Box Jellyfish: World's Most Venomous Sea Creature

By: John Perritano  | 
Box jellyfish
The box jellyfish (Chironex fleckeri), also known as a sea wasp or marine stinger, releases a toxin so powerful that it causes a rapid spike in blood pressure, which can cause cardiac arrest and lead to death. Auscape/Universal Images Group/Getty Images

If sharks can have a week of their own, why not jellyfish? Is it because jellyfish do not have a menacing maw, or a fear-inducing dorsal fin? Is it because no one's made a sinister movie where jellyfish terrorize beachgoers? Or is it because jellyfish look like squished gummy bears with spaghetti strings for tentacles, while many sharks have razor-sharp teeth that can rip into human flesh?

Let's face it, jellyfish are more bothersome than threatening, which is why no one would tune into "Jellyfish Week." Sure, their stings hurt and itch, but sharks can tear a limb off. If that doesn't get you your own show, nothing will.


Most Venomous Marine Animal

But what if we told you there's a type of jellyfish that is more menacing than the most threatening shark. It goes by the scientific name Cubozoa, but is more commonly referred to as the "box jellyfish."

Unlike their annoying cousins, the box jellyfish has a powerful venom. How powerful? One type of box jellyfish, Chironex fleckeri, also known as the Australian box jellyfish, 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. It is considered the most venomous marine animal on the planet.


On the other hand, if you were stung by the Lilliputian Carukia barnesi, you might beg 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.

Box jellyfish live generally in their own neighborhoods in the Indo-Pacific Ocean and in the waters off Northern Australia, although they also inhabit the waters around Hawaii and off the Gulf Coast and East Coast. Only a handful of species can be found in all three oceans.

Also known as sea wasps and marine stingers, box jellyfish, a class that includes 50 described species, 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.

Although no one has kept an official fatality record, between 20 and 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 misdiagnosis the symptoms or simply get the cause of death wrong. What is known, 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.


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. 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.

Here's what might be the worst part: 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 (6.43 kilometers per hour) by opening and shutting their bell-shaped heads, like an umbrella in a rainstorm.


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. Yes, you don't want to experience a box jellyfish sting.

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).

"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.