The Australian Box Jellyfish
An Exceptionally Lethal Creature, also known as
Boxfish, Sea Wasp, Fire Medusa, Or Just Stinger

The Indo-Pacific or Australian box jellyfish (Chironex Fleckeri) is claimed to be the most venomous marine animal known to mankind and its sting is often fatal.

This extremely poisonous marine stinger frequents Australia's northern oceans all year round.

However, it is particularly dangerous during the wet season, from about November to April.

This page will tell you more about the Australian Box Jellyfish: what does it look like, where does it live, and how painful or dangerous is a Box Jellyfish sting? (Very!)

Facts | Habitat,Life Cycle,Food | Stinger Season | The Venom | First Aid

Box Jellyfish Facts

  • Box jellyfish belong to the class Cubozoa, and are not a true jellyfish (Scyphozoa), although they show many similar characteristics.
  • The bell or cube shaped jellyfish has four distinct sides, hence the box in the name.
  • When people talk about the extremely dangerous Australian box jellyfish they refer to the species Chironex fleckeri. This is the largest box jellyfish species.
  • The other species that is known to have caused deaths is Carukia barnesi, commonly called Irukandji. This one is a tiny jellyfish, only about thumbnail size. I talk about Irukandji here.
  • There are other species and not all are poisonous. (From here on, if I say box jellyfish, I am referring to Chironex fleckeri.)
  • A fully grown box jellyfish has a respectable size: it measures up to 20cm along each box side (or 30 cm in diameter), and the tentacles can grow up to 3 metres in length. Its weight can reach 2 kg.
  • There are about 15 tentacles on each corner, and each tentacle has many thousand stinging cells (nematocysts). The stinging cells are activated by contact with certain chemicals on the surface of fish, shellfish or humans.
  • Box jellyfish are transparent and pale blue in colour, which makes them pretty much invisible in the water. So much so that for years nobody knew what was causing swimmers such excruciating pain, and sometimes killed them.
  • The box jellyfish propels itself forward in a jet like motion and can reach three to four knots, that's 1.5 to 2 metres per second. (True jellyfish in contrast rather drift.)
  • Box jellyfish can see. They have clusters of eyes on each side of the box. Some of those eyes are surprisingly sophisticated, with a lens and cornea, an iris that can contract in bright light, and a retina.
  • Their speed and vision leads some researchers to believe that box jellyfish actively hunt their prey, others insist they are passive opportunists, meaning they just hang around and wait for prey to bump into their tentacles. They certainly are very good at avoiding even tiny objects and probably at least try to avoid humans, too.
  • Box jellyfish venom is very different from the venom of the true jellyfish. More on the venom and its effects below.
  • Chironex fleckeri have caused at least 63 deaths in Australia since 1884. (Irukandji caused two that we know of.)

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Box Jellyfish Habitat, Life Cycle And Food

The Australian box jellyfish is found in the tropical oceans around northern Australia. Their habitat extends as far south as Exmouth on the west coast, and Bustard Heads on the east coast (just north of Agnes Waters). Chironex fleckeri is also present in the waters of the Indo-Pacific region near Papua New Guinea, the Phillipines and Vietnam. Their exact distribution hasn't been determined yet.

Box Jellyfish like to hang around river mouths, estuaries and creeks, especially after rain. When the tide is rising they tend to move towards shallower waters. What they don't like are deep waters and rough seas. They are also absent over coral reefs, and over areas that have lots of seagrass or weed.

In late summer the adult jellyfish spawn at the river mouths. The eggs, once fertilised, turn into tiny polyps that attach themselves to rocks where they develop until next spring. Spring sees the polyps turn into tiny jellyfish that are washed downstream with the summer rains.

Box Jellyfish eat small fish and crustaceans. If you picture a tiny jellyfish struggling with a shrimp you may imagine how easy it would be for the shrimp to tear the jellyfish. That's why the jellyfish developed that very potent venom, they need to kill the shrimp instantly...

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The Box Jellyfish Season

It's hard to give a general answer as to when exactly the stinger season starts and ends, the general rule says wet season is stinger season, and that's from October/November to April/May.

Closer to the equator they are found earlier in the year than in the tropics. Smaller stingers appear every year in Darwin in August! They are only half the size of the large ones found in Queensland, and nobody knows why.

The largest specimen are usually found towards the end of the season, but for no particular reason in some years there may be large specimen in some locations early in the season.

You also can't count on the season ending in April/May. Especially in the southern parts you may encounter stingers well into June.

Box Jellyfish stings have been reported in all months in the Northern Territory, and in all months but June and July in Queensland!

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The Box Jellyfish Sting And Venom

Stings of Chironex fleckeri have several very severe consequences, due to its cardiotoxic (effect on the heart), neurotoxic (damage to the nerves) and dermatonecrotic (effect on the skin) components.

What does that mean? To start with it is not uncommon for victims who have had extensive contact (three metres of tentacles touching the skin can be enough to be fatal) to experience cardiac arrest within minutes.

Even if that is not the case the pain from a sting is so excruciating and overwhelming that a victim can immediately go into shock, fatal if the victim is swimming alone. Someone stung while swimming will rarely be able to make it back to shore on their own.

The tentacles stick tightly to the skin and may continue to release venom if not treated correctly, making things worse. Severe stings can lead to necrosis of the affected tissue (which means it gets eaten away...), which is where the nasty scars come from.

The severity of a sting depends on the size of the box jellyfish, the amount of tentacles involved, the size of the victim (children are obviously more vulnerable), but also on the sensitivity of the skin of the victim.

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First Aid For Box Jellyfish Stings

The Chironex fleckeri venom is so potent that in severe cases victims can quickly go into cardiac arrest! If that's the case obviously CPR (cardio pulmonary resuscitation) takes priority over everything else.

Luckily it's not always that bad. It depends where the tentacles touched (across the chest is obviously a lot more dangerous than on the ankle), and how much venom was released.

Usually the most important thing to do first is to inactivate the remaining stinging cells. This should be done by pouring normal vinegar over the tentacles (soak for at least 30 seconds). Only then can the tentacles be removed, otherwise you will cause more venom to be released.

Many popular Australian beaches where box jellyfish are present will even have a bottle of vinegar stored on the beach next to the warning signs. Ordinary vinegar has saved dozens of lives of unfortunate swimmers and there is no other first aid remedy that is recommended, despite what you may read elsewhere (methylated spirits, ammonia, urine, bicarbonate soda and what not...). A bottle of vinegar is certainly a useful addition to your first aid kit.

In mild cases the effects of the venom can be managed with ice, painkillers and antihistamins. More serious cases will likely require treatment of the systemic symptoms, and that means antivenin. All ambulances, hospitals and medical centres in box jellyfish areas will carry the antivenin, as in serious cases it needs to be given within minutes! Early administration of the antivenom can relieve the pain and may also reduce scarring.

The need for antivenom is indicated by cardio-respiratory arrest (obviously, but then it's often too late to reverse the effects of the venom), irregular heartbeat, difficulty breathing or swallowing and by extensive skin damage (which indicates the release of a great amount of venom).

If there is no help nearby then a pressure immobilisation bandage as described for snake bites should be applied and the patient transported to the next medical centre as quickly as possible.

Edit: Pressure bandages are no longer recommended! Research showed that using bandages caused additional venom discharge, despite the use of vinegar.

Note: there is no antivenom for Irukandji!

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Dangerous Australian Animals

Read about other Australian Animals

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