Tentacles meters long that can tangle around you and stingers ready to inject deadly venom. They can be almost entirely seethrough, making them the perfect killer in disguise. Here’s everything you need to about them before you dive into these waters. Here’s How to Survive the 10 Most Dangerous Jellyfish in the World
Number 10: Purple Jellyfish
Earning the self-descriptive purple people-eater title, it’s found near Australia, in the North Sea and throughout the Gulf of Mexico. Sometimes referred to as the mauve stinger, it stays in deep waters during the day, but at night you can easily find it near the surface. Unlike other types of jellies, this one also has stinging cells on its head. Ouch. Don’t let a beached one fool you, though. Purple jellyfish can sting even after they’re dead.
Number 9: Sea Nettle
These sea monsters have a distinctive curved shape and up to 24 long and venomous tentacles. You’ll know if one stings you. The pain is equal to what you’d be dealing with after encountering a bee. Applying ice and cortisone cream can help relieve the discomfort.
Number 8: Moon Jellyfish
It doesn’t mind going for the occasional deep dive, but this floater prefers to flow with warmer surface currents in oceans across the globe. The moon jellyfish’s bell can reach a diameter of 40 cm (16 in). It has shorter tentacles compared to other jellies, but don’t underestimate them. Their sting releases mucus that causes pain, irritation and swelling that’ll take more than a week to subside.
Number 7: Cannonball Jellyfish
Here’s a different type of hunter. This jellyfish has stubby arms instead of tentacles, so when it perceives a threat it attacks with its underwater cannonball. A cloud of mucus that contains toxins harmful to humans. Don’t get me wrong, it still has stingers if you get close. But its first line of defense can trigger a heart attack. You can run into a lot of these cannonballs in warmer waters of the Pacific and Atlantic oceans.
Number 6: Morbakka Fenneri
Reaching 15 cm (6 in) its bell is small enough to fit in your hand, but you better not try to hold one. A single sting can cause everything from back pain to a potentially lethal stroke. Also called the fire jellyfish, it can easily be mistaken for a plastic bag in the water. If you get stung, make sure to keep the freshwater away and instead quickly apply vinegar to help neutralize any toxins.
Number 5: Lion’s Mane Jellyfish
It’s the largest jellyfish on Earth. Its head can be up to 2.4 m (8 ft) wide and its 1,200 tentacles can be almost 36 m (120 ft) in length. Its barbs have a reddish or yellow color that resembles a lion’s mane and they release a neurotoxic venom that can kill almost any prey. You can find this giant in the Arctic, the North Pacific and the North Atlantic oceans. The most important thing to do in case of a painful sting is to get to shore quickly. You may have pieces of tentacle stuck to you, so try to remove them with either a stick or tweezers and douse the area with warm water.
Number 4: Portuguese Man o’ War
Even though technically this isn’t a jellyfish, it can sure sting like one. Or should I say a few of them. This creature is a siphonophore, a colony of organisms working together. Each colony has its own tasks and can’t survive without the others. Man o’ wars don’t swim, but rather get propelled by ocean currents. This way of floating makes it look like the sails of warships used in the 18th century. Their sting can be quite painful, but try to stay still. If you start thrashing around, you can get caught in the tentacles and suffer multiple stings that can trigger anaphylactic shock.
Number 3: Irukandji Jellyfish
This might be the world’s smallest jellyfish, but it sure goes big with the venom. Its bell is the size of a sugar cube and its four tentacles won’t grow longer than 1 m (3 ft), but they’ll sting you so fast that you can’t possibly dodge it. The result is so nasty it’s been branded Irukandji syndrome. You’ll be suffering horrendously painful muscle cramps, a feeling like your skin is on fire and vomiting. If it’s not treated quickly, it can be lethal. There is no antivenom available for the Irukandji sting, so all you can do is treat the symptoms and sweat things out until the venom clears your system.
Number 2: Okinawa Sea Wasp
The runner-up of this list looks. a little different. Its bell is cube-shaped, and its 15 tentacles can be as long as 3 m (10 ft). It’s a speedy swimmer, but if you get stung you better be the one swimming fast. You’d feel muscle cramps, constriction of the throat and delirium. Once the venom enters your body, it can stop your heart within 30 seconds.
Number 1: Australian Box Jellyfish
The well-earned top spot goes to the most venomous marine animal there is. It lives within the ocean waters surrounding Australia and Southeast Asia, and unlike most other jellies it can actively swim and choose the directions it wants to go. If you get stung by this jellyfish, you could be left paralyzed while dealing with cardiac arrest. If enough venom is released, you can die in just a few minutes. Luckily for you, there’s an antivenom that can save your life. Let’s just hope you can make it to the hospital before it’s too late.
- 5 Most Poisonous & Deadliest Jellyfish in the World. Aqua Guides (2021). Scuba.
- Purple Stinger. (2020). Australian Museum.
- Do Lion’s Mane Jellyfish Sting? (2023) American Oceans.
- A jellyfish out of the box. Keable, S. (2018). Australian Museum.
- A Guide to Surviving the Portuguese Man-o-War Invasion. Richmond, B. (2015). Vice.