Research shows that 75% of potentially fatal stings from the jellyfish can be prevented by wearing a stinger suit which is not recognised as skin and thus keep the jellyfish from firing off their venom.

When you are swimming or diving in a new area always ask the locals or lifeguards. They should be able to tell you if there are any jellyfish around or a sudden influx of these creatures locally. They tend to be seasonal and come in swarms into swimming areas, or they arrive after a storm or strong onshore wind.

Bags of Venom

The way jellyfish feed is by enveloping their prey in their tentacles and paralysing them with "nematocysts", tiny bags full of venom on the tentacles. On contact with a fish or human skin they fire off, releasing the poison into whatever they are in contact with. If this happens to be you or a friend then you need to act quickly.

Treatment: Get out of the water as soon as you can and have someone help get any tentacles off your skin. They must first of all stop any remaining nematocysts from firing off and the best thing for this is ordinary household vinegar. Pour this over the area affected and on any remaining tentacles. If there is no vinegar handy then there are other fluids you can use, the best of which is urine, which may seem bizarre but has good medical grounding due to its relative warmth and acidity.

Having been doused in whatever liquid try to take off any remaining tentacles with gloved hands so you don't get stings on your fingers. Depending on what sort of jellyfish it was, appropriate action needs to be taken.

If you were hit in Eastern Australia by the deadly Box Jellyfish, you need to get some anti venom as soon as possible and go under medical supervision for a while. Fortunately most stings are not deadly, just really painful.

Take a simple analgesic such as Ibuprofen and apply some calamine lotion on the affected area twice a day. Finally, if you're diving remember to always look up when surfacing after a dive, as this is where most problems happen. Going up head first into a Portuguese Man-of-War is not the best way to enjoy the sea.

Irukandji jellyfish are tiny and extremely venomous jellyfish that are found the world over, and which cause symptoms collectively known as Irukandji syndrome. Its size is roughly no larger than a centimetre cubed.

Irukandji are usually found near the coast, attracted by the warmer water, but blooms have been seen as far as five kilometres offshore.

Its venom is very powerful, 100 times as potent as that of a cobra, and 1000 times as potent as that of a tarantula.

When properly treated, a single sting is normally not fatal, but two people in Australia are believed to have died from Irukandji stings in 2002, greatly increasing public awareness of Irukandji syndrome.

It is unknown how many other deaths from Irukandji syndrome have been wrongly attributed to other causes. It is also unknown which jellyfish species can cause Irukandji syndrome apart from Carukia barnesi and Malo kingi.

Irukandji syndrome is produced by a very small amount of venom and includes severe pains at various parts of the body (typically excruciating muscle cramps in the arms and legs, severe pain in the back and kidneys, a burning sensation of the skin and face), headaches, nausea, restlessness, sweating, vomiting, high heart rate and blood pressure, and psychological phenomena (such as the feeling of impending death).

The sting itself is only moderately irritating; the severe syndrome is delayed for 5–120 minutes (30 minutes on average). The symptoms may last from hours to several days, and victims usually require hospitalization. As with box jellyfish, vinegar will deactivate unfired nematocysts on the skin, but has no effect on the venom already in the body.

Treatment is symptomatic, with antihistamines and anti-hypertensive drugs used to control inflammation and hypertension and intravenous opiates, such as morphine and fentanyl, to control the pain.

http://en.wikipedia.org/wiki/Irukandji_jellyfish

Chironex fleckeri, commonly known as sea wasp, is an infamous lethally venomous species of Box jellyfish living in northern Australia's coastal waters. It is considered the most lethal jellyfish in the world because of the numerous incidents resulting in injury or death to humans.

The amount of venom in one animal is enough to kill 60 adult humans, about 70 children, or 87 babies.

Notorious for its dangerous sting, C. fleckeri has tentacles up to 3 metres (10 ft) long which are covered in thousands upon thousands of nematocysts which, on contact, release microscopic darts, each delivering an extremely powerful venom. Being stung invariably results in excruciating pain, and if the sting area is significant, an untreated victim may die in as little as 3 minutes.

Treatment: First aid consists of washing the sting area with vinegar, and in no circumstance should alcohol, alcohol-based lotions, or methylated spirits be applied. Cardiopulmonary resuscitation (CPR) may be required. Medical help should be sought as soon as possible after considering these needs.

http://en.wikipedia.org/wiki/Box_Jellyfish
http://en.wikipedia.org/wiki/Chironex_fleckeri
http://library.thinkquest.org/C007974/2_1box.htm

The Portuguese Man o' War (Physalia physalis), also known as the blue bubble, blue bottle, man-of-war, or the Portuguese man of war, is a jelly-like, marine invertebrate of the family Physaliidae.

The common name comes from a Portuguese war ship type of the 15th and 16th century, the man-of-war or caravel (in Portuguese, Caravela), which had triangular sails similar in outline to the bladder of the Portuguese Man o' War.

While the Portuguese Man o' War resembles a jellyfish, it is in fact a siphonophore: a colony of four kinds of minute, highly modified individuals, which are specialized polyps and medusoids.

