Box Jellyfish

Q: How to identify Box Jellyfish?

Look for fins, arms, tentacles, shells and body symmetry. Underwater light shifts colors, so structure and markings usually matter more than shade. Sea Creature Identifier: upload a photo and compare the visible details.

Q: What does Box Jellyfish eat?

These predators hunt small fish and crustaceans, stinging them with venomous tentacles.

Q: What should you do if a box jellyfish stings you?

Get out of the water if it is safe and get help from an adult or lifesaver. If the sting is more than small and local, or the person feels unwell, call 000. In tropical Australia pour household vinegar on the sting for at least 30 seconds, then pick off tentacles. Start CPR if the person is unresponsive and not breathing normally. Use a cold pack for pain.

Q: Does vinegar help a box jellyfish sting?

Yes, in tropical Australia it is the recommended first aid. Vinegar stops unfired stinging cells left on the skin from firing. One lab study found vinegar may squeeze more venom from cells that have already fired, so the guideline notes the evidence is mixed, but it still advises vinegar for box jellyfish and Irukandji stings.

Q: When is box jellyfish season in Australia?

The risk is highest in the warmer months. Surf Life Saving Queensland says the season typically runs from November to May, and in the Northern Territory 92% of confirmed stings happened between 1 October and 1 June. Box jellyfish can turn up at other times too, so follow beach signs all year.

Q: How many eyes does a box jellyfish have?

24. They sit on 4 eye clubs (rhopalia), 6 on each, and come in 4 types. Two on each club have lenses and can form a rough image, which helps box jellyfish dodge obstacles and steer.

Q: Is a box jellyfish a real jellyfish?

Box jellyfish belong to their own class, the Cubozoa, with about 50 described species. They differ from other jellyfish in their box-shaped bell, active swimming and complex eyes. The Portuguese man o’ war is not a jellyfish at all but a siphonophore colony.

Q: Is there an antivenom for box jellyfish?

Yes. Hospitals and ambulances in tropical coastal Australia carry box jellyfish antivenom, made in sheep. How much it helps is still debated, so fast first aid and calling 000 remain the most important steps.

Q: Where do box jellyfish live?

Chironex fleckeri lives in shallow coastal waters of tropical Australia: north of Agnes Water in Queensland, all Northern Territory waters and Western Australia south to Exmouth. It is also reported from New Guinea and parts of South-East Asia. It is an inshore species, not found offshore around coral reefs.

Q: How big is a box jellyfish?

Big adults have a bell 20–30 cm across, and the largest reach about 38 cm. The tentacles can stretch to about 3 m. Newly formed medusae are only about 1.8 mm across.

Chironex fleckeri

The Australian box jellyfish or sea wasp, Chironex fleckeri, is a large box jellyfish (class Cubozoa) of shallow coastal waters in tropical northern Australia and nearby seas. Unlike most jellyfish it swims actively and steers with 24 eyes on 4 sensory clubs, hunting prawns and small fish with up to 17 tentacles on each corner. Its sting can be dangerous to people, so in stinger season swimmers follow lifesavers, beach signs and vinegar first aid.

