Do jellyfish have the deadliest venom in the world?

You may have been stung by a jellyfish on a trip to the beach or a dip in the ocean. But, while most jellyfish stings do little more than annoy you, the sting of the box jellyfish can literally scar you for life -- if it doesn't kill you first.

The venom of this pale blue, almost transparent, invertebrate is among the most deadly in the world, capable of killing a human in under five minutes [source: Thompson]. This animal has enough venom to take out 60 adults [source: Bartalucci]. Also called sea wasp and marine stinger, the box jellyfish injects its venom by way of the many tentacles dangling from its bell, or body. (The box jelly gets its name from the boxy shape of its bell.) Each tentacle contains about 5,000 stinging nematocysts, housed in cells called cnidoblasts. Nematocysts are like little stinging darts that fire whenever the tentacle comes in contact with chemicals on the surface of its prey. (You can learn more about various species of jellyfish by reading How Jellyfish Work.)

With up to 15 tentacles growing from each corner of the jelly's bell, and each one reaching a possible 10 feet (3 meters), that's a lot of miniharpoons ready to deliver venom into a victim's body. A single encounter can leave you with thousands of stings, and the powerful venom doesn't waste any time getting to work. Many victims stung at sea go into shock or die of heart failure before they can even reach the shore [source: ­National Geographic].

Not only is the box jellyfish venom damaging to the heart and nervous system, it's also dermonecrotic, meaning it's capable of killing skin cells and underlying tissue, leaving you with dead, blackened skin and potentially permanent scarring. To make matters worse, your initial instinct to shake the offending stingers off makes the tentacles contract and stick tighter to your skin, possibly releasing even more stingers into your already burning flesh.

Thankfully, there's somewhat of a cure if you can get to it fast enough. Acetic acid solutions like have been shown to render the stinging cells harmless, preventing them from firing more toxins into your body. (Antivenin is also available.) Or you could just do what some savvy Aussies do and wear women's pantyhose when you head out to the beach. Apparently nylon prevents the jellies from stinging since they can't detect the chemicals on your skin.

Australians have quite a bit of experience dealing with deadly creatures. Many of the world's most venomous offenders live Down Under. Along with the box jelly, which lives mainly off the coast of Northern Australia and throughout the Indo-Pacific region, the island continent lays claim to several other specimens vying for the grand prize of most venomous animal. Find out which one claims that top spot on the next page.

Actually, the grand prize winner of most venomous animal may never be found. Due to the somewhat flimsy nature of testing venom's potency, there's some disagreement about which animal comes out on top.

A common method of measuring the toxicity of a substance is LD50, expressed as the dose that kills half of the test animals the substance is used on. LD50 usually is represented by the amount of venom (or other chemical) given for every 100 grams or 1 kilogram of the test animal's body weight [source: Canadian Centre for Occupational Health and Safety]. The "LD" stands for "lethal dose," and "50" represents 50 percent of test subjects -- the lower the value, the more potent the chemical. The LD50 of a box jellyfish is 0.04, while the LD50 of a coral snake is 1.3 [source: Lee, Fry]. Researchers are starting to phase out LD50 in favor of alternative methods that reduce the deaths of test animals.

While this standardized measure is a good baseline for comparing the relative strength of different venoms, a number of things can alter the value. For one thing, the test animals -- usually rats or mice but sometimes rabbits, hamsters and guinea pigs -- don't necessarily have the same response to the venom that other animals, like humans, would. Even when the test animal's weight is taken into consideration, one species can have a totally different reaction from another. Other things that can affect the LD50 value include the way the chemical is administered and the age, size and geographic origin of the animal that provided the test venom [source: Kimball, Venom Supplies].

­­That being said, there are definitely several venomous villains that stand out above the crowd. High on the list is another marine animal and Australian native, the geographic cone snail. Found along the coral reefs of the Indo-Pacific, these intricately patterned, brown-and-white shelled gastropods have especially potent venom that paralyzes their prey almost instantly. When a tasty fish or snail wanders by, these attractive, harmless-looking shells extend a tubelike organ outfitted with what resembles a minispear. This weapon injects prey with a venom so powerful that victims may die before they even realize that they've been bitten [source: PBS].

Another deadly Australian animal is the inland taipan, which produces the most toxic venom of any snake in the world. A venomous bite from this predator is powerful enough to kill 15,000 mice [source: California Academy of Sciences]. Before the antivenin was created, few people lived to tell about their encounter with this reptile.

The world's deadliest spider, the Sydney funnel-web spider, also lives in Australia. Its venom acts on the body's nervous system and can kill in under 15 minutes [source: California Academy of Sciences]. Named for their uniquely shaped webs, these notoriously aggressive spiders may cause you to develop a severe case of arachnophobia.