. After a period of caressing the female with the tip of the hectocotylus, the male inserts its arm under the mantle of the female, and the spermatophores then travel down the groove on the hectocotylus to the female's oviduct.

Soon after mating, the female begins to lay 60-100 eggs, which she carries in a cluster underneath her tentacles. She then guards them for the next 50 days. The eggs hatch into planktonic paralarvae and spend their first weeks as ocean plankton, drifting at the surface. After gaining weight, they drop to the bottom. Because she stops eating while brooding her eggs, the mother dies almost as soon as they hatch. The young are ready to reproduce around four months after hatching.

People Bitten and Killed by Blue-Ring Octopuses

well-camouflaged blue-ringed octopus off New South Wales

Blue-ringed octopuses are considered one of the most dangerous animals in the sea because of the high toxicity of their venom. Despite this there has never yet been a report of an octopus attacking a human. In general this species is nonaggressive and will only bite if picked up or stepped on. The bite of the blue-ringed octopus is not painful. There have been reports of people handling one and becoming very sick because they did not realize they had been bitten until the symptons of envenomation began to occur.

The poison from blue-ringed octopuses is especially dangerous to young children. There is no antivenom for it. Of the handful of human fatalities,all have involved the animal being picked up. Five minutes or after a bite the victim may complain of dizziness and increasing difficulty in breathing. The powerful venom acts on the victim's voluntary and voluntary muscles, inhibiting or paralyzing the muscles required for body movement and breathing. Artificial respiration is necessary to maintain life. The poison gradually wears off after 24 hrs, apparently leaving no side effects. [Source: Kelly Ray, Animal Diversity Web (ADW)]

Despite being so toxic, blue-ringed octopuses have caused only three confirmed deaths, according to WebMD. One man bitten on the toe by a blue-ringed octopus at Shoalhaven Beach in New South Wales, Australia was dead within five minutes. In June 2004, two people were killed and 85 other were hospitalized after eating poisonous octopuses in Vietnam. The trader said he sold more than 20 kilograms of blue ring octopus at a market in Nihn Thuan Province, 200 kilometers north of Saigon, said he sold the octopuses many times before but didn’t know the blue ring octopus was poisonous. Many of those admitted to the hospital suffered from diarrhea and vomiting. Seventy-two, including 28 children, remained hospitalized for a period of time.

According to Live Science: While blue-ringed octopuses rarely kill people, there have been plenty of close calls.In 2006, a 4-year-old boy was almost killed after being bitten by an octopus he picked up in a rock pool on a beach in Queensland. The boy vomited several times before developing blurred vision and then losing control of most of his muscles, according to a case report published in the journal Clinical Toxicology. After spending 17 hours on a ventilator, he eventually made a full recovery. And in March 2021, a woman was heavily criticized online after sharing a video of herself holding a blue-ringed octopus in Bali, although she did not know it was highly toxic at the time and escaped unscathed, according to Insider. [Source: Harry Baker, Live Science, March 27, 2023]

In March 2023, a woman was bitten twice on her abdomen by an unknown species of blue-ringed octopus at a beach near Sydney in New South Wales. She had collected a small shell while swimming, and when she picked it up to look at it, the tiny cephalopod fell out and landed on her stomach, the New South Wales Ambulance service wrote on Facebook. The woman experienced some abdominal pain and was treated with cold compresses before being taken to the hospital to be monitored for more symptoms, according to NSW Ambulance. It is unclear why the woman escaped relatively unharmed.

Blue-Ringed Octopus Spotted in Japan

In May 2012, the Yomiuri Shimbun reported: “Poisonous blue-ringed octopuses, which inhabit mainly tropical and semitropical zones in the Western Pacific, have been recently found in increasing numbers in the Kumano-nada area off the coast of southern Mie Prefecture.It is rare for blue-ringed octopuses, which carry tetrodotoxin, the same deadly poison present in fugu blowfish, to be found in the area during February and March when the weather is cold. [Source: Yomiuri Shimbun, May 30, 2012]

“An expert said, "Their habitat might have expanded north due to the rise in sea temperatures caused by global warming." An official of the Mie Prefecture Fisheries Research Institute in Shima found a blue-ringed octopus on the seafloor at a depth of 10 meters off the coast of Taiki, Mie Prefecture, on Feb. 16.Another was caught after being found on rocks about seven meters under water off Shima on March 7. Both octopuses were adults about 10 centimeters in length, the institute said.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated April 2023

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