Box Jellyfish Facts – 43 Common questions answered


box jellyfish facts

Box Jellyfish are something to be feared and if you are heading to Cairns for a holiday, you will no doubt have many questions regarding them. 

This article was written to hopefully help you understand these beautiful creatures and at the same time, protect you from them.

Without further ado, here are 43 common box jellyfish questions answered.

1. How many eyes do box jellyfish have?

Box jellyfish have 24 eyes made up of 4 different types.  Four of them are much like our eyes (image forming) and the other 20 are light/dark sensors for obstacle avoidance.  They can make out shapes and distinguish between prey and predators quite easily.

2. Where do box jellyfish live?

Box Jellyfish live mostly on the coast of northern Australia and are frequently found in Queensland, Northern Territory and Western Australia.  They are also found all over Indonesia and the greater Indo-Pacific region. They also live in the northern hemisphere where they tend to accumulate in warmer climates.

3. What do box jellyfish eat?

Box Jellyfish are carnivores that actively hunt their prey by seeing it and chasing it.  They can swim very fast too, faster than an Olympic swimmer. They will eat whatever they can get their tentacles on.  

This includes;

  • Prawns/Shrimp
  • Fish
  • Worms
  • Crustaceans 
  • Other jellyfish

4. Are box jellyfish deadly?

Some species of box jellyfish produce extremely potent venom: Chironex fleckeri, Carukia barnesi and Malo kingi. A sting from one of these jellyfish will hurt like you would not believe, and not only is there excruciating pain but the venom can send the heart a constant state of contraction and the person into ‘shock’ which, sadly, can prove fatal.  Those most at risk are children, elderly and those with existing heart problems.

No data actually exists on the number of people who have died from box jellyfish stings globally, though the current death toll in Australia is at 69.

5. When are you may be most likely to be stung?

On super hot days in summer with very low wind, perfect for jumping in the ocean. Jellies don’t do well with wind or lots of waves so most incidences happen in very still water, less than 0.5 meters deep. So really, it’s about not splashing your feet about in the water if the surf lifeguard flags read RED for no swimming because Irukandji collected that day. Oh and for you NON-AUSSIES out there, yes you lovely naive Brits and Irish, yeah definitely be aware of the flags, green or no flag is good to go and yellow is some risk and red is no swimming.

6. Are box jellyfish endangered?

Not at all.  Box jellyfish are thriving and are in no way endangered.  In fact, with global warming slowly raising the temperature of the ocean, we are seeing longer stinger seasons.  Warmer oceans provide an ideal situation for box jellyfish to feed and breed. Increased ocean temperatures will no doubt lead to a greater amount of stings.  

7. Are box jellyfish dangerous?

Yes, very dangerous actually.  They have frequently been called “The world’s most venomous animal”.  Box jellyfish venom can easily kill a fully grown human, so yes, they are dangerous.

8. Are box jellyfish in Cairns?

You bet there are!  They hang off the coastal beaches in the warmer months and stings are actually pretty common up this way.  All of the stings happen at the coastal beaches and not the Great Barrier Reef, which is good news for tourism.  

9. How do box jellyfish reproduce?

The reproductive cycle of a box jellyfish is no different to most other types of jellies. The adult jellies, called medusas, release eggs and sperm into the water. The egg is then fertilised, eventually settles and becomes a small (~1mm) primary polyp (imagine a tiny upside-down jellyfish). As a polyp, the jellyfish can reproduce asexually through a process known as budding. A small clone grows on the polyp and separates. Finally, upon an environmental cue, the polyp breaks off from the hard surface it was growing on, undergoes a change and turns into the free-swimming jellyfish that we all love to fear.

10. How many box jellyfish are there in the world?

This has never been researched and I highly doubt it ever will be.  The size of the area that they live in is simply too massive. The official answer to this question is…. Too bloody many.

11. Can box jellyfish get inside of the stinger nets?

Normally you are pretty safe against boxies inside the nets, though smaller boxies and the much smaller Irukandji frequently get inside the nets.  The nets are like a seatbelt, as in, it may not be 100% but it’s better than nothing.

12. How many species of box jellyfish are there?

There are currently approximately 40 known species of box jellyfish.  Box jellyfish is a collective term for Cubozoa which is basically a general term for jellyfish with a cube-shaped head and venomous tentacles. 

13. How much does a box jellyfish cost?

While it’s not technically illegal to keep a boxy as a pet, you will be hard-pressed getting one.  There are no pet shops in the world that deal with these animals due to the extremely difficult handling and caring process.  Being able to catch or breed these animals is something that only the very best scientists should be attempting. All of the box jellies in captivity are being used for research.

14. Can you have a box jellyfish as a pet?

Yeah… sure.  If you have seen Seven Pounds with Will Smith, you no doubt saw his jelly tank.  The thing is, you can’t buy them so you will have to collect your own. Collecting from marine parks is illegal, so you would have to be in the right place at the right time outside of a marine park.  The tank must have a very slow filtration and their feeding patterns need to be matched to their wild feeding patterns. The water must be changed weekly with fresh saltwater of the same salinity and alkalinity.  They will perish very quickly without proper care. 

