The Pacific Ocean contains some of the most dangerous jellyfish in the world such as the Portuguese man-of-war and the sea wasp. The best protection against these organisms is adequate skin diving clothing. The most effective treatment for stings is white vinegar, but cortisone also has some effect.

Divers come in contact with many types of stinging sea animals. In the South Pacific, some of these animals can be dangerous. Along Australia’s Queensland Coast for instance, there is the Sea Wasp (Chironex flecken), a dangerous jellyfish that can kill those who contact it.


All stinging jellyfish, corals and marine animals can release millions of capsules called nematocysts. These small structures contain a “dart” with a toxin that is released when the nematocyst is stimulated. Contact with a jellyfish tentacle causes many millions of nematocysts to be deposited on the skin. They are not all stimulated to inject the dart at the same time. Many nematocysts remain on the skin to be activated by contact later. Consequently, contact with a nematocyst-bearing animal produces an initial sting that is often followed by continuous stings. The initial contact is usually the worst because it triggers many nematocysts to inject their toxin. In the case of a Sea Wasp, the initial dose can be lethal.


The Sea Wasp is described as a box jellyfish (cubomedusa) because it is square, with one or two tentacles at each corner. Sea Wasp venom affects the nerves, heart and blood cells and causes damage to the skin in the contact area. Sea Wasp stings can cause respiratory paralysis but a victim can be saved by mouth to mouth respiration. The venom breaks down rapidly in the body, usually lasting no more than 30 minutes. If respiration can be supported that long, the victim will survive. Following contact, a severe blistering rash will occur that produces permanent scarring.

Sea Wasp Jellyfish

When a swimmer is injured by a Sea Wasp, there is usually time for him/her to get to the beach and get help. A diver in deeper water is in more danger because breathing paralysis will result in drowning if assistance is not provided. In Australia, an antivenin for the Sea Wasp sting is available in hospitals. Another Australian box jellyfish, the Morbakka, also produces severe stings but is not as dangerous as the Sea Wasp.


Other toxic jellyfish found in the waters around Australia cause what is known as the Irukandji Sting Syndrome. Fifteen to 30 minutes after contact with the jellyfish there is intense, cramp-like pain in the area of the sting and blood pressure rises. Accompanying symptoms include headache, cold extremities and reduced urine output, suggestive of a massive adrenaline release caused by the toxin. Early recognition of this type of sting is difficult because the pain and skin reaction are minor.


Portuguese Man of War jellyfish are common in most warm seas of the world. They drift on the surface, driven by the wind blowing against the bright blue inflated sail that also serves as a float. Beneath the blue sail is a cluster of tentacles that can be 20 to 30 feet long. These trail beneath and below the sail to sting small fish that wander into them. Swimmers and divers can also swim into the long streamers trailing below the sail. Contact with a tentacle causes severe pain and skin injury. There have been several deaths from the Portuguese Man of War. The toxin can cause respiratory paralysis but often death is owing to effects of the toxin on another illness, such as heart disease, that is aggravated by the toxin. Contact with a small portion of tentacle (probably millions of nematocysts) will cause a severe skin reaction but the toxin dose is usually not enough to threaten life in a healthy diver or swimmer. Massive contact, however, can cause serious illness or death. Children who receive a large toxin dose are particularly at risk.


Contact with most other species of jellyfish will not cause a serious problem, The sting of most jellyfish is annoying and can produce mild or moderate skin responses that usually heal without permanent scarring. This same effect is true for other nematocyst bearing animals such as fire coral, stinging hydroids, hard and soft corals and anemones.


Stings can be prevented by wearing protective clothing, Lycra/nylon dive suits provide excellent protection. Gloves should be worn to protect the hands from corals and other stinging animals. The thickness of the covering needs to be about the same as nylon stockings.

Many of the stinging jellyfish swim near the surface at night. On night dives, don’t linger near the surface. Search the water with your light for these small, transparent jellyfish. The box jellyfish of the Caribbean does produce a severe sting but it is not life threatening. Caution is still worthwhile.

Treatment of the local sting involves destroying the untriggered nematocysts. Over the years, ammonia solution, meat tenderizer, rubbing of sand, fresh water and urine have been recommended. Sand and fresh water both trigger the nematocysts so, if you want an extra thrill from your jellyfish contact, sand and fresh water will produce extra stings. Present advice is to use plain white vinegar to destroy the nematocysts on the skin. Severe reactions have been treated with cortisone with some success.

Remember: Tentacles contain active nematocysts even when detached from the jellyfish. Contact with nematocysts attached to a diving suit can cause stings several hours after leaving the water.

Although most sea stings are bothersome but not dangerous, divers should avoid contact with stinging animals to minimize injury to the skin and eliminate the possibility of serious injury.


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