Jellyfish Advice and Information

The most common Mediterranean jellyfish, Pelagia Noctiluca. Photo by Hans Hillewaert.

The most common Mediterranean jellyfish, Pelagia Noctiluca, not dangerous but possesses an uncomfortable sting. Photo by Hans Hillewaert.

Jellyfish Facts

There are around two thousand species of Jellyfish in the world but less than one hundred are considered dangerous to human animals. They are not in fact fish but invertebrates with none of the organs we would associate with higher life forms.

Jellyfish eat mainly zooplankton and do so by capturing them with toxic tentacles which range from a few inches to a few hundred feet long. They travel around the oceans via self propulsion, tide and wind, in warm and cold waters alike.

The lack of a brain in your average jellyfish means that if stings you it really can’t help it – unless it’s Chironex Fleckeri (Box Jelly) which can control itself efficiently since it has four brains and multiple eyes.
When Jellies’ stinging cells (nematocysts) make contact with your skin they fire their poison into it via tiny harpoons.

The Box jelly species, known as Sea Wasps or Cubozoa (ie. cube shape), includes Irukandji as far as scientists are concerned, though laymen think of the Box jelly as the big one and Irukandji as the little ‘un. The biological names are: Chironex Fleckeri (the Box) and Carukia Barnesi (the Peanut)

Box Jellyfish (Toxic Boxes)

The Box Jelly (aka Sea Wasp or Chironex Fleckeri) are the most toxic creatures on Earth. They and 20 close relatives are found off the shores of Northern Australia, PNG, Malaysia, Indonesia, the Philippines, Thailand and Vietnam. This marine animal has a boxy bell head the size of a basket ball, 4 parallel brains (one on each corner), 24 eyes and 60 anuses! (says Dan Nilsson, a vision expert from the University of Lund in Sweden). Then there are 5,000 deadly stinging cells on each of its 10- 60, two metre long tentacles.

Some researchers believe that groups of Box Jellies deliberately herd small fish and crustaceans towards the shore in order to trap them, thus bringing them into contact with humans.
New Scientist magazine in 2003 revealed that Box jellies are not ‘dim-witted ocean drifters’ but ‘fast, active predators that hunt and kill with incredible speed and brutality.’

The Toxic Box is responsible for at least one death a year around Australia and has killed 67 people since records began in 1883, though the total is misleading since many deaths attributed to heart attacks or drowning could have been caused by toxic jellies.
Problem shores are usually signposted, and this is one serious bubblepack to be avoided at all costs – the most poisonous creature in the world.
The Box Jelly is mostly a problem from October – May.


• severe pain
• headache, nausea, vomiting, diarrhoea
• skin swelling/wounds/redness
• difficulty breathing, swallowing and speech
• shivering, sweating
• irregular pulse/heart failure

Stings treatment

• pour vinegar over tentacles. Urine does not work on the Box Jelly or Irukandji.
• lift off any tentacles with a stick or similar.
• use pressure-immobilisation on limbs if possible. i.e. quickly wrap a light bandage above and below the sting (if you can’t get two fingers under the bandage, it’s too tight).
• Immobilize/splint the stung area and keep it at heart level (gravity-neutral) if possible. Too high causes venom to travel to the heart, too low causes more swelling.
• Do not drink alcohol or take any medicine or food.
• seek medical treatment urgently or apply antivenom if available.


Irukandji (Carukia barnesi and several other unidentified species that produce Irukandji Syndrome) also lurks in the waters of Northern Australia, mostly near Cairns and the Great Barrier Reef. Irregular sea currents can easily move it to the shore.
Irukandji is extremely painful and occasionally deadly and has been seen as far south as Brisbane. It’s mostly a problem from November – May, but has been recorded in all months except July and August.

Symptoms (as little as 5 minutes after apparently mild stings)

• lower back pain, intense headache.
• muscle cramps and shooting pains, nausea, vomiting.
• catastrophically high blood pressure.
• restlessness and feeling of impending doom.
• death from heart failure or fluid on the lungs.


• pour vinegar over tentacles.
• lift off any tentacles with a stick or similar.
• compress the wound area with a bandage.
• take pain killers.
• get medical treatment as soon as possible.

Portuguese Man-of-War

Also known as the Blue-bottle or Hydrozoa to a scientist, this is a sail bearing, wind blown animal which travels the Atlantic, Pacific and Indian Oceans and may be blown inshore. The larger varieties may be occasionally fatal to humans but are not usually dangerous.


