By Mike Waddington

The ocean is home to some of the strangest animals on Earth, (excluding the Platypus) and many of them have evolved strange and powerful chemicals to aid their hunting or help them defend themselves from predation.

What is the Difference Between Venomous and Poisonous?

I remember watching a BBC documentary about Indonesia where the narrator (luckily not the great David Attenborough) described a sea snake as being a poisonous species, which is 100% incorrect, and made worse by the fact that in the previous scene they had been described as venomous.

There is a major difference between the two.

An animal that is poisonous contains toxins (sometimes incredibly powerful), stored within its flesh or organs, or a mucus surrounding it. These animals have no way to deliver those toxins, however, ingesting those animals could be fatal. Pufferfish and poison dart frogs are some of the most famous examples of poisonous animals. Poison is a powerful defence mechanism as most creatures have learnt that eating that species would result in death.

An animal that is venomous has a way of delivering their toxin, through a bite, a sting, or spines. Many of these species are not poisonous themselves, and a number of venomous species are eaten throughout the world, such as coral snakes in China, and Lionfish in the Caribbean.

Six of the Most Venomous Animals in the Ocean

Here we have compiled a list of the some of the most venomous creatures in the sea. Fortunately for us, none of these animals are aggressive, and incidents only happen by accidentally touching the animal, or a human provoking it into defending itself.

Please note that this list is not in any particular order of toxicity, however saying that, we did save the best (or worst) for last.



Textile Cone Snails

You may have been told that you should never take shells because they are potential hermit crab homes and will eventually break down to produce sand, but did you know that taking a shell from the reef could kill you in less than five minutes?

There are over 800 known species of cone snail found throughout all the world’s tropical and subtropical seas, and all are venomous to some extent. They are sophisticated predatory gastropods that use their venom to immobilize and kill their prey before eating it, and they will use this same venom as a defence mechanism if somebody tries to touch one.

They inject their venom via launching their harpoon like modified radular tooth, which looks like a very fine transparent needle. This tooth is so fine and fired at such a velocity that it can even penetrate wetsuit neoprene, however you are unlikely to feel it.

One of the most dangerous is the textile cone snail, which due to its beautiful shell has been linked to a number of deaths by unsuspecting divers or snorkelers attempting to remove them from the reef. Once stung, the victim might feel localised numbness or tingling. This is because one of the components of the venom is an extremely powerful analgesic (painkiller) which is said to be stronger than morphine. Often the victim doesn’t feel this, and it is quickly followed by muscle paralysis and respiratory failure.

Because of the venom’s analgesic properties, it has been well studied by the pharmaceutical industry, and there are drugs available on the market that are used to treat Parkinson’s and epilepsy that are based on the cone snails venom.

They only fire their harpoons for hunting and defence, so you are safe as long as you remember to never pick up a shell while underwater.



Banded Sea Krait

For ophidiophobes (someone who is afraid of snakes) I’m sorry to inform you that not even the ocean is snake-free. There are 69 species of coral snake, and every single one of them is venomous.

The banded sea krait is probably the most well-known species, one of the most common, and one of the most venomous. Their venom is a powerful neurotoxic protein that causes symptoms such as headache, thirst, sweating and vomiting, followed by more serious symptoms like hypertension and convulsions.

Luckily for us, banded sea kraits (and all other species of coral snake) are very docile and will only ever bite a human if they feel extremely threatened. Even then, you are most likely not in any danger. It takes quite a long time for coral snakes to produce their venom, so they rarely inject it for defensive bites, instead saving it for taking down prey. The vast majority of human bites occur to fishermen when the snake has become caught on a line or in a net, and very rarely have these bites been envenomed. Incidents involving coral snakes are extremely rare, which is impressive when you consider the fact that they come to shore to lay eggs and therefore are frequently in contact with humans.

Only one species of sea snake –the yellow-bellied sea snake- is found world-wide, and the other 68 are localised to the Indo-Pacific, so if you are scared a snakes, your best bet would be to stick to the Caribbean or only go for cold water diving.



Flower Urchin

Sea urchins are already high up on the ‘what to avoid touching’ list of most divers and snorkelers, but mostly because being stung by one is a bit painful. On the other hand, a flower urchin sting is a very different experience.

Found only in the Indo-Pacific, flower urchins envenom their victims differently to other species of sea urchin. Rather than injecting via their spines, the venom is delivered through the tips of their flower shaped pedicellariae (similar to claws) which snap shut if disturbed.

Once envenomed, the victim will feel immediate pain similar to that of a jellyfish, and this pain sensation will move very quickly towards the heart. Other symptoms will include paralysis, muscle relaxation, respiratory problems, and unconsciousness. Although stings are painful and very unpleasant, deaths are extremely rare. Most deaths attributed to flower urchins are due to drowning from the paralysing compound of the venom rather than the venom itself.

