Box Jellyfish: World's Most Venomous Sea Creature

Key Takeaways

Box jellyfish, belonging to the Cubozoa class, are the world's most venomous sea creatures with up to 15 tentacles containing 5,000 stinging cells that release a toxin causing rapid blood pressure spikes and heart failure.
The Australian box jellyfish is particularly deadly, with its venom capable of causing excruciating pain, vomiting, headaches, anxiety and potentially death if left untreated.
Box jellyfish actively hunt prey using their advanced nervous system and swim at speeds of 4 mph (6 km/h), mainly targeting shrimp and small fish in tropical and subtropical waters.

If sharks can have a week of their own, why not jellyfish — especially the hyper-venomous box jellyfish? Most jellyfish are more bothersome than threatening, which is probably why no one would tune into "Jellyfish Week."

Also known as sea wasps and marine stingers, box jellyfish belong to the Cubozoa class which includes 50 described species. A box jelly can have up to 15 tentacles with about 5,000 stinging cells, known as cnidocysts that it uses to kill prey.

Each of those cells contains a tiny capsule that can fire microscopic stingers into its prey at more than 37 miles (60 kilometers) per hour, releasing a toxin that causes a rapid spike in blood pressure, which makes the heart seize up and kills the victim.

The Most Venomous Marine Animal

While the stinging cells of other jellyfish can hurt pretty bad, the box jellyfish has a powerful venom that can kill you — and make that process as painful as possible. The Australian box jellyfish (Chironex fleckeri), is so poisonous that if one of its 6-foot-long (1.8-meter-long) tentacles touches you, it's possible you might die before you reach the shore.

The Lilliputian jelly (not technically a box jelly but still gnarly), Carukia barnesi, might have you begging to die because the pain, vomiting, headaches and anxiety are beyond excruciating. Occasionally fluid will fill the lungs and, if left untreated, could result in death.

How a Box Jellyfish Sting Works

Dr. Angel Yanagihara, a marine biologist at the University of Hawaii at Manoa, and the world's foremost expert on box jellyfish, says that the box jellyfish does not release venom like a rattlesnake.

Instead, when a box jellyfish stings, it releases a "digestive cocktail" that helps the creature catch and digest its meals. In humans, however, Yanagihara says that digestive cocktail acts like a "molecular buckshot...causing holes in all our cells." A person's heart can stop in as little as five minutes.

"We're a greater threat to them than they are to us," says Yanagihara, who has experienced a box jellyfish sting several times and survived.

How Fatal Is a Box Jellyfish Sting?

Although no one has kept an official fatality record, an estimated 20 to 40 people die each year from box jellyfish stings just in the Philippines. Experts say the mortality rate around the world is higher than what's reported because doctors often misdiagnose the symptoms or simply get the cause of death wrong.

What we do know is that the 43 species of box jellyfish cause more deaths and injuries than sharks, stingrays and sea snakes. You'd have better odds of surviving if bitten by a black widow.

One type of box jellyfish can even cause the dreaded Irukandji syndrome — a combination of muscle-cramping agony, extreme hypertension and potential cardiac arrest.

Where Box Jellies Live

Box jellyfish generally live in the tropical and subtropical regions of the Indo-Pacific Ocean, as well as in the warm waters in the Northern Territory of Australia. You may find some around Hawaii and in warm coastal waters off the Gulf Coast and East Coast. Only a handful of species can be found in all three oceans.

Box jellyfish are among the oldest animals on the planet, dating back at least 600 million years, surviving several mass extinctions.

Box jellyfish numbers, as those of all jellyfish, are growing, exacerbated by warming oceans, and oxygen-depleting fertilizers that eventually find their way into the water. They are most active between November and April (jellyfish season).

Box Jellyfish Actively Hunt Prey

Box jellyfish are a curious breed. For one thing, they have two dozen eyes, most of which have lenses, corneas and irises. In other words, they can see, whereas the anatomy of a regular jellyfish only allows them to distinguish light from dark.

Box jellyfish also have a more advanced nervous system then their cousins, allowing them to quickly avoid — and engage — objects.

Also, unlike other species of jellyfish who wait for their meals, box jellyfish swim as they actively hunt their prey, which is mainly shrimp and small fish. They propel through the water at 4 miles per hour (6.4 kilometers per hour) by opening and shutting their bell-shaped heads, like an umbrella in a rainstorm.