Box Jellyfish: The Deadliest Marine Creature on Earth

If sharks can have their own week, why not give the highly venomous box jellyfish its own time in the spotlight? Unlike most jellyfish, which are more of an inconvenience than a danger, the box jellyfish packs a lethal punch, making 'Jellyfish Week' an unlikely TV event.

Known as sea wasps and marine stingers, box jellyfish are part of the Cubozoa class, which includes 50 identified species. A box jellyfish can have up to 15 tentacles, each equipped with about 5,000 stinging cells, called cnidocysts, that it uses to paralyze and kill its prey.

Each of these cells holds a minuscule capsule capable of launching microscopic stingers into its prey at speeds of over 37 miles (60 kilometers) per hour, injecting a venom that triggers a rapid spike in blood pressure, causing the heart to fail and ultimately killing the victim.

The Most Venomous Marine Animal

Though the stings of other jellyfish can be intensely painful, the box jellyfish's venom is so potent that it can be lethal — and the process of dying is often excruciating. The Australian box jellyfish (Chironex fleckeri) is so dangerous that if one of its 6-foot-long (1.8-meter-long) tentacles brushes against you, you might die before even making it to shore.

The tiny but terrifying Carukia barnesi, also known as the Lilliputian jelly (not technically a box jellyfish but still a menace), can leave you begging for death due to the unbearable pain, nausea, headaches, and anxiety. In severe cases, fluid may accumulate in the lungs, and if untreated, it could lead to death.

How a Box Jellyfish Sting Works

Dr. Angel Yanagihara, a marine biologist at the University of Hawaii at Manoa and the leading global authority on box jellyfish, explains that the box jellyfish doesn't release venom in the same way a rattlesnake does.

Instead of venom, when a box jellyfish stings, it secretes a 'digestive cocktail' that aids in capturing and breaking down its prey. However, for humans, this cocktail acts like 'molecular buckshot,' causing damage to every cell. According to Yanagihara, a person’s heart can stop in as little as five minutes.

"We are a bigger threat to them than they are to us," says Yanagihara, who has been stung by a box jellyfish multiple times and lived to tell the tale.

How Fatal Is a Box Jellyfish Sting?

While there's no official record of fatalities, it's estimated that between 20 to 40 people die annually from box jellyfish stings in the Philippines alone. Experts suggest the global death toll may be even higher, as doctors frequently misdiagnose the symptoms or fail to identify the actual cause of death.

What we do know is that the 43 species of box jellyfish are responsible for more deaths and injuries than sharks, stingrays, and sea snakes combined. In fact, you'd have a better chance of surviving a bite from a black widow.

One type of box jellyfish can even trigger the feared Irukandji syndrome — a horrific condition that causes muscle-cramping pain, dangerously high blood pressure, and the risk of cardiac arrest.

Where Box Jellies Live

Box jellyfish are typically found in the tropical and subtropical regions of the Indo-Pacific Ocean, as well as in the warm waters of the Northern Territory in Australia. You may also encounter them around Hawaii and along the Gulf Coast and East Coast. Only a few species live across all three oceans.

Box jellyfish are among the oldest living creatures on Earth, with a lineage stretching back over 600 million years, surviving multiple mass extinctions along the way.

The population of box jellyfish, like all jellyfish, is on the rise, driven by warmer oceans and the influx of oxygen-depleting fertilizers that eventually reach the water. They are most active from November to April, during jellyfish season.

Box Jellyfish Actively Hunt Prey

Box jellyfish are an intriguing species. For one, they have 24 eyes, many of which feature lenses, corneas, and irises. This allows them to actually see, unlike typical jellyfish, which can only sense light from dark.

Box jellyfish also possess a more sophisticated nervous system than most other jellyfish, enabling them to quickly avoid or engage with objects around them.

Unlike other jellyfish species that passively wait for food to come to them, box jellyfish actively hunt their prey, which mainly consists of shrimp and small fish. They swim at speeds of up to 4 miles per hour (6.4 kilometers per hour) by rhythmically opening and closing their bell-shaped bodies, much like an umbrella in a downpour.