I’ve never wanted to go to Australia. It sounds like a fun place, with beaches and warm weather and Vegemite, but I will never go there. There’s a very simple and very toxic reason: pretty much every extremely venomous animal lives in Australia. Just think about it. Most venomous snake: inland Taipan, lives in Australia. Most venomous spider: contentious (usually cited as the Brazilian wandering spider), but the funnel web spider, which lives in, you guessed it, Australia, is right up there. Most venomous fish: the stonefish, which lives in the waters around Australia and whose antivenin is the second most used in Australia. Most venomous octopus: blue ringed octopus. One of the only living venomous mammals, the duck-billed platypus, lives in Australia. And the most venomous jellyfish: the box jellyfish, which are mostly found in waters around Australia.

After reading all this, if you still want to go to Australia, you’re crazy. I’d much rather vacation in New Zealand where venomous animals just don’t exist. Anyway, I’ve talked about one of these animals in this blog already (the Inland Taipan), and today want to investigate the box jellyfish. Not only is it the most venomous jellyfish, it is one of if not the most venomous animals in the world.

The box jellyfish has a bell that can reach 35cm (about the size of a basketball), and tentacles that reach three meters in length. The numerous tentacles are attached at the corners of the bell, giving the jellyfish its namesake shape. Millions of tiny hooks line each tentacle, and these are part of what makes the jellyfish so deadly. Each of the hooks (nematocysts) contain venom, and they are the mechanisms the jellyfish use to deliver it. So when you come into contact with a box jellyfish’s tentacles, millions of hooks are injecting you with a highly potent venom. Not much fun.

The venom of the box jellyfish causes intense pain, and can kill adult humans. The toxins in the venom make cells porous, which allows potassium to leak from them, causing cardiovascular failure and death within two to five minutes. Apparently rubbing the affected area prevents any unused nematocysts from firing, so this should be done immediately in case of a sting. An antivenin is available for box jellyfish stings, but often it is not administered quickly enough to prevent death in serious cases. So don’t get stung by one! And watch out for dried tentacles, as wetting or touching them can reactivate the nematocysts, and sting you.

A box jellyfish with many very very dangerous tentacles.
A box jellyfish with many very very dangerous tentacles.

Unlike most jellyfish, box jellyfish can swim. Most jellyfish only float float with the current going wherever it takes them. Box jellies, however, can move up to four knots, and swim up freshwater rivers to mate. Once they reach these rivers, males and females release their respective gametes into the water and then die. I guess mating isn’t that much fun for box jellyfish.

Baby jellyfish known as polyps swim around until they find a suitable place to attach themselves, where they stay until they change into a medusa (the form of an adult jellyfish). While in the polyp stage, the jellyfish relies on plankton for food, and can reproduce asexually. Once developed into a medusa, jellyfish eat small fish and prawns. They use their tentacles to capture and kill their prey. One interesting thing about box jellyfish is their 24 eyes, which can detect light and dark but probably not shapes. The jellies also can detect vibrations, which are thought to aid in prey capture.

Box jellyfish may be the most venomous animals on the planet; its main competitors are those mostly species in and around Australia. Why anyone lives there, I’ll never know. If you do visit, stay away from everything! It’s all venomous, I swear.