box jellyfish quick facts
- There are about 50 species of box jellyfish.
- Some box jellyfish eyes have a lens, cornea, iris and retina.
- Box jellyfish can swim at almost four knots.
- Chironex fleckeri has tentacles up to 10 feet (3 m) long.
- The deadliest box jellyfish live mainly off northern Australia and in the Indo-Pacific.
Stay safe: where box jellyfish live, swim only at patrolled beaches. Stay inside the stinger nets if there are any. Always do what the lifeguards say.
What is a box jellyfish?
A box jellyfish has a bell shaped like a cube, or box. Long tentacles trail from each of the four corners.
Box jellyfish are not like most other jellyfish. Scientists put them in a group of their own, the Cubozoa. The name means “cube animals”. There are about 50 species.
Some box jellyfish are harmless to people. A few carry very strong venom. The worst is Chironex fleckeri, which lives off northern Australia. People there call it the sea wasp.
Meet the cube animals
- What group do scientists put box jellyfish in?
- What does the name Cubozoa mean?
- What do people in northern Australia call Chironex fleckeri?
What box jellyfish look like
Box jellyfish are almost see-through. That makes them very hard to spot in the water.
The bell runs from 1 cm to 30 cm across, depending on the species. The biggest is Chironex fleckeri. Its bell is about a foot (30 cm) wide. Its thick tentacles reach 10 feet (3 m).
The tentacles hang in bunches from each corner of the bell. Millions of tiny stinging cells cover them.
Not all of them are giants. The Caribbean box jellyfish is a small kind. It lives in the warm waters of the Caribbean.
| Box jellyfish at a glance | |
|---|---|
| Group | Cubozoa, about 50 species |
| Largest and deadliest | Chironex fleckeri, the sea wasp |
| Bell | from 1 cm to about 30 cm across |
| Tentacles | up to 3 m long in the largest species |
| Speed | almost 4 knots (about 7 km/h) |
| Stinger season in Queensland | usually November to May |
A jellyfish that can see
Most jellyfish have no eyes at all. Box jellyfish have 24, in bunches on each side of the box.
Some of those eyes are a surprise. The US Ocean Service says they have a lens and a cornea. They have an iris that shuts in bright light, and a retina. That is much like our own eyes.
A box jellyfish has no brain like ours. So scientists are still working out how it uses those eyes. Some of them look upwards. They may help the jellyfish steer by the shapes above the water.
Fact or myth: jellyfish eyes
- Box jellyfish have 24 eyes.
- Most jellyfish have eyes just like box jellyfish do.
- Some box jellyfish eyes have an iris that shuts in bright light.
- A box jellyfish has a big brain like ours to handle its eyes.
- Some box jellyfish eyes look upwards.
Swimmers, not drifters
Most jellyfish drift wherever the water takes them. Box jellyfish can swim.
They squeeze the bell to push water out behind them. That gets them to almost four knots, about 7 km/h. A good human swimmer moves at about that speed.
Sight and speed let them hunt. Other jellyfish wait for food to bump into them.
What box jellyfish eat
Box jellyfish eat small shellfish, such as shrimps. They also eat fish and plankton, which are tiny floating animals.
When prey touches a tentacle, the stinging cells fire. The venom stuns or kills it. The tentacles then pull the food up to the mouth, under the bell.
Match the box jellyfish facts
- Top speed — Almost four knots
- How it swims — Squeezes its bell
- Food — Shrimps, fish and plankton
- Mouth — Under the bell
- Body you can see through — Hard to spot in water
How the sting works
The stinging cells are called nematocysts. Each one is a tiny coiled harpoon, loaded with venom.
Brush against a tentacle and thousands of those darts shoot out. They inject the venom in a fraction of a second.
A sting from Chironex fleckeri brings sudden burning pain. It leaves whip-like marks on the skin, often with bits of tentacle stuck to them. The venom can stop a person moving, and it can stop the heart within minutes. Few animals in the world carry venom this strong.
Why is the venom so strong?
Why would a jellyfish need venom this strong? Scientists point to its body. A box jellyfish is very delicate, and so are its tentacles.
A fish that fought for long could tear them. Venom that works in seconds stops prey before it can escape or do damage.
They are not dangerous to every animal. Some sea turtles eat them. The stings do not seem to harm the turtles.
Why such strong venom?
- Why do scientists think box jellyfish need such strong venom?
- Which animal eats box jellyfish without seeming to be harmed?
- What does a Chironex fleckeri sting leave on the skin?
Where box jellyfish live
Box jellyfish live in warm water near the coast, all over the world. The worst kinds keep to the Indian and Pacific Oceans. They live from Thailand and the Philippines to the seas off northern Australia.
In Australia, Chironex fleckeri keeps to shallow tropical water. That means north of Agnes Water in Queensland, all round the Northern Territory, and down the west coast as far as Exmouth. It is one of the most dangerous animals in Australia.
They are commonest in the warm, wet months. Australians call that stinger season. It usually runs from November to May. Beaches in the north then put up warning signs and stinger nets.
Staying safe
People who live in or visit northern Australia know how to stay safe around box jellyfish.
Swim at patrolled beaches: lifeguards know when stingers are about. They put up flags and signs.
Use stinger nets: some beaches have enclosures in the water that keep most jellyfish out.
