Meet the Deadly Blue-Ringed Octopus

The blue-ringed octopus is an extremely venomous animal known for the bright, iridescent blue rings it displays when threatened. The small octopuses are common in tropical and subtropical coral reefs and tide pools of the Pacific and Indian Oceans, ranging from southern Japan to Australia. Although the blue-ringed octopus bite contains the powerful neurotoxin tetrodotoxin, the animal is docile and unlikely to bite unless handled.

Blue-ringed octopuses belong to the genus Hapalochlaena, which includes four species: H. lunulata, H. fasciata, H. maculosa, and H. nierstrazi.

Physical Characteristics

Like other octopuses, the blue-ringed octopus has a sac-like body and eight tentacles. Ordinarily, a blue-ringed octopus is tan-colored and blends in with its surroundings. The iridescent blue rings only appear when the animal is disturbed or threatened. In addition to up to 25 rings, this type of octopus also has a blue line running through its eyes.

Adults range in size from 12 to 20 cm (5 to 8 in) and weigh from 10 to 100 grams. Females are slightly larger than males, but the size of any octopus varies greatly depending on nutrition, temperature, and available light.

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Octopus Facts: Habitat, Behavior, Diet

By Bob Strauss

Prey and Feeding

The blue-ringed octopus hunts small crabs and shrimp during the day, but it will eat bivalves and small fish if it can catch them. The octopus pounces upon its prey, using its tentacles to pull its catch toward its mouth. Then, its beak pierces the crustacean's exoskeleton and delivers the paralyzing venom. The venom is produced by bacteria in octopus' saliva. It contains tetrodotoxin, histamine, taurine, octopamine, acetylcholine, and dopamine.

Once the prey is immobilized, the octopus uses its beak to tear off chunks of the animal to eat. The saliva also contains enzymes that partially digest flesh, so that the octopus can suck it out of the shell. The blue-ringed octopus is immune to its own venom.

Venom and Bite Treatment

Encounters with this reclusive creature are rare, but people have been bitten after handling or accidentally stepping on a blue-ringed octopus. A bite leaves a tiny mark and may be painless, so it's possible to be unaware of the danger until respiratory distress and paralysis occur. Other symptoms include nausea, blindness, and heart failure, but death (if it occurs) usually results from paralysis of the diaphragm. There is no antivenom for a blue-octopus bite, but tetrodotoxin is metabolized and excreted within a few hours.

First aid treatment consists of applying pressure to the wound to slow the effects of the venom and artificial respiration once the victim stops breathing, which usually occurs within minutes of the bite. If artificial respiration is started immediately and continued until the toxin wears off, most victims recover.

Behavior

During the day, the octopus crawls through coral and across the shallow seafloor, seeking to ambush prey. It swims by expelling water through its siphon in a type of jet propulsion. While juvenile blue-ringed octopuses can produce ink, they lose this defensive ability as they mature. The aposematic warning display deters most predators, but the octopus piles up rocks to block the entrance to its lair as a safeguard. Blue-ringed octopuses are not aggressive.

Reproduction

Blue-ringed octopuses reach sexual maturity when they are less than a year old. A mature male will pounce on any other mature octopus of its own species, whether it's male or female. The male holds the other octopus' mantle and tries to insert a modified arm called a hectocotylus into the female mantle cavity. If the male is successful, he releases spermatophores into the female. If the other octopus is a male or a female that already has sufficient sperm packets, the mounting octopus typically withdraws without a struggle.

In her lifetime, the female lays a single clutch of about 50 eggs. Eggs are laid in autumn, shortly after mating, and incubated under the female's arms for around six months. Females don't eat while incubating eggs. When the eggs hatch, the juvenile octopuses sink to the seafloor to seek prey, while the female dies. The blue-ringed octopus lives one to two years.

Conservation Status

None of the species of blue-ringed octopus have been evaluated with respect to conservation status. They are not listed on the IUCN Red List, nor are they protected. Generally, people don't eat these octopuses, but some are captured for the pet trade.

Sources

• Cheng, Mary W., and Roy L. Caldwell. “Sex Identification and Mating in the Blue-Ringed Octopus, Hapalochlaena Lunulata.” Animal Behaviour, vol. 60, no. 1, Elsevier BV, July 2000, pp. 27–33.
• Lippmann, John, and Stan Bugg. Dan S.e. Asia-Pacific Diving First Aid Manual. Ashburton, Vic: J.L. Publications, 2003.
• Mathger, L. M., et al. “How Does the Blue-Ringed Octopus (Hapalochlaena Lunulata) Flash Its Blue Rings?” Journal of Experimental Biology, vol. 215, no. 21, The Company of Biologists, Oct. 2012, pp. 3752–57.
• Robson, G. C. “LXXIII.—Notes on the Cephalopoda.—VIII. The Genera and Subgenera of Octopodinæ and Bathypolypodinæ.” Annals and Magazine of Natural History, vol. 3, no. 18, Informa UK Limited, June 1929, pp. 607–08.
• Sheumack, D., et al. “Maculotoxin: A Neurotoxin from the Venom Glands of the Octopus Hapalochlaena Maculosa Identified as Tetrodotoxin.” Science, vol. 199, no. 4325, American Association for the Advancement of Science (AAAS), Jan. 1978, pp. 188–89.