Picture an octopus that could be deadly to humans. You’re probably thinking of a large creature, and not one that is the size of your palm.

But indeed, that’s the blue-ringed octopus, one of several shallow-dwelling species harboring a neurotoxin in its saliva with the capability of paralyzing muscles – an effect that could, if left unaddressed, lead to fatal consequences.

There might be around 10 species of these tiny octopuses in the Hapalochlaena genus, but the more well-known examples include the lesser blue-ringed octopus (H. maculosa) and the greater blue-ringed octopus (H. lunulata).

In the same way a poisonous dart frog has a vividly colored body, blue-ringed octopuses harbor iridescent blue rings to warn of their poisonous nature. These spots stand out against dark brown backgrounds, mottling their typically beige or gray bodies.

Don’t be fooled by the beauty of these rings: These octopuses are among the deadliest of cephalopods, and there’s plenty that researchers still need to learn about them.

The Life of a Blue-Ringed Octopus

Different species of blue-ringed octopuses occupy different swathes of the sea, but most of these octopuses can be found in the waters of the Pacific and Indian Oceans. Within those waters, they prefer living in shallow areas, between zero and 50 meters in depth, and can find their homes within reefs or seagrass beds.

The greater blue-ringed octopus is native to the tropical western Pacific, including northern Australia, Papua New Guinea, Indonesia, the Philippines, and the Solomon Islands. It can even be found in the waters of Japan. Meanwhile, the lesser blue-ringed octopus lives along the coast of southwestern Australia to eastern Victoria, as well as Tasmania.

Blue-ringed octopuses typically have short lifespans, with most members of the species living for less than two years and reaching sexual maturity after four months.

According to the MarineBio Conservation Society, after mating, female octopuses can lay batches of up to a hundred eggs, which they then guard for about 50 days until they hatch, after which the mother dies. If blue-ringed octopuses are small as adults, then these juveniles are even smaller, about the size of a pea.

They are nocturnal foragers, enjoying a diet of small crustaceans – including crabs and shrimp – as well as small fishes. To hunt, they utilize the deadly neurotoxin contained in their salivary glands to paralyze their prey. Once the prey is effectively subdued, the octopus uses its sharp beak to puncture the hard exterior of its victims to consume their softer flesh.

Read More: Are Octopus Smart? A Look Inside the Brain of an Octopus

A Deadly Venom

But what precisely is contained in its venom? The neurotoxin in blue-ringed octopus saliva is called tetrodotoxin (TTX), and it’s produced by bacteria lingering in their salivary glands – though TTX can be found in other body parts such as octopus arms and abdomens.

This is an extremely strong toxin, over 1,000 times stronger than even cyanide, for which there is no antidote. It reduces the movement of sodium throughout membrane channels to block nerve functions.

If a person is exposed to enough TTX, they’ll rapidly experience a progression of paralysis. Their muscles will weaken, and they might experience additional symptoms like nausea and vomiting or vision loss. Where the potential deadliness kicks in is if TTX begins to affect the diaphragm, the muscle that controls our breathing. That may lead to respiratory failure, and if left untreated, even death.

Because there’s no antidote to TTX, the necessary medical treatment includes artificial respiration and breathing support, until the poison leaves the system. Humans have in fact died from blue-ringed octopus bites before, with two fatalities happening in Australia during the 1950s and 1960s.

How to Know if Blue-Ringed Octopus Will Bite

Despite the danger they can pose to humans, potential death by octopus is nothing that keeping a little distance and wariness can’t prevent. Blue-ringed octopus don’t bite or release their poisons unless they feel agitated or threatened – and if they do bite, it’s often painless and unnoticeable. This is why you should never try picking up a blue ringed octopus if you find one in the wild.

Blue-ringed octopuses flash their rings in warning, turning them an iridescent blue to signal their agitation. They can do this by using specialized cells to give their rings that deadly sheen.

Read More: These Octopuses Throw Objects, Sometimes At Each Other

Is the Blue-Ringed Octopus Endangered?

There’s still much to understand regarding the toxicology of blue-ringed octopuses, for example, or how many species are out there. Along with the question of whether blue-ringed octopuses are a threatened species.

The International Union for Conservation of Nature (IUCN) Redlist last evaluated the blue-ringed octopus as a species of least concern in 2014. This means there are no conservation measures in place for the species and it does not qualify as endangered.

While scientists aren’t sure yet what the true population trends of blue-ringed octopuses are looking like, the effects of climate change on the coral reefs where they find their homes, for example, have the potential to pose a threat.

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