Cover up: a full-length stinger suit or wetsuit gives your skin protection.
Get help straight away: anyone stung by a box jellyfish needs help at once. Call a lifeguard, and phone for an ambulance.
Stinger season smarts
- When does stinger season usually run in northern Australia?
- What are stinger nets?
- Which of these is NOT one of the guide's ways to stay safe?
First aid for a box jellyfish sting
A box jellyfish sting is an emergency. Surf Life Saving Queensland gives this advice. Adults and lifeguards follow it.
First, pour vinegar over the sting for at least 30 seconds. It stops any stinging cells that have not fired yet. Then pick off any tentacles with care.
If the person stops breathing, start CPR at once. Call the emergency number, which is 000 in Australia. Get a lifeguard if one is near.
There is an antivenom for Chironex fleckeri stings. Hospitals and ambulance stations keep it where the jellyfish live.
The tiny Irukandji
Not every dangerous box jellyfish is big. The Irukandji are tiny ones. Some are no bigger than a fingernail. They live in the same tropical waters off northern Australia.
Their sting may hardly be felt at first. Then, 5 to 40 minutes later, it can bring bad muscle pain, headache, sickness and sweating. Anyone who may have been stung needs watching for 45 minutes. They also need medical help.
The tiny Irukandji
- How small can some Irukandji jellyfish be?
- How long should someone who may have been stung by an Irukandji be watched?
The life of a box jellyfish
Box jellyfish start life as tiny blobs called polyps. These cling to rocks and other surfaces in shallow water.
Each polyp grows and then turns into one young jellyfish, which swims away. It grows up into an adult with a full box-shaped bell and long tentacles.
Box jellyfish and learning
Box jellyfish are good animals to study. Scientists want to understand their eyes and their venom. They also want to know how they live with no brain.
Maybe you are a student thinking, “What facts can help me to do my coursework on sea creatures?” The trustworthy sources listed at the end of this guide are a great place to start.
And if you simply love the sea, you can bring it into your bedroom with jelly fish wallpapers and other ocean designs.
More ocean and animal facts
Box jellyfish share the seas with many other strange animals. You can read about one animal of the far north in our polar bear facts for kids.
Box jellyfish also turn up off warm American coasts. The deadly Australian kind does not live there. Read about one warm coastal state in our California facts for kids.
Three things people get wrong
Box jellyfish are not just drifting blobs. They swim at almost four knots, and they steer by eye.
Not all box jellyfish are deadly. There are about 50 species, and only a few, such as Chironex fleckeri, are dangerous to people.
Box jellyfish do not live everywhere. The deadliest kinds keep to the Indian and Pacific Oceans, above all off northern Australia.
Did you know? Box jellyfish have no brain like ours, yet some of their eyes are built like ours, with a lens, iris and retina.
Try it
Draw a box jellyfish: a square bell with clusters of long tentacles at each corner and small dots for eyes on each side. How many eyes can you fit on?
Knowledge check
How is a box jellyfish different from most jellyfish?
Show answer
It can swim and steer instead of just drifting, and it has eyes.
What are nematocysts?
Show answer
Tiny stinging cells on the tentacles that shoot out and inject venom.
Frequently asked questions
Why is it called a box jellyfish?
A box jellyfish is named after its bell, which is shaped like a cube or box. Clusters of tentacles trail from each of its four corners.
How dangerous is a box jellyfish?
Some box jellyfish are harmless. But Chironex fleckeri, from northern Australia, has very strong venom. Its sting can stop a person moving, and it can stop the heart within minutes.
Where do box jellyfish live?
Box jellyfish live in warm water near the coast, all over the world. The most dangerous kinds keep to the Indian and Pacific Oceans, above all off northern Australia.
Do box jellyfish have eyes?
Yes. Box jellyfish have clusters of eyes on each side of their bell, and some of the eyes have a lens, cornea, iris and retina.
Can box jellyfish swim?
Yes. Unlike most jellyfish, which drift, box jellyfish can swim by squeezing their bell, reaching speeds of almost four knots.
What should you do if someone is stung by a box jellyfish?
Pour vinegar on the sting for at least 30 seconds, then pick off any tentacles. Start CPR if the person stops breathing, call 000 in Australia and get a lifeguard. Antivenom is kept at hospitals.
Sources
- US National Ocean Service (NOAA): box jellyfish — body shape, stinging cells, the size of Chironex fleckeri, eyes, where they live, venom and swimming
- Encyclopaedia Britannica: box jellyfish — the number of species, bell and tentacle sizes, where they live, diet and the deadliest species
- Surf Life Saving Queensland: marine stingers — where box jellyfish are found, stinger season, sting symptoms, first aid and Irukandji
Box jellyfish final quiz
- About how many species of box jellyfish are there?
- How long can the tentacles of Chironex fleckeri grow?
- How wide can the bell of a box jellyfish be?
- Where do the most dangerous box jellyfish mainly live?
- Why is vinegar poured on a box jellyfish sting?
- Where is the antivenom for Chironex fleckeri stings kept?
- How does a box jellyfish start its life?
- What does each box jellyfish polyp turn into?
- What makes box jellyfish better hunters than most jellyfish?
- Does the deadly Australian box jellyfish live off warm American coasts?
