There are almost 200 known species of jellyfish drifting through our planet’s seas, all of which contain venomous stinging cells, but only a few of which can have serious consequences for humans. While many of these species are found within specific regions that may be nowhere near your home, it will hurt less to learn about these species than to come into contact with one and not know what’s happening to you. If nothing more, this article will make a great case for always wearing exposure protection while snorkeling and SCUBA diving, even in warm water! Due to the severe health risks an encounter with these species pose to humans, victims should always seek immediate medical treatment in the event of sting.
Chironex fleckeri, commonly known as a sea wasp, is our top venomous jellyfish not just because of its lethal poison, but because this species is nearly invisible and prefers shallow water, putting them in direct contact with swimmers enjoying the beach. Its venom is thought to be the strongest of any species on Earth, not just jellyfish, with the ability to kill an adult man with a dose of venom that weighs about as much as a single grain of salt. Sixty-three human deaths were attributed to the sea wasp over the course of 80 years in Australia — and those are just the known cases.
This species is a smaller version of the Chironex fleckeri, but despite its diminutive size, this jellyfish packs quite a wallop. Located in the waters of the Indo-Pacific and the Western Atlantic Oceans, they are known as “habu” in Japan’s Okinawa Prefecture, where encounters between people and this species occur annually. The sting is very painful, and in extreme cases can cause cardiac arrest. Chiropsalmus quadrigatus is distinguished by one hand-like appendage on all four sides of its bell, each of which have eight long, flat tentacles that scientists believe are more suited to catching fish, rather than the crustaceans and other jellies that are the prey of round-tentacled species.
The tiny Irukandji is another jellyfish that is not playing around when it comes to its venomous sting. Scientists once believed this species to be found only in Australian waters, but recent research by National Geographic has recorded their presence from Florida to Japan to the British Isles, meaning a lot more research remains to be done on this tiny killer. Its small size — about the size of an adult fingernail — and nearly transparent body makes it an incredible threat to humans, who will in most cases feel the burn without ever having seen their attacker. A sting from the Irukandji produces what is known as Irukandji Syndrome, in which the victim will feel severe pain in the back and kidneys, burning sensation of the skin, and excruciating muscle cramping in the legs and arms.
Morbakka fenneri, known familiarly as the fire jellyfish for its potent sting, lives in the calm waterways and marinas off the coast of Queensland, preferring the warmer waters of the north. Morbakka fenneriare is a bit larger than the other jellyfish on this list, measuring roughly four inches in length with a two-inch bell diameter, and a solid body with bright pink wart-like protrusions on the top. Their somewhat more visible size means that most people who catch a sting can usually locate the source nearby. While the stings are indeed painful, they are not typically life-threatening.
Alatina alata (up until recently known as Carybdea alata) is the last on our list of venomous jellyfish, known for swarming off the coasts and bay areas of Hawaii and other parts of the Pacific, as well as along the beaches of Pakistan in the Arabian Sea. Its sting is mild compared to that of the other species discussed here, but some unpleasantness and discomfort is to be expected. Victims can typically spray the affected area with vinegar and apply hot or cold treatments that will reduce pain and swelling. However, due to its classification as a box jelly, Irukandji Syndrome could be triggered, so it is important to remain vigilant if you are stung.