Lion’s Mane Jellyfish – How Dangerous Are They?

By Archives •  Updated: 07/15/22 •  3 min read

The lion’s mane jellyfish (Cyanea capillata) is a species of jellyfish that is found in the North Atlantic, the North Pacific, and the Arctic Ocean. The jellyfish can grow up to a foot long and have long tentacles that are covered in stinging cells. It is also known as the giant jellyfish, the arctic red jellyfish, or the hair jelly,

“Jellyfish” is a common term for different species of what scientists call cnidarians (silent ‘c’ when pronounced).  The root of cnidaria in Greek means ‘nettle’. a reference to the stinging tentacles of some species. Cnidaria is a phylum of the animal kingdom found mostly in marine environments but also in fresh water.

The largest recorded lion’s mane jellyfish was measured off the coast of Massachusetts in 1865 and had a bell with a diameter of 7 feet and tentacles around 120 ft long.

Lion’s Mane Sting – Is It Dangerous

Cyanea capillata - Lion's Mane Jellyfish

Cyanea capillata Credit: Dan Hershman CC BY 2.0

For healthy people, the stings of this giant arctic jellyfish are not known to be fatal; vinegar can be used to deactivate the nematocysts, and meat tenderizer is said to be a good antidote to stings. If there is contact with a large number of tentacles, however, medical attention is recommended after exposure.

There could be a big difference between brushing a few tentacles with your fingertips at a beach and accidentally swimming into the jellyfish. The first sensation is more odd than painful and feels like swimming into warmer and sort of bubbly water.

Some minor pain will soon follow. Humans are usually safe from danger with the exception of people with certain allergies.

But in cases when someone has been stung over large parts of their body by not just the longest tentacles but the entire jellyfish (including the inner tentacles, of which there are around 1,200), medical attention is recommended as systemic effects can be present. Although rare, in deep water, severe stings can also cause panic followed by drowning.


Cyanea capillata are named for their ornate trailing tentacles that look like a lion’s mane. They can vary greatly in size, and can weigh up to 200 pounds.

Though capable of growing to a bell diameter of over 6 ft 7 in, those found in lower latitudes are much smaller than their far northern counterparts, with a bell about 20 inches in diameter. Juveniles are lighter orange or tan, very young lion’s manes are occasionally colorless and adults are red and darken as they age.

The bell, or upper body, of the Lion’s Mane is sectioned into eight lobes that resemble an eight-pointed star, each lobe contains about 70 to 150 tentacles, arranged in four fairly distinct rows. Along the bell rim is a balance organ at each of the eight indentations between the lobes – the rhopalium – which helps the giant arctic jellyfish orient itself. From the central mouth extend broad frilly oral arms with many stinging cells.

The long, thin tentacles which emerge from the bell’s subumbrella have been described as “extremely sticky”; they also feature the infamous stinging cells. The tentacles of larger specimens may trail as long as 100 ft or more, earning this creature the status of one of the longest known animals in the world.


  1. Jeanna Bryner, How One Jellyfish Stung 100 People, Live Science, July 22, 2010
  2. Carwardine, M. 1995. The Guinness Book of Animal Records. Guinness Publishing. p. 232.
  3. Kozloff, Eugene (2003). Seashore Life of the Northern Pacific Coast. University of Washington Press. pp. 54, 56 (1983 edition)
  4. Mahon, Andrew; Mallinson, Tom E (2020). Lion’s mane jellyfish sting. International Paramedic Practice. 10 (2): 46–48.

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