The first sign of an unhealthy box jellyfish is that it will shrink in size and lose the square shape of its bell.

15. When are box jellyfish in Queensland, Australia?

Technically they can be found here all year round, though their activity is certainly greater in the summer season.  Summer here is November to May.

16. When is box jellyfish season in Thailand?

Thailand doesn’t really have a winter as it’s so close to the equator.  This means that box jellyfish activity is pretty high all year round.  

17. Where are box jellyfish found?

Boxies (Chironex fleckeri) will almost always be close to the coastline rather than out on the Great Barrier Reef.  They prefer to hang around fish nurseries as there is plenty to eat. Large ocean passages could see them going without food for quite some time.  The most common place to find them is near estuary and river outlets where they can catch animals being flushed out from inland. 

18. Why are box jellyfish so deadly?

Their venom is considered to be among the most deadly in the world.  It contains toxins that attack the heart and nervous system. The pain experienced from a boxy sting will be excruciating and can often send people into ‘shock’.  Shock is normally what kills people after being stung by a box jellyfish.

19. Are box jellyfish and Irukandji jellyfish the same?

Yes and no. 

Yes, the Irukandji jellyfish also have a cube/bell-shaped head and no, because in many other ways they are very different from the large box jellyfish. Most notably, Irukandji are much smaller and can be found both at the beaches and out at the Great Barrier Reef. 

Fun fact: The Irukandji gets its name from the indigenous tribe that resided in the area where the first Irukandji was found. But that’s a whole other story

20. Are box jellyfish immortal?

While there is a jellyfish that is essentially immortal (Turritopsis dohrnii), the box jellyfish is not.  We actually do not know how long box jellyfish will normally live for but it has been estimated at around 2 years.  In this time, they may only spend 1 year as a medusa (aka an adult). Box jellyfish can also die from wounds sustained by speed boats, coral and other obstacles they didn’t manage to avoid.

21. Are box jellyfish native to Australia?

Being that the boxy is a migrating ocean animal, it’s hard to determine exactly where they came from.  It is fair to say the box jellyfish is, in fact, native to Australia as we have no evidence to prove otherwise.  

22. Are box jellyfish poisonous?

No, they are not poisonous at all, they are highly venomous.  Venom and poison are completely different things. Venomous is like a snake or spider, venom is injected into our skin.  Poison is something that occurs when we ingest something we shouldn’t. 

For more info on the difference between venom and poison, check out this Encyclopedia Britannica page.

23. Can box jellyfish be eaten?

Jesus Christ…. Why did you type that into Google?  Do not EVER attempt to eat a box jellyfish. There is no culture in the world that does that, even the Japanese don’t touch them.

24. Can box jellyfish kill a shark?

Yes, they can! Though not the kind of shark you are thinking about.  Small baby sharks who have not yet developed their thick skin could be stung and killed by a large adult box jellyfish.  It’s never been recorded on film though small dead sharks have been found with clear jellyfish tentacle marks on them.

25. Can box jellyfish live in cold water?

Technically speaking, yes.  They have been found in Melbourne before.  This is super rare though as they like warm tropical waters.  The box jellyfish that are found in colder waters, no doubt got stuck in fast-moving currents that carried them far from where they want to be.

26. Can box jellyfish live in freshwater?

This will scare you…. Box jellyfish can be found in brackish water such as in estuaries, mangroves and creeks that have a slow tidal effect connected to the ocean.  Brackish water is when freshwater meets seawater such as when a river meets the sea. Boxies have never been found in pure freshwater. 

27. Can box jellyfish see?

Unlike us, box jellyfish have 24 eyes, so they can actually see quite well.  They cannot see your flash new watch but, they can determine if you are threatening or edible.

28. Can box jellyfish sting dogs?

Even your doggo isn’t safe from these jellies.  Box jellyfish can easily kill a canine with a sting.  There have been many news stories on this over the years.  Be careful when letting your dog run around the beach, if there are jellyfish warning signs then look after your pet and keep them out of the water.

29. Can box jellyfish sting through wet suit / stinger suit?

Finally some good news!  A wetsuit acts like a suit of armour for humans against jellyfish stings.  The material of the wetsuit is more or less an exoskeleton. We only get stung when the jellyfish stinging cells hit our naked skin.  So in the words of the great Barney Stinson, “Suit Up”.

30. How box jellyfish venom works?

Once a tentacle of the box jellyfish touches your skin, it activates nematocysts filled with venom which use harpoon-like dispensing artillery that inject venom through the skin. Nematocysts, which are like water drops, have the fastest biological reaction on the planet.  They discharge in 700 nanoseconds, which is about 7000 times faster than we can blink. Once discharged, the venom will enter your body and head straight for the nervous system and heart.  

Box jellyfish venom causes your heart cells to develop pore-sized holes that allow potassium leakage and prevents the heart muscles from relaxing. This can lead to cardiovascular collapse and death, in as quickly as 2 to 5 minutes from when you are stung by more than 2 meters of a tentacle.  CPR is mostly ineffective because of the heart’s inability to relax and contract.

We need to remember that these are not evil creatures, they are just highly evolved predators designed to kill their prey.  