Just like any other urchin, flower urchins can be found in great numbers on shallow sea grass meadows, so if you want to avoid getting stung, stay off the grass!



Stonefish

The world’s most venomous fish needs no introduction.

Stonefish are members of the order Scorpaeniformes, which includes other well-known venomous species such as scorpionfish and lionfish. The name stonefish comes from their amazing camouflage, often looking more like a rock than a fish.

Native to the Indo-Pacific, these masters of camouflage are benthic ambush predators, which means they hide on the bottom and wait for their prey to come to them. They can be sitting on top of the reef, buried in the sand with only their face showing, or even sitting in very shallow waters and in sea grass meadows.

Their powerful sting comes their 13 dorsal spines, each one equipped with two venom sacks and stiff enough to penetrate boot soles. Once stung, the victim will feel severe pain, shock, and localised tissue death. Luckily, the venom is treatable. Immediate first aid involves submerging the wound in hot water as this will destroy the venom, and anti-venom is available for severe cases.

If you are looking for a reason to improve your buoyancy control and stay off the bottom, avoiding stonefish is definitely a good one.



Blue-Ringed Octopus

Most people don’t know this, but all species of octopus are venomous, however not all venom is created equally. Originally brought to the limelight in the 1983 Bond movie, Octopussy, the blue-ringed octopus is well known as one of the most venomous animals on Earth.

The blue-ringed octopus is not an individual species, but a genus known as Hapalochlaena that comprises of four confirmed species, and a further six potential species that are still being researched.

Although blue-ringed octopuses are small –typically weighting less than 30 grams – a single specimen has enough venom to kill up to 26 adult humans in only a few minutes. The key ingredient of their venom is tetrodotoxin, which is best known as the fatal ingredient in pufferfish. Upon being bitten, you can expect symptoms such as nausea, heart failure and total body paralysis. If left untreated, death can occur in minutes due to suffocation as the diaphragm will also become paralysed. There is no anti-venom available, however the venom does wear off over time, so as long as artificial respiration is provided in time, the victim should make a full recovery.

This may sound terrifying, but it is important to note that blue-ringed octopus are incredibly docile creatures, and bites are extremely rare. While most octopus use their colour changing chromatophores to blend in with their surroundings, blue-ringed octopus use theirs to stick out. Normally they are a dull grey colour, blending in with any rock, but if they feel like a threat is present, they will change their body to yellow and flash up to 60 bright blue rings as a warning of their venomous bite. They also flash their blue rings while swimming and moving about the reef, because this is when they are most vulnerable to being attacked.

Their docile nature, beautiful colouration, tiny size and fatal potential makes them a hit amongst divers and underwater photographers. They are found throughout much of South East Asia and Northern Australia, and usually live in shallow rocky areas.



Sea Wasp

Out of all the creatures on this list, this is the only one I would actively avoid and choose not to dive with. We obviously had to include a jellyfish on this list, but with so many potentially fatal choices, which one do we choose?

We opted to go with the Chironex fleckeri, or more commonly “sea wasp”. This species is an extremely venomous animal that is a member or the jellyfish class Cubozoa or “box-jellyfish” which are named so due to their square shape.

Found from Northern Australia to Vietnam, and west to the Gulf of Thailand, the sea wasp holds the title of the world’s most venomous animal, and a single tentacle could have enough venom to kill up to 60 adult humans in less than five minutes. Just like any other jellyfish, they drift aimlessly throughout the oceans going with the current, and if you happen to be in the path of its three metre tentacles, you are in for a nasty surprise.

The victim will feel an immediate burning sensation which is likened to being branded by a red hot iron. This pain is strong enough the cause cardiac arrest within minutes of being stung. Those most at risk to cardiac arrest are young children and the elderly, however, a number of the recorded deaths are from swimmers who get stung and cannot get back to shore due to the intense pain. Luckily most cases of sea wasp stings are mild enough to not require hospitalisation, although the pain may suggest otherwise. Just like other jellyfish stings, vinegar is the standard first aid, and anti-venom may be required in extreme cases.

Jellyfish stings are always pretty bad, but jellyfish are part of the ocean, and as divers we must accept that. Our best defense against them is to wear a wetsuit, and don’t get in the water in areas where they are known to gather at certain times of the year.

It is important to remember that one of these venomous marine creatures will ever attack you, and any incident is either and accident or defence. As long as you remember to never touch or harass an organism, you should be fine, and always take care walking through the shallows or resting on the sea bed.

Do you know of any other super venomous marine animals that you would like to add to our list? If so, stick it in the comments section below and we will get back to you.

‘The Oceans Most Venomous Animals’ was written by Mike