4 of the most dangerous jellyfish known to man

A stunned beachgoer in Britain recently spotted an enormous 1m-wide barrel jellyfish washed up on a beach in Portland, Dorset. It is thought to be one of the biggest of its kind to ever appear on British shores, said media reports on May 8.

Warmer-than-average weather which is expected in Britain in the next few weeks could bring more of the super-sized sea creatures, said experts.

Although that particular species is harmless, there are some you might want to avoid if you chance upon them. Here are four of the most dangerous jellyfish known to man:

Sea nettles


Sea nettles can be found along the coasts of North America. They aggregate to form large "blooms" in the summer, posing a threat to swimmers.

Sea nettles can measure 30cm across, but it is their 2m-long tentacles that should be avoided. The sting from a sea nettle can leave a painful rash on the skin for around an hour, but it is not generally deadly.

Lion's mane jellyfish


The lion’s mane jellyfish is the largest jellyfish known to man. With a body or "bell" spanning 2.5m or more across and tentacles trailing over 30m, these monsters can weigh around a quarter of a tonne.

The lion's mane is a coldwater species and can be found throughout the North Atlantic, including Britain and cooler waters around Australia.

Its sting can be highly painful and potentially fatal. Like most jellyfish, its stings remain active for a long time after death. In a 2010 incident at a beach in New Hampshire, US, a single washed up lion’s mane jellyfish broke up and the fragmented tentacles stung a reported 150 people.

Irukandji jellyfish


The irukandji jellyfish is believed to be one of the world’s most venomous creatures, with a venom 100 times more lethal than a cobra’s.

As tiny as a matchstick, the irukandji is a silent, nearly invisible, killer found in the seas off northern Australia. This deadly species of jellyfish came to prominence in early 2002, when a 58-year-old British tourist, Mr Richard Jordon, was stung while swimming near Hamilton Island, off the coast of Queensland. He died several days later.

Experts say, however, that the much larger box jellyfish (below) still poses a bigger threat than the irukandji because it can kill an adult human much faster, usually within minutes.

Box jellyfish


Another extremely venomous jellyfish is the box jellyfish. Its body is about 20cm long while its tentacles can grow up to 4m. It is commonly found around Australian waters.

Like all jellyfish, its venom is found mostly in nematocysts in the tentacles. Nematocysts are tiny sacs containing tightly coiled, spring-loaded stings that inject the venom. Jellyfish use them to sting small fish before hooking the animal for feeding.

Symptoms of being stung include pain and raised red swellings that look like whip marks. Box jellyfish venom is deadly and can lead to death within minutes. Its neurotoxin may lead to breathing problems or cause the heart to stop suddenly.