Also known as Australian box jellyfish, Chironex, Marine Stinger

Box jellyfish abilities

2–3 bell pulses a second
It swims by squeezing its bell 2 to 3 times a second, pushing water out through a narrow skirt at the rim. Box jellyfish are known for swimming faster and more nimbly than other jellyfish.
- Unlike most jellyfish, box jellyfish swim actively, more like fish than drifting jelly.
- Small ones jet. Bigger ones flex the velarium skirt to row and jet at once.
- They turn by pushing water out unevenly, both while squeezing and while relaxing.
- In the lab, C. fleckeri swam away from dark objects.
Sources [6, 8, 10]
24 eyes of 4 types
Four eye clubs hang round the bell, each with 6 eyes. Two of each six have lenses, and together they help box jellyfish steer round obstacles and find the right place to live.
- The lenses are finely tuned and give a nearly sharp image, but the retina sits slightly out of focus, so the view is probably wide and blurry.
- Tests on two box jellyfish species suggest they see without colour, using a single light-sensing pigment.
- Chiropsella bronzie, an Australian relative, uses its eyes to dodge obstacles.
- Tripedalia cystophora, a small Caribbean box jellyfish, peers up through the water surface at the mangrove trees to stay near them. Whether C. fleckeri does the same has not been shown.
Sources [7, 8, 9, 15]
up to 3 m tentacle stretch
Its tentacles can shrink to about 10 cm or stretch to about 3 m, trailing from all 4 corners like a living fishing net.
- Each corner carries up to 17 tentacles, so a big adult can have dozens.
- In aquarium tanks with moving water, C. fleckeri spread its tentacles and caught live shrimp, prawns and fish.
- Tentacles are added as the jellyfish grows: a new medusa starts with just 1 per corner.
Tentacle length
Box jellyfish, stretchedup to 3 m
Box jellyfish, shrunk≈10 cm
Portuguese man o’ war (average)≈10 m
A man o’ war’s tentacles can reach 30 m. It is a drifting colony, not a box jellyfish.
Sources [1, 5, 10, 11, 16]
3 main groups of stinging cell
Look inside a tentacle and you find bands of stinging cells. Each is a capsule with a coiled thread that fires when touched and injects fast-acting venom into prey.
- C. fleckeri has 3 main groups of stinging cells. Big jellyfish carry more of the type thought to hold the venom that stops fish.
- Its venom quickly damages cells. In a 2019 study, scientists found a substance that blocked the venom in mice up to 15 minutes after exposure. Ideas like this are still being researched.
- Stinging cells can still work in loose tentacles or a dead jellyfish, so never touch one on the beach.
Sources [3, 11, 13, 17]
< 4 cm size that eats only prawns
Small box jellyfish eat prawns. As they grow they switch to fish, and their stinging cells change to match their new food.
- In one study, C. fleckeri under 40 mm across fed only on prawns, medium ones on fish and prawns, and large ones mostly on fish.
- It often moves from deeper water into the shallows to hunt small prawns.
- Once prey is stuck to the tentacles, the corner arms bend in and pass it to the mouth.
Sources [3, 10, 13]
1.8 mm size of a brand-new medusa
Before it can swim, a box jellyfish lives as a tiny polyp, thought to be hidden in estuaries. From about early September, polyps change into baby medusae just 1.8 mm across, which swim off and grow up to 3 mm a day.
- Across the seasons studied, the first polyps changed between 30 August and 5 September.
- After that, a few new medusae appeared almost every day, rather than all at once.
- In the population studied, they grew to about 19 cm across in under 3 months. The oldest were about 78 days old.
- Where exactly the polyps live in the wild is still not well known.
Sources [5]
up to 38 cm and still hard to spot
A big box jellyfish is almost completely transparent. People who are stung often never see it, which is why beach signs and lifesaver patrols matter.
- Even a bell the size of a football is very hard to see in the water.
- Scientists tested drones to count them. Bigger jellyfish and cloudy skies made them easier to detect. Wind and water clarity also mattered.
- That is why beach signs, lifesaver patrols and stinger-season rules matter even when the water looks empty.
Sources [1, 3, 18]

Tap a pin on the model or a part below.

