How to Survive a Box Jellyfish Sting

Believe it or not, a tiny little jellyfish takes the title for the most venomous creature on Earth! Just getting part of a tentacle on your skin is enough to kill a person within 2 minutes. We know this deadly creature as the box jellyfish. 

I hope that got your attention because if you happen to visit anywhere in tropical Australia or the Indo-pacific, you need to listen to this! It may save your life.

This is one of the few marine animals I feel it’s ok to start with a paragraph talking about how quickly it could kill you. Part of the reason for that is that far too many people die from what could be a preventable encounter. You just need to know a bit about these animals to appreciate them, avoid them, and not end up in the hospital, or worse, the grave.  

The Box Jellyfish Basics

Scientists have currently identified 51 species of box jellyfish worldwide. It’s estimated that between 50 and 100 people die a year from encounters, but that estimate may still be low. Many incidents go unreported since they occur throughout the indo-pacific in poor, remote places. 

Some box jellyfish are small, about the size of your thumbnail. Others have bells the size of a basketball – with 10 feet of tentacles trailing behind them. All have the ability to inflict painful stings and a few are well known to quickly kill a human. 

Here I’ll primarily discuss how to survive Australia’s box jellyfish (Chironex fleckeri). It is the biggest and arguably deadliest. It’s commonly called the Indo-Pacific box jellyfish or Flecker’s box jellyfish. 

Unlike other jellyfish, box jellyfish actively swim and hunt for their prey! An adult can swim upwards of 4 knots in short bursts – that’s as fast as you can walk. In addition, they have eyes. They’re not exactly like ours, but they do detect rudimentary images and use them to see in all directions. They can see dark objects better than light objects and will actively avoid them in the water. This is one reason dark clothing is better than light when in box jellyfish waters.

A box jelly has clusters of 15 tentacles that attach at the four corners of the box-like medusa – that makes a total of 60 tentacles. Each tentacle can be up to 10’ long, and scientists estimate an adult man only needs about 6’ or 7’ of tentacle to touch them to provide a lethal dose of venom. That means a box jellyfish has enough venom to kill nearly 60 humans. 

Venom is injected in the same way it is with other cnidarians, such as the Portuguese man-o-war that we discussed in the previous chapter. Small cells with nematocysts will fire upon touch or chemical stimulation. In this case, there are hundreds of thousands of nematocysts that fire per sting. These hooked, dart-like syringes dispense the venom into their prey – or our skin. A box jelly is estimated to have about 5 billion nematocysts!

The venom of a box jellyfish is different from other stingers. It’s a complex concoction of different compounds, none of which are very well understood. We know it contains a multitude of compounds that, when injected together, work very effectively to immobilize and kill their victims. For humans, it acts in three main ways.

1 – It causes severe skin death. That results in permanent scarring of the skin. 

2 – It destroys blood vessels. 

3 – It produces intense muscle spasms that are so severe that muscles of the heart can’t relax  between contractions, stopping blood flow. 

Symptoms of a box jellyfish sting Include

  • pain, itching, rashing, welts. 
  • nausea, diarrhea, swollen lymph nodes, coma, muscle spasms, death.
  • heart failure

Fortunately there is an antivenom, which many lifeguard stands within box jellyfish territory do carry. Unfortunately, the venom acts so quickly that if it’s not administered right away it may be too late. 

What the Box Jellyfish Venom Does

The venom is a component of many things. Each acts on a different part of the body. One component causes localized pain. Another component travels through veins and arteries straight to the heart. After a sting, the pain comes on quickly and continues to get more intense and widespread through the body – ratcheting up the pain with each passing moment. 

Scenarios to Avoid with Box Jellyfish

This general advice applies to all areas of the box jellyfish’s range, but is especially important in the warm, murky waters of Australia’s north-eastern coast in summer. This area is home to crocodiles and box jellyfish, so this info is a bit of a two-for-one avoidance strategy.

  • First, always wear protective clothing. Any kind will do. Lycra suits or even pantyhose will reduce risk while swimming, especially in the summer months. 
  • Swim only on patrolled beaches, preferably in netted swimming areas. 
  • Do not run or dive into the water; walk in slowly. 
  • Do not allow children to enter the water without protective clothing, nor to swim unsupervised during the summer danger season. 
  • Take the trouble to be educated in the fundamentals of rescue and resuscitation from a sting by a box-jellyfish.

The Most Dangerous Box Jellyfish

The most dangerous of the 51 species of box jellyfish is the Australian box jellyfish (Chironex fleckeri) which is why I’m highlighting it specifically here. Others (like Malo kingi and Carukia barnesi) may be called by the common name Irukandji jellyfish. They’re often very small (an inch or less), but they pack enough venom to kill a human. Novelist Robert Drewe described the sting as “100 times as potent as that of a cobra and 1,000 times stronger than that of a tarantula’s.”

Let’s not forget that there are types of box jellyfish all over the world. The Caribbean and Gulf of Mexico, for instance, have a species that is capable of killing a human as well.

How to Survive a Box Jellyfish Sting? 

  • Immediately get out the water, before you possibly lose the ability to swim and drown.
  • Pick off the tentacle if it’s still on the body. Make sure not to touch it with bare hands – use gloves or utilize a piece of clothing or a towel. 
  • Rinse with vinegar if it’s available. Do so generously. While there is still some debate whether or not this is helpful, it’s not harmful. 
  • Get immediate medical attention. If anti-venom is available, it can be given to counteract the effects of the venom. 

There are some important things not to do too.

  • Don’t pee on the sting or tentacles.
  • Don’t rub the area that is stinging.
  • Don’t put baking soda on the sting.

All of these actions are likely to cause more nematocysts to fire – increasing your dose of venom.

Prefer to Listen?

If you’d rather listen to this article about box jellyfish stings and safety, I recorded this for you.

Videos about Box Jellyfish

If you enjoyed this article, you might enjoy this selection of youtube videos as well.

About The Author
Rob Nelson

Rob Nelson

Rob has worked as a biologist and wildlife educator since 2001 with the goal of reconnecting people with nature. While in grad school in Hawaii he studied ecology and as a side job he spent years working part time leading nature tours – teaching about the wildlife, the land, and the natural history that made the islands so unique. These were the first sparks that would lead to what is now StoneAgeMan.