Blue-ringed octopus: Beautiful yet deadly, capable of killing 26 people in one minute

The blue-ringed octopus may look beautiful and small, about the size of a golf ball or even a penny, but it's also very dangerous. Its bright yellow skin has small blue rings that get brighter when it's scared or stressed. You can find these octopuses in the warm, shallow waters of the Indian Ocean, Pacific Ocean, from Australia to Japan.

Despite their charming appearance, these octopuses are venomous. The venom of this octopus could kill 26 adults in just a few minutes. They are fascinating creatures but need to be handled with caution due to their deadly venom.

Marine zoologist Peter Morse from James Cook University in North Queensland, Australia, specializes in studying blue-ringed octopuses, particularly their mating behaviors. According to Morse, one key difference between the two species of blue-ringed octopuses lies in their reproduction methods.

The greater blue-ringed octopus, which tends to live longer and grow slightly larger, goes through a planktonic larval phase. This means they begin their lives as plankton before developing into the octopuses we recognize. This larval phase helps them spread over longer distances, expanding their range and increasing their population numbers. In contrast, the southern blue-ringed octopus hatches as miniature adults, skipping the larval phase.

What is a blue-ringed octopus and where do you find it?

Blue-ringed octopuses are small but very venomous sea creatures. They live in the Pacific and Indian oceans, mainly around coral reefs, rocky areas, tide pools, and seagrass beds. These octopuses come out at night to hunt for crustaceans and sometimes small fish.

They have distinctive blue rings on their bodies and arms, which act as a warning to predators. Unlike some animals that always display bright colors, blue-ringed octopuses only show their blue rings when they feel threatened. They can change color quickly using special cells called chromatophores and iridophores, making their blue rings stand out against a yellow or cream-colored background.

There are about 10 species of blue-ringed octopuses, but only four have scientific names. They vary in size and coloration, with the largest reaching about 22 centimeters long. One species, the blue-lined octopus, has blue lines on its mantle and blue rings on its arms. Another species, Hapalochlaena nierstraszi, is rare and not well studied.

Researchers have officially seen the fourth species, Hapalochlaena nierstraszi, only twice: once in the waters near the Andaman Islands in 1938 and again in 2013 when a trawling net near Chennai in southeast India caught one. We don't know much about this species, although the specimen found in 1938 had a mantle length of 16 centimeters.

What do they eat?

Despite their small size, blue-ringed octopuses are skilled hunters. They hunt and catch crustaceans, small mollusks, and even chase after small fish.

When hunting, the blue-ringed octopus ambushes its prey by using its arms to draw it towards its beak. It then injects venom through the prey's shell to paralyze and kill it. Normally, these octopuses have yellow skin with dark brown rings, but they can change color when threatened. This color change is caused by special ink-filled sacs called chromatophores under their skin. When they feel danger, these sacs stretch, making their rings turn bright neon blue. After the threat passes, the sacs contract, and their color returns to normal.

Blue-ringed octopus venom

The octopus's colorful displays serve as a serious warning because their venom can be deadly.

Inside the salivary glands of blue-ringed octopuses live symbiotic bacteria that produce tetrodotoxin (TTX). This neurotoxin is incredibly potent, blocking nerve signals and leading to muscle paralysis, which can be fatal. TTX is more than 1,000 times stronger than cyanide and is also found in various animals like pufferfish, which store it in their organs.

Blue-ringed octopuses carry a potent neurotoxin called tetrodotoxin, similar to the venom found in pufferfish. While their bites can be highly toxic, blue-ringed octopuses typically avoid biting humans unless provoked.

If someone is bitten, the effects of the venom can last between 12 to 48 hours, depending on factors like the person's size and the amount of venom injected. The venom blocks nerve signals in the body, leading to "flaccid paralysis," which affects smooth muscles such as the diaphragm, causing breathing difficulties within minutes of the bite.

"Because they're nocturnal and they're very shy and they give plenty of warning as well, you really would have to be very stubborn to get bitten," Morse says. "The venom is very potent and there isn't an antivenom. But the venom does wear off, so if the person could get life-saving techniques during that time, they could be OK."

How do they hunt?

Blue-ringed octopuses are skilled ambush hunters, employing a sneaky approach to catch their prey. Like many cephalopods, they excel at ambush hunting rather than chasing prey actively. Known for their intelligence, these creatures prefer to remain motionless and wait for prey to come within striking distance.

"When it comes to hunting, blue-ringed octopuses play it safe despite their venomous bite, especially considering the potential risks posed by larger prey like crabs," says marine zoologist Peter Morse from James Cook University.

One intriguing aspect of blue-ringed octopuses, according to Morse, is how they acquire and use their venom. Unlike other venomous animals, blue-ringed octopuses don't produce venom themselves. Instead, it's synthesized by bacteria in their salivary glands. However, the origins of these bacteria and how the venom is transmitted from one generation to the next remain a mystery.

"We still don't fully understand whether captive blue-ringed octopuses need specific exposure or diet to maintain their venom," Morse adds, highlighting ongoing research gaps in their venom production and transmission mechanisms.

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