up to 38 cm across the bell
- The bell is box-shaped, with 4 flat sides, and almost transparent, so it is very hard to see in the water.
- Most big adults measure 20–30 cm across. Surf Life Saving Queensland gives up to 38 cm for the largest.
- It is the largest box jellyfish: a review reports that the biggest can weigh up to 6 kg.
- Young medusae grow fast: up to 3 mm wider every day.
Sources [1, 2, 3, 4, 5]
2–3 pulses a second
- A thin, flexible shelf of tissue round the bell opening, the velarium, speeds up the water pushed out with each squeeze.
- Small box jellyfish swim mainly by jet propulsion. Big ones bend the velarium to row and jet at the same time.
- By squeezing unevenly they can turn while the bell contracts and while it relaxes.
Sources [6]
24 eyes on 4 clubs
- Each side of the bell has a sensory club called a rhopalium, carrying 6 eyes of 4 different types.
- Two eyes on each club have real lenses, like tiny camera eyes.
- In the Caribbean box jellyfish Tripedalia, each club hangs so that its upper lens eye always looks straight up, whichever way the jellyfish tilts.
- Each club also holds a crystal, the statolith. Its daily growth rings let scientists work out a jellyfish’s age.
Sources [5, 7, 8, 9]
- The mouth sits at the end of a short tube, the manubrium, hanging inside the bell.
- The corner arms bend inwards to bring caught prey up to the mouth.
- Digestion is fast. Bell contractions pump the food through canals that spread it round the body.
Sources [10]
- The swimming medusa is the stage that makes eggs or sperm. The tiny polyp stage reproduces without a partner.
- In one study, medusae in estuaries were bigger on average than those along open beaches.
- Medusae live for only one season: the oldest found were about 78 days old.
Sources [5]
4 arms, one per corner
- Each corner of the bell has a fleshy arm called a pedalium, and the tentacles grow from it.
- Flexing these arms inwards brings prey caught on the tentacles up to the mouth.
- A brand-new medusa has 1 tentacle on each arm and adds more as it grows.
- Scientists measure box jellyfish across the bell from one corner arm to the opposite one.
Sources [4, 5, 10]
up to 3 m when stretched out
- Up to 17 ribbon-like tentacles hang from each corner. Older sources often say 15.
- They can shrink to about 10 cm or stretch out to about 3 m.
- They are covered in stinging cells that fire on contact.
Sources [1, 4, 11]
3 main groups of stinging cell
- Stinging cells (nematocysts) are tiny capsules with a coiled, hollow thread that shoots out on touch and injects venom.
- As C. fleckeri grows, a larger share of its stinging cells are the type thought to carry the venom that stops fish.
- Vinegar stops unfired stinging cells from firing, which is why it is used in tropical Australian first aid.
Sources [2, 3, 12, 13, 14]

Real box jellyfish and their relatives

Photos from Wikimedia Commons. Free photos of C. fleckeri itself are rare, so some show close relatives, as labelled.

Chironex yamaguchii, a close relative of the Australian box jellyfish, at Enoshima Aquarium, JapanPhoto: Totti, CC BY-SA 4.0
Another view of Chironex yamaguchii, which shares the box shape and corner tentacles of C. fleckeriPhoto: Totti, CC BY-SA 4.0
Stinging cells (nematocysts) from Chironex fleckeri tentacles, magnified 400 timesPhoto: Brinkman DL, Aziz A, Loukas A, Potriquet J, Seymour J, Mulvenna J, CC BY-SA 3.0
An eye club (rhopalium, in red) on Tripedalia cystophora, a small Caribbean box jellyfishPhoto: Jan Bielecki, Alexander K. Zaharoff et al., CC BY 4.0
The box jellyfish visual system: 4 eye clubs, each with 6 eyes of 4 typesPhoto: Jan Bielecki, Alexander K. Zaharoff et al., CC BY 4.0
Tripedalia cystophora, the box jellyfish that steers by mangrove trees seen through the water surfacePhoto: Jan Bielecki, Alexander K. Zaharoff et al., CC BY-SA 4.0
Irukandji (Carukia barnesi)A different box jellyfish, only 1–2 cm across, with just 4 tentacles, one per corner. Its sting can cause Irukandji syndrome.Young ones eat small invertebrates; adults catch fishCarukia barnesi, the tiny Irukandji jellyfish. Photo: Lisa-ann Gershwin, CC BY 4.0
Irukandji (Carukia barnesi)A different box jellyfish, only 1–2 cm across, with just 4 tentacles, one per corner. Its sting can cause Irukandji syndrome.Young ones eat small invertebrates; adults catch fishAn Irukandji jellyfish from Queensland, Australia. Photo: GondwanaGirl, CC BY-SA 3.0
A marine stinger net at Ellis Beach, near Cairns, QueenslandPhoto: Kerry Raymond, CC BY 4.0
An Australian beach sign about hazardous marine creaturesPhoto: Genet, CC BY-SA 4.0

Box jellyfish by the numbers

Measured by scientists and lifesaving services, with comparisons you can picture.