31. How many babies do box jellyfish have?

Thousands, and then each baby can (once settled) clone themselves.

32. How often do box jellyfish eat?

Box jellyfish will generally eat 2 or 3 times per day depending on the available food.  If they have a huge supply then they have been seen eating up to 7 times per day. With a metabolic rate faster than a V8 engine, for box jellies the more food the better!

33. How often do box jellyfish reproduce?

It is not known how often box jellyfish reproduce. Some reports estimate that some box jellyfish will only breed once or twice in their life.  Much like most bloggers.

34. What do box jellyfish look like?

As pictured throughout this article, you can see that box jellyfish always have a cube-shaped head with clearly visible tentacles coming from four corners parts of the bell.  They can have up to 15 tentacles and be anywhere from an inch to 10 feet in total length.

35. When was the box jellyfish discovered?

The Box jellyfish (Chironex fleckeri) was named after North Queensland toxicologist and radiologist Doctor Hugo Flecker.  On January 20, 1955, when a 5-year-old boy died after being stung by a boxy at Cardwell, North Queensland.  Flecker found three types of jellyfish in the area. One was an unidentified box-shaped jellyfish with groups of tentacles arising from each corner (Chironex fleckeri).

Flecker sent it to Dr Ronald Southcott in Adelaide, and on December 29, 1955, Southcott published his article introducing it as a new genus and species of lethal box jellyfish. He named it Chironex fleckeri, the name being derived from the Greek cheiro meaning “hand”, the Latin nex meaning “murderer”, and “fleckeri” in honour of its discoverer.

36. Where do box jellyfish go in winter?

While there is no scientific evidence, it is thought that box jellyfish either die or will head out to sea in winter.  There have been reports from the fisherman on prawn trawlers that boxies swim to great depths and have been pulled up in the prawn nets.  

Not all boxies will leave Australian shores in winter though, some will hang around, so it’s always important to protect yourself when swimming in the northern parts of Australia.

37.  What does a box jellyfish sting feel like?

This I can answer with personal experience.  It feels like a live electrical cord whipping you for about 5 hours non-stop.  On top of this, your body becomes quite uncontrollable and you will most likely become a cold, sweaty mess huddled in the fetal position on the floor.  The pain will die down that day, though this could be from the morphine.  

The sting area will be tender, scarred, bleeding and hot for several days.  It will take around a week to fully regain control of your body as the toxins get filtered out.  Please keep in mind that I was a very fit and healthy 22-year-old when I was stung. A 70-year-old with a heart stent probably won’t be lucky enough to experience the pain for any more than an hour.

38. How do box jellyfish hunt?

They eat by catching their prey using their tentacles by immobilizing them with their venom and putting the unfortunate creature into the underside of their bell. They also poop from the underside of their bell.

39. Are there any differences between juvenile and adult box jellyfish?

Yes, juvenile boxies have invertebrate specific venom, for prey such as prawns and crustaceans, whilst adults have vertebrate-specific venom for their natural prey such as fish or unlucky humans. So it is the adults, these are the chaps that we need to be super cautious not to come in contact with.

40. Night diving – Are jellyfish attracted to the light from your diving torch?

Yes, it is a well-known fact that most jellyfish are attracted to light, including the box jellyfish. Box jellyfish in captivity have been observed to follow a lit match across their tank. Take home message…….Divers be aware!

Fun fact: Box jellyfish react quite differently to blue light. Instead of coming straight towards the light as they do with white and yellow lights, perform a reduced speed figure 8 pattern dragging their tentacles through the brightest part of the blue light.  While this phenomenon has been observed hundreds of times it is yet to be explained…..spooky!

41. Why are there more stings when there are onshore northerly winds?

If you work on the ocean, then it is pretty common knowledge that box jellies are brought onshore by northerly winds. When there are light northerly winds, there is less wave activity which is thought to enable boxies to swim around easier.  It is also thought that there are more box jellyfish up in the northern regions of Australia, and therefore they are brought down south by northerly winds. 

There is scientific evidence linking northerly winds to increased numbers of reported stings but this may also be due to several other factors. When there are northerlies the ocean is calmer and this results in more people physically being in the water and therefore more chances of stings occurring.    

42. Are there more box jellyfish stings after it rains?

Yes, there are more reported box jellyfish stings after a good amount of rain because Chironex fleckeri lives in estuaries and rivers which get flushed out after heavy rain.

43. What is a group of box jellyfish called?

This is perhaps the only amusing thing about box jellyfish, collectively they are known as a SMACK, which makes sense because a sting from a boxie will hurt nearly as bad as your Mum’s wooden spoon.

In summary

Box jellyfish are indeed quite frightening animals.  They have evolved over millions of years to become one of the oceans top predators.  When humans and supreme ocean predators mix, the result is never good. In order to protect yourself, you should remember what you have read here and never enter waters that could contain box jellyfish without being suited up.  

If you are travelling to Cairns then make sure you have some sort of health insurance, just in case you need to spend a few days in the hospital recovering from a sting.

This article has been fact-checked by several Marine Biologists, PhD Candidates, Nurses and Lifeguards.

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