Blue-ringed Octopus

Image: Rickard Zerpe

Pretty, titchy, deadly. The Blue-ringed Octopous is like an elegant chocolate laced with cyanide, an ornate thimble full of plutonium or a small child who summons angry bears whenever she's tired.

Blue-ringed Octopuses are a lot more subtle than any bear, though. Unless it's a bear who sneaks around with a syringe of venom. Or one of those bears who leave poisoned porridge around so that people eat it and fall asleep almost immediately, all so they can enjoy the moral outrage of someone sleeping in their bed.

Image: Steve Childs
Tiny, brutally venomous but not horrifically aggressive!

These are the only octopodes in the world definitely known to be venomous. They pull more than their own weight and represent by being incredibly venomous. Each one of these pint-sized tiddlers harbours enough toxin to kill a dozen or two people!

This is not the good kind of pretty where you stop and stare. This is the bad kind where you run away.

Image: Saspotato

There are four, or maybe three species of Blue-ringed Octopus, all belonging to the genus Hapalochlaena. They live in shallow, Indo-Pacific waters, residing in tidal pools and coral reefs from Japan to Australia.

Australia is particularly well-endowed with these venomous pipsqueaks. Dangerous wildlife is, after all, the Australian way.

Image: Angell Williams
Greater Blue-ringed Octopus (H. lunulata). Big rings

The Greater Blue-ringed Octopus (H. lunulata) takes the north. It's most common along Australia's northern coast and is also found up through southeast Asia and as far afield as Sri Lanka. They get their name from having the biggest rings of the lot. They're so big less than 25 of them can fit on the octopus' mantle, with some more along the arms.

Image: Saspotato
Southern Blue-ringed Octopus (H. maculosa). Little rings

The Lesser or Southern Blue-ringed Octopus (H. maculosa) comes from Australia's southern coast. Their rings are so small there can be more than 50 of them on their mantle.

Image: Klaus Stiefel
Blue-lined Octopus (H. fasciata). Lines

The Blue-lined Octopus (H. fasciata) is found on the east coast of Australia. They have rings on their arms but the rest of their body is covered in blue lines, instead.

Finally, the mysterious H. nierstraszi. It was once discovered near India, named, described and never seen again.

Image: Saspotato

They're all of similar size, about 5 cm (2 in) in mantle length. Their arms can more than double that when they stretch them out.

Blue-Ringed Octopuses spend a lot of their time hidden away in rocky crevices. When they're feeling relaxed and happy with life they're just brown or grey or tan coloured. The blue rings are either very faint or not visible at all.

Video: Chan Juitun

Now they can go out on the prowl. Their favourite food is crustaceans like crab and shrimp. The Blue-ringed Octopus pounces on them, cracks a hole in their shell with a tough, octopus beak and injects venom. Prey is soon paralyzed and the struggle over. With such unpleasantness out of the way, our octopus can feed in a peaceful, civilized manner.

Thing is, that venom is a problem for more than just tiny shrimp. Or indeed big, predatory fish. A single bite from these little cuties is lethal to humans! The bite itself is tiny - sometimes people don't even realise it's happened - but if sufficient venom is injected, the poor victim may suffer paralysis and asphyxiation as their lungs stop working. People can die in under ten minutes if they don't get help fast.

Video: BlueWorldTV

The Blue-ringed Octopus advertises the potency of their bite with the selfsame blue rings. When they're agitated or annoyed, the rings brighten up while the surrounding skin darkens for contrast. Soon there's no ignoring them as the rings glow and even pulsate with a malign-yet-pretty power.

The source of this power (the source of the deadly toxin, that is) is, of all things, bacteria. Yup. I guess by now we've all heard of those bacteria that enable all sorts of creatures to glow in the dark via bioluminescence. Well, turns out there are also a whole bunch of bacteria that provide various animals and plants with horrible poisons and toxins. Yay, bacteria.

Image: Saspotato
Blues subdued

The neurotoxin in question is called tetrodotoxin. It's named after one of the main places you find it - fish within the order Tetraodontiformes. Fish like the famous and famously poisonous pufferfish. But it's also found in several other fish, certain starfish, crabs, algae and marine snails. It has even made it onto land, in various salamanders and frogs. And it all comes from these bacteria.

In the case of the Blue-ringed Octopus, the bacteria are packed into their salivary glands. As if spitting wasn't unhygienic enough already. Imagine if they got a cold!

Image: Saspotato

With the killing and eating done, it's time to think of other things. Like almost all other cephalopods, Blue-Ringed Octopuses only live for about a year. Males use a modified tentacle to place packets of sperm in the female's mantle. She settles down in her lair, lays a few dozen eggs and protects them for several weeks until they hatch. She doesn't eat at all during this whole time and dies soon thereafter.

The hatchlings meanwhile drift about in the sea for some time, living the planktonic life. Who knows? Perhaps they're already meeting and greeting some bacterial friends and dribbling deadly saliva all over their podgy chins.