Bell width: up to 38 cm; most big adults are 20–30 cm across⁠[1, 2]
Tentacle length: up to 3 m; shrinks to about 10 cm while swimming; Stretched out, about 30 times its shrunk length⁠[1, 11]
Tentacles per corner: up to 17; on each of the 4 corner arms⁠[1, 4]
Eyes: 24; 6 on each of 4 eye clubs, of 4 types⁠[7]
Bell pulses: 2–3 a second; smaller ones pulse faster⁠[6]
Growth: up to 3 mm a day; to about 19 cm across in a season; About 2 cm wider every week⁠[5]
Brand-new medusa: 1.8 mm; across, just after it leaves the polyp⁠[5]
Medusa lifespan: ≈78 days; the oldest medusae found in one long-term study⁠[5]
Main stinger season: Oct–Jun; 92% of confirmed stings in the Top End fell between 1 October and 1 June⁠[21]
Box jellyfish species: ≈50; described species in the class Cubozoa⁠[22]

Box jellyfish myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“Weeing on a jellyfish sting helps.”
“A box jellyfish washed up on the beach can’t sting.”
“Rinse a box jellyfish sting with fresh water.”
“Vinegar is the right first aid for every jellyfish sting.”
“Box jellyfish just drift wherever the current takes them.”
“Box jellyfish have 24 eyes.”
“Some sea turtles eat box jellyfish.”
“Most box jellyfish stings are deadly.”

Box jellyfish safety: what to do

Box jellyfish stings are painful and can be serious, but simple steps make beaches safer. This follows Australia’s first-aid guideline (ANZCOR) and Surf Life Saving Queensland.

000
call for help
Get the person out of the water if it is safe. If they have more than a small local sting, or look or feel unwell, call 000 for an ambulance and get a lifesaver. Start CPR if they are unresponsive and not breathing normally.⁠[2, 1]
30 s
of vinegar
In tropical Australia, pour household vinegar over the sting for at least 30 seconds, then pick off any tentacles. Vinegar stops unfired stinging cells. Don’t use it on bluebottle stings.⁠[2, 1, 14]
Sea water
not fresh water
No vinegar? Pick off the tentacles (this does not harm the person helping) and rinse well with sea water. Fresh water can make stinging cells fire. Don’t rub the sting.⁠[2, 1]
Ice
for the pain
A cold pack or ice in a dry plastic bag can ease the pain. Stay with the person and watch them until help arrives. Hospitals and ambulances in tropical coastal areas carry box jellyfish antivenom.⁠[2, 1]
Nov–May
riskiest months in Queensland
Stingers can turn up in any month in the tropics, but the risk is highest in the warmer months. Swim at patrolled beaches, follow the lifesavers and obey the signs.⁠[1, 23, 3]
83%
of stings in shallow water
In a Northern Territory study, most confirmed stings happened in water 1 m deep or less, often in the late afternoon on calm days. Shallow water is not automatically safe in stinger season.⁠[21]
4
deaths in 18 years
Australia records about 40,000 jellyfish stings a year, from many species. Between 2004 and 2022, 4 people died from jellyfish stings. Most box jellyfish stings are not life-threatening.⁠[2, 21]

General information, not medical advice. In an emergency in Australia, call 000.

Box jellyfish records

Superlatives and record holders, each checked against its source.

Largest box jellyfish
bell up to 38 cm
Chironex fleckeri
Called the largest of the box jellyfish; reported up to 6 kg.⁠[4, 1, 3]
Most complex eyes of any jellyfish
24 eyes, 4 types
Box jellyfish (Cubozoa)
No other cnidarians have such an elaborate set of senses, including image-forming eyes that evolved separately from ours.⁠[7, 8, 24]
Most advanced lenses in a simple animal
nearly aberration-free
Box jellyfish lens eyes (studied in Tripedalia cystophora)
Such finely tuned lenses were previously known only from a few advanced animal groups.⁠[8]
Nimblest jellyfish swimmers
2–3 pulses a second
Box jellyfish (cubomedusae)
Unusual among jellyfish for their swimming speed and manoeuvrability.⁠[6]

Life of a box jellyfish

One year in the life of Chironex fleckeri in tropical Australia, from polyp to adult.

