What Jellyfishes are Poisonous? (8 Deadliest Jellyfishes)

Remember the famous movie Beauty and the Beast? Well, jellyfishes tend to combine both characters into one. Beauty for the jellyfish’s luminous and awe-inspiring charm, and Beast for how poisonous its sting could be. With 150 million people stung by a jellyfish annually, you may be curious: what jellyfishes are poisonous?

Jellyfish species like the sea wasp, sea nettle, Portuguese Male o’ War, and Irukandji are some of the deadliest jellyfishes around. Stings from these species can cause unbearable pain to the victim. Worse still, if such stings are not treated promptly, the individual can suffer cardiac arrest and, in some cases, death.

There is a lot to learn about the fatality of jellyfish stings. Which jellyfish species are the most poisonous? Where do such species live? How can you know if a jellyfish have poisoned you?

These are some of the questions we will address in this guide.

How Many Species of Jellyfish are Poisonous?

There is a multitude of Jellyfish species. Currently, scientists estimate that over 2000 jellyfish species exist today.

Relax, not all 2000 species sting. Around 70 Jellyfish species have been identified to have poisonous stings.

The poisonous species tend to reside in the ocean regions like the Southern, Pacific, and Indian Oceans.

What are the Top 8 Deadliest Jellyfishes? 

While not all jellyfishes are deadly, some stand head and shoulder above their peers in the fatality of their sting. Here are some of the deadliest jellyfishes.

Australian Box Jelly (Sea Wasp)

The Australian Box jelly (also known as Chironex Fleckeri) is hands-down the most dangerous jellyfish you can come across.

So notorious is its sting that it was tagged the Sea Wasp.

But here is where it gets even more difficult. You can’t see this box jelly – making them harder to avoid.

The Australian box jelly’s venom is so powerful that it can kill a grown man with a dose as supposedly negligible as a single grain of salt!

Critical pains often accompany stings from this box jellyfish. If such stings are not quickly medically attended to, the victim can suffer heart failure and die.

The Australian box jelly naturally resides in the Australian coastal waters, with substantial populations distributed across New Guinea.

Portuguese Man o’ War

This jellyfish is equipped with a bladder stacked with gas. This acts as a floating mechanism, maneuvering its ways to the tides and currents.

Portuguese Man O’ War tends to have purple and pink nests. As exciting as this fish looks, it is a naughty guy.

It is abundantly furnished with poisonous microscopic nematocysts. A sting from these can outrightly kill a fish. A sting from the Portuguese man o’ War has been reported to kill adult humans as well.

This jellyfish inhabits subtropical waters like the Atlantic coast and the Florida Keys.

Sea Nettle

The Sea Nettle is principally resident in Indo-Pacific waters. Sea nettles readily stand out for their lengthy golden-brown bell. Specifically, some bells can grow up to three feet long.

The Sea Nettle’s tentacles closely follow its bell. These tentacles can deliver a burning sting, which can be horrifying.

These stings can be fatal if they trigger a severe allergic reaction.

Morbakka Fenneri

The Morbakka Fenneri is one of the biggest species on this deadly compilation. This species can grow up a bell as wide as two inches (in diameter) and a body as long as four inches.

It is decked with a tentacle at every corner. Particularly, its stings are excruciating. Its stings can also trigger serious Irukandji syndrome in its victim.

Such victims would feel a longing for imminent death as they get overwhelmed with hypertension, muscle cramps, and cardiac arrest.

The MorbakkaFenneri is found chiefly around calm waterways, preferring the warmer marine areas off the coast of Queensland.

Irukandji Jellyfish

This is one tiny miscreant you don’t want to come across. While one of the smallest jellyfishes around, it is notorious for being one of the most poisonous.

Its sting is primarily responsible for the Irukandji Syndrome. For context, its sting can cause you to feel a piercing burning sensation that could last up to half a day.

Stings from this jellyfish can also provoke painful stomach aches, recurring muscle cramps in the arms and legs, and nausea.