• lift off any tentacles with a stick or similar.
• apply an ice pack
• apply a local anaesthetic (sunburn cream/insect bite cream).

Avoiding Jellyfish Stings

• Take extreme precautions if you have an existing heart condition as Jellyfish deaths are normally attributed to cardiac arrest (or pulmonary congestion). You are in great danger from the Toxic Boxes’ venomous sting unless treated immediately as the pain is so excruciating that you may go into shock and drown before reaching the shore. So swim with a partner if possible.

• Avoid swimming in the October-May high-jelly season, especially in the seas north of Brisbane, in Northern Australia, and particularly around Cairns and the Whitsunday islands,, especially in calm waters near the mouths of rivers, estuaries and creeks following rain. Also beware around PNG, Malaysia, Indonesia, the Philippines, Thailand and Vietnam.

• Wetsuits or Lycra ‘stinger suits ‘ offer good protection especially the sophisticated models with hands, neck and head coverage. Feet may be covered by fins or swimming shoes. Pantyhose is also apparently effective as the stings don’t ‘fire’ unless they feel skin.

• Take notice of warnings! Bathing areas prone to toxic jellies may have safety signs.

• Keep your eyes peeled when swimming in areas where the more dangerous variety live tho’ your chances of seeing Irukandji are smaller than they are.

• Dead jellyfish on the shore may look like gelatinous blobs and they are, but while there is still moisture, there can be life in those old cells and you may be stung. Safety first! Don’t tread on them and don’t pick them up.

General Treatment

• rinse the area with sea water. Do not scrub or wash with fresh water which will aggravate the stinging cells. Do not pour sun lotion or spirit-based liquid on the area.
• deactivate remaining cells with a vinegar rinse before removing them, otherwise inactive namatocysts may be triggered. If no vinegar is available use urine – but NOT for Box jelly and Irukandji stings. Ask a mate for a golden shower! Really! Preferably male urine as it’s considered to be more sterile.
• lift off any remaining tentacles with a stick or similar.
• if cells still linger, dust with flour and carefully scrape off with a blunt knife.
• after all tentacle sections have gone, pain can be treated with a cold pack and/or a local anaesthetic such as a sunburn lotion or insect bite treatment that lists ‘…ocaine’ as an ingredient.
• if there is continued swelling, or itchiness, apply a light steroid cream e.g. Hydrocortisone eczema cream.
• if muscle spasms persist see a doctor.

The stings are painful and unpleasant but not generally life-threatening, unless a swimmer has a weak heart, a severe allergic reaction or panics on encountering a shoal of blobbies and drowns…

The cause of the Mediterranean stinger explosion is the usual suspect – global warming boosting water temperatures by a couple of degrees as well as increased pollution-derived nutrients and reduced cool freshwater entering from rivers. However, overfishing of anchovies (which compete with jellies for plankton salad), turtles and tuna fish (which eat jellies for dessert) has also aided the mauve climate avenger’s expansionist tendencies.


• do not swim or paddle in streams, lakes, ponds or in the sea near a river mouth if you’re in a croc zone, especially within 100kms (62mls) of the coast of northern Australia. You may be hot, and that creek may look cool and empty, but crocs are the kings of camouflage.

• if you’re camping in north Australia park your tent more than 50m from any water, don’t leave rubbish around, and don’t collect water from the same spot every day.

• do not dangle arms or legs in the water, however inviting it seems.

• if you see one keep at least thirty foot (10m) away on land; don’t tease them because they only look slow and lazy; only swim in areas posted as safe.

• if you hear hissing or crunching sounds in the undergrowth at night, leave immediately.

• a croc will launch itself out of water like a missile, with no warning, so keep yourself, children and dogs well away from the water’s edge in croc zones. Do not underestimate their ability to propel themselves far out of the water at speed.

• if you come across croc babies – croquettes – leave the area immediately, don’t play with them. Fun, yes, dangerous, yes.

• these animals are mostly nocturnal. You won’t see them, they’ll see you. Don’t swim after dusk.

Doctors in Queensland are successfully using magnesium sulphate in clinical trials to cure Irukandji syndrome.
They are also testing a compound that prevents stinger cells from firing which may be added to waterproof sunscreen in the not too distant future…