All year
Polyps wait
Tiny polyps live fixed in one place, probably in estuaries, and multiply without a partner.⁠[5]
Early September
First medusae
Polyps start changing into medusae between about 30 August and 5 September, and keep releasing a few every day.⁠[5]
Day 1
Tiny swimmer
A new medusa is about 1.8 mm across with 1 tentacle on each corner.⁠[5]
September–November
Prawn hunter
It grows up to 3 mm a day. While under about 4 cm, it eats only prawns.⁠[5, 13]
October–December
Stinger season begins
Medusae reach the beaches. In far north Queensland they usually arrive in December, sometimes as early as October.⁠[5, 21]
Summer
Fish hunter
Now bigger, with more tentacles, it hunts mostly fish. Estuaries tend to hold the biggest ones.⁠[13, 5]
May–June
Season ends
The stinger season fades out. Medusae are the stage that makes eggs and sperm, and they live only a few months: the oldest found were about 78 days old.⁠[5, 21, 18]

Box jellyfish vs Irukandji vs Portuguese man o’ war

Three stingers people often mix up. Only two of them are box jellyfish, and the man o’ war isn’t a jellyfish at all.

Box jellyfish (Chironex fleckeri) vs Irukandji (Carukia barnesi) vs Portuguese man o’ war (Physalia physalis)
	Box jellyfish	Irukandji	Portuguese man o’ war
Scientific name⁠[25, 19, 26]	Chironex fleckeri	Carukia barnesi	Physalia physalis
What it is⁠[25, 19, 16, 3]	A box jellyfish (class Cubozoa)	A box jellyfish (class Cubozoa)	A siphonophore: a colony of many linked individuals, not a true jellyfish
Body size⁠[1, 3]	Bell up to 38 cm	Bell 1–2 cm	Gas float 2–25 cm long
Tentacles⁠[1, 2, 16]	Up to 17 per corner, up to 3 m long	4, one per corner	Many, about 10 m on average, up to 30 m
How it moves⁠[6, 8, 16]	Swims by pulsing its bell	Swims by pulsing its bell	Drifts with wind and currents
The sting⁠[2, 1]	Severe pain at once, whip-like marks	Often a minor sting; whole-body symptoms 5–40 minutes later	Immediate pain; blue tentacles often stuck to skin
First aid in Australia⁠[2, 1]	Call 000, vinegar 30 s, then remove tentacles	Call 000, vinegar 30 s	No vinegar: remove tentacles, rinse with sea water, hot water for pain

In Australia the bluebottle is a Physalia too. All three can sting even when washed up.

Is the box jellyfish endangered?

Nobody has assessed Chironex fleckeri for the IUCN Red List. It is common in its tropical range in season, but scientists still know little about how many there are.

IUCN Red List

Not Evaluated (NE)

Trend unknown

No Red List assessment exists, so its population trend is unknown.⁠[27]

Not evaluated by the IUCN Red List (checked October 2026)

Threats

Unknown numbers
Basic facts such as how many box jellyfish there are and how this changes between years are still poorly known.⁠[18]
Hidden polyps
The polyps are thought to live in estuaries, but where exactly is unclear, so it is hard to know how changes to estuaries might affect them.⁠[5]

What’s helping

Drone surveys
Scientists in Queensland tested drones to spot box jellyfish from the air, a safer way to count them.⁠[18]
Reading balance stones
Daily rings in the statoliths reveal each jellyfish’s age, showing when seasons start and how fast the animals grow.⁠[5]
Venom research
Studying the venom has led to new ideas for treating stings, such as a substance that blocked the venom in mice.⁠[11]

Relatives

Irukandji (Carukia barnesi)Not Evaluated
A tiny Australian box jellyfish, also not assessed by the IUCN.⁠[28, 1]

Box jellyfish quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

How many eyes does a box jellyfish have?