While this fish is predominantly resident in Australia, significant populations of this species have been found lately in Thailand, Japan, the British Isles, and even Florida.

Alatina Alata

The Alatina Alata was previously known as the Carybdea Alata. Its sting is admittedly not the most fatal, but the venom is discomfiting.

The Alatina Alata mainly inhabits Hawaiian bay areas and Pakistan beaches in the Arabian Sea.

Lion’s Mane Jellyfish

The Lion’s Mane jellyfish is a giant among the jellyfish community. With tentacles as long as 100 feet and a bell of 8 feet, this jellyfish is the biggest species scientists have discovered so far.

Its sting is not as poisonous as the Australian box jelly but is nonetheless unpleasant and can even get deadly.

The Lion’s Mane Jellyfish (being a Coldwater species) is primarily resident in the North Atlantic and the colder Australian waters.

Chiropsalmus Quadrigatus

The Chiropsalmus Quadrigatus closely mirrors the ChironexFleckeri – only that the former is smaller. But you would be in for horror if you mistake the smaller ChiropsalmusQuadrigatus for being more hospitable.

This jellyfish’s sting is a nightmare, harrowing and other complications like breathing failure, cardiac arrest, pulmonary edema. In extreme cases, a Chiropsalmus Quadrigatus sting can be fatal.

This jellyfish majorly thrives in the Western Atlantic Oceans.

What Jellyfish are Not Poisonous? 

Not all jellyfish species are dangerous. Let us tell you about some harmless species.

Aurelia Aurita (Moon Jelly)

The Aurelia Aurita is more popularly referred to as the Moon Jelly. It is one of the most famous harmless jellyfish species. It is a staple in China, given how delicious it is.

Its gonad and marginal tentacles are packed in four circles. The Moon Jelly’s umbrella can get as long as 40cm, with the manubrium furnished with four sizable oral arms.

Pleurobrachia Bachei

Admittedly a mouthful of a name. This fish, more easily referred to as sea gooseberries, are pose zero harm to humans.

Of course, they hunt prey with their tentacles decked with colloblasts. These colloblasts are adapted sticky cells. But these jellyfishes don’t sting.

They are small, rarely growing bigger than 3cm. They leverage their vibrating hairs in steering and swimming.

They commonly live in the waters off California.

Aequorea Forskalea

The Aequorea Forskalea is also called the Crystal Jelly. You can readily identify this jellyfish from its radial canals. These canals link up the edge of the fish’s flat bell with its center.

Aequorea Forskalea is harmless as its sting cells don’t hurt. This jellyfish rarely grows longer than 10cm and lives more in the coastal areas.

Rhopilema Verrilli

This jellyfish is more readily known as the Mushroom Jellyfish. It packs quite a lot of unique features.

Most distinguishable among these characteristics is its umbrella head carved like a mushroom. This jellyfish also stands out for its creamy white color and central tentacles embellished with dark stripes.

The RhopilemaVerrilli is harmless, preferring to live in gulfs and bays.

Porpita Porpita

This jellyfish is famously referred to as the Blue Botton. Its body uniquely combines a polyps colony and a golden brown (and round) float. The float’s width rarely exceeds an inch.

The polyps colony serves as the Blue Button’s tentacles, with the color varying from yellow to sharp blue.

The PorpitaPorpita doesn’t sting. However, there are cases where this jellyfish irritates your skin.

How Can You Tell If a Jellyfish is Poisonous?

Unless you know the jellyfish species, you are unlikely to tell which fish is poisonous from a glance.

But you can tell a jellyfish’s sting has poisoned you if you notice symptoms like stinging pain, sharp burning sensation, swelling, itching, and tentacle prints on your skin.

In more severe cases, you may experience difficulty breathing, dizziness, nausea, and heart issues.

Are Jellyfish Poisonous to Dogs?

Commonly, dogs are less susceptible to jellyfish poisoning than humans. They rarely die from a jellyfish sting.

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