The Portuguese Man o' War is infamous for having a painful sting, and for swarming in many hundreds. It is responsible for up to 10,000 stings in Australia each summer, particularly on the east coast, with some others occurring off the coast states of South Australia and Western Australia.

The stinging venom-filled nematocysts in the tentacles of the Portuguese Man o' War can paralyze small fish and other prey. Detached tentacles and dead specimens (including those which wash up on shore) can sting just as painfully as the live creature in the water, and may remain potent for hours or even days after the death of the creature or the detachment of the tentacle.

Stings usually cause severe pain to humans, leaving whip-like, red welts on the skin which normally last about 2–3 days after the initial sting, although the pain should subside after about 1 hour. However, the venom can travel to the lymph nodes and may cause, depending on the amount of venom, a more intense pain. A sting may lead to an allergic reaction.

There can also be serious effects, including fever, shock, and interference with heart and lung action. Stings may also cause death, although this is rare. Medical attention may be necessary, especially where pain persists or is intense, or there is an extreme reaction, or the rash worsens, or a feeling of overall illness develops, or a red streak develops between swollen lymph nodes and the sting, or if either area becomes red, warm and tender.

Treatment: Research suggests that in the normal course the best treatment for a Portuguese Man o' War sting is:

1. to avoid any further contact with the Portuguese Man o' War and to carefully remove any remnants of the creature from the skin (taking care not to touch them directly with fingers or any other part of the skin to avoid secondary stinging);

2. to then apply salt water to the affected area (not fresh water, which tends to make the affected area worse);

3. If eyes have been affected they should be irrigated with copious amounts of room temperature tap water for at least 15 minutes and if vision blurs, or the eyes continue to tear, hurt, swell, or are light sensitive after irrigating, or there is any concern, a doctor should be seen as soon as possible;

4. to follow up with the application of hot water (45°C/113°F) to the affected area, which eases the pain of a sting by denaturing the toxins.

5. Vinegar dousing has been shown to cause strengthening of nematocysts from the larger (P. physalis) man-of-war species (that is, increasing toxin delivery and worsening the symptoms) while in the case of nematocysts of the smaller species (which has less severe stings), vinegar has been confirmed to provoke hemorrhaging. Vinegar is therefore not recommended.

6. The Portuguese Man o' War is often confused with jellyfish by its victims, which may lead to improper treatment of stings, as the venom differs from that of true jellyfish.

   http://en.wikipedia.org/wiki/Portuguese_Man_o%27_War

Australia's jellyfish swarm out during the summer months from October to May. The 2001-2002 season has produced the highest number of Irukandji syndromes on record. In total 116 patients presented to the Cairns Base Hospital with Irukandji syndrome; this does not include those that presented to other hospitals or local doctors.
1. 20% occurred on the reef, the rest on beaches north and south of Cairns.

2. 22% were overseas tourists.

3. 70% were local residents and the remainder were either visiting Queenslanders or interstate visitors.

4. 24% of stings occurred on the hands, face, neck or feet, the remainder occurred on areas that potentially could have been protected by the currently available stinger suits.

5. Only 55% of patients had any effective first aid applied prior to arrival at the Emergency Department.

6. Helicopter retrieval was necessary in 12% of patients, while the rest either attended by ambulance or presented by themselves.

7. 20% had evidence of heart problems from the sting and of these 6 (5%) had demonstrable heart dysfunction (2 were severe). One patient died as a result of complications (intra cerebral haemorrhage).

8. 37% were discharged within 6 hours of presentation the remainder requiring admission.

9. 41% were discharged after 24 hours and the remainder either required heart monitoring or intensive care treatment (2).

Jellyfish in Thailand come from around mid May to end of October. Make sure you wear appropriate clothing. Kite pants and a rashy or a stinger suit should be enough to enjoy your swim.

From experience the jellyfish to avoid are:


1. Browny-red ones (all sizes)
   
2. White ones (only the really big ones, small ones are a different species and don't sting).
   

They will leave a burn like mark on the skin, some hurt more than others. If stung, do not rub with hand, this will spread any tentacle around. Pour soda water on area, to wash any jelly bits away. Then get a plant called "Morning Glory" and mix with vinegar. Hold this over the area for around half an hour. Any Thai will know what to do if you say "Mangopune", Thai for jellyfish.

Two foreign tourists were fatally stung while swimming in waters off Koh Pha Ngan.

An Australian man has died from multiple stings by a toxic jellyfish. He died before arriving at a beachside clinic after receiving massive stings to his legs while swimming off the island's Hat Rin beach. Officials said he suffered terrible pain from the stings which left large welt marks on his legs.

"The long tentacles wrapped around his legs three or four times each. It would have been an excruciating death," an official said.

A day later, a Moroccan woman died from similar stings to her legs after being taken by speedboat to Ban Don Inter Hospital on the nearby island of Koh Samui.

The deaths on the island, which is known for hosting all-night rave parties, have prompted local authorities to warn tourists against swimming in the sea during the monsoon season, when the deadly jellyfish are frequently washed toward the beach by rough seas.

Thai police stationed on the island have since been handing out leaflets warning visitors against swimming, especially in the latter part of the day and early evening. But officials said many of the travellers were disregarding the warnings. "There is a general culture on the island that all is OK," one official said.