Box Jellyfish field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

These predators hunt small fish and crustaceans, stinging them with venomous tentacles.

Primary Foods

small fish
prawns
shrimp
small crustaceans
Foraging Method: Foraging

Age differences: Small box jellyfish (under about 4 cm across) eat only prawns. As they grow, they switch to fish.

Ecological connections

Green Sea TurtleEaten by
Scientists have seen green turtles eating Box Jellyfish in the wild.
PrawnsEats
Small box jellyfish eat prawns, then switch to fish as they grow.

Safety

Danger 5/5 · Extreme

Never touch a Box Jellyfish, even one washed up on the beach: it can still sting. Swim only at patrolled beaches, follow the signs and lifesavers, and tell an adult or lifesaver if you see one.

Traits

Collections

Invertebrates

Classification

Kingdom: Animalia
Phylum: Cnidaria
Class: Cubozoa
Order: Chirodropida
Family: Chirodropidae
Genus: Chironex

Also known as

Australian box jellyfish · Chironex · Marine Stinger · Sea Wasp

Sources for these box jellyfish facts

29 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Box Jellyfish?

Look for fins, arms, tentacles, shells and body symmetry. Underwater light shifts colors, so structure and markings usually matter more than shade. Sea Creature Identifier: upload a photo and compare the visible details.

How long is Box Jellyfish?

30 cm

How big is Box Jellyfish?

300 cm

How long does Box Jellyfish live?

1 years

What does Box Jellyfish eat?

These predators hunt small fish and crustaceans, stinging them with venomous tentacles.

Where is Box Jellyfish usually found?

Shallow coastal waters

How does Box Jellyfish hunt?

Foraging

What should you do if a box jellyfish stings you?

Get out of the water if it is safe and get help from an adult or lifesaver. If the sting is more than small and local, or the person feels unwell, call 000. In tropical Australia pour household vinegar on the sting for at least 30 seconds, then pick off tentacles. Start CPR if the person is unresponsive and not breathing normally. Use a cold pack for pain.

Does vinegar help a box jellyfish sting?

Yes, in tropical Australia it is the recommended first aid. Vinegar stops unfired stinging cells left on the skin from firing. One lab study found vinegar may squeeze more venom from cells that have already fired, so the guideline notes the evidence is mixed, but it still advises vinegar for box jellyfish and Irukandji stings.

When is box jellyfish season in Australia?

The risk is highest in the warmer months. Surf Life Saving Queensland says the season typically runs from November to May, and in the Northern Territory 92% of confirmed stings happened between 1 October and 1 June. Box jellyfish can turn up at other times too, so follow beach signs all year.

How many eyes does a box jellyfish have?

24. They sit on 4 eye clubs (rhopalia), 6 on each, and come in 4 types. Two on each club have lenses and can form a rough image, which helps box jellyfish dodge obstacles and steer.

Is a box jellyfish a real jellyfish?

Box jellyfish belong to their own class, the Cubozoa, with about 50 described species. They differ from other jellyfish in their box-shaped bell, active swimming and complex eyes. The Portuguese man o’ war is not a jellyfish at all but a siphonophore colony.

Is there an antivenom for box jellyfish?

Yes. Hospitals and ambulances in tropical coastal Australia carry box jellyfish antivenom, made in sheep. How much it helps is still debated, so fast first aid and calling 000 remain the most important steps.

Where do box jellyfish live?

Chironex fleckeri lives in shallow coastal waters of tropical Australia: north of Agnes Water in Queensland, all Northern Territory waters and Western Australia south to Exmouth. It is also reported from New Guinea and parts of South-East Asia. It is an inshore species, not found offshore around coral reefs.

How big is a box jellyfish?

Big adults have a bell 20–30 cm across, and the largest reach about 38 cm. The tentacles can stretch to about 3 m. Newly formed medusae are only about 1.8 mm across.