Most venomous jellyfish

The most venomous jellyfish is box jellyfish (Chironex fleckeri) found off the coast of northern Australia. On average it is responsible for one death a year. As little as 2 m (6 ft 6 in) of total tentacle contact is enough to be lethal. Each jellyfish has 60 tentacles, which may be up to 4 m (13 ft 1 in) long, and therefore theoretically a large jellyfish has enough venom to kill up to 120 people.

Death may result from one of two ways. First is that the pain is so intense that the person is overwhelmed and dies from shock. If they survive that, the venom can directly cause lethal cardiovascular collapse.

At least 70 people have died just in Australia over the past century, with some victims dying within four minutes if medical aid is not available. First aid consists of using vinegar to wash off any tentacles stuck to the body. While this has no effect on the venom already injected, it neutralizes the stinging cells and therefore prevents further venom from being injected. There is an antivenom made in Australia for neutralizing the injected venom.