Lion’s Mane Jellyfish

Lion's Mane Jellyfish

  • Scientific name: Cyanea capillata
  • Size: Usually up to 70cm across but can grow to over 2 metres across and have tentacles more than 30 metres long.
  • Distribution: Generally found in cold and temperate waters. Found in northern European waters but absent from the Mediterranean and any further south.

The lion’s mane jellyfish is a rare sight in the United Kingdom and Ireland. It is most common around the UK is in the English Channel and off the coast of Cornwall, although it has been observed at many other locations including the Shetland Islands, north east coast of England and off the coastline of Wales.

This species is usually around 50cm across when found in British waters, but, as the largest jellyfish species in the world it can grow to two metres (6ft) across, and have tentacles close to 40 metres (130ft) in length, making it one of the longest animals in the world. It is usually an orange, red or yellow in colour, with a shallow umbrella. It has a number of thick tentacles as well as very long, thin tentacles which trail behind it as it moves through the water. These tentacles are used to catch all manner of sea creatures which the lion’s mane jellyfish comes across, with small prawns and shrimps, smaller jellyfish and pelagic crustaceans making up the majority of its diet, although small fish are also taken. Lion’s mane jellyfish may themselves become prey for sunfish and sea turtles. This species has a lifespan of around one year.

Lion's Mane Smithsonian
A life-size model of a lion’s mane jellyfish (alongside a thresher shark) at the Smithsonian Museum of Natural History in Washington D.C., USA.

The lion’s mane jellyfish has a very powerful sting which can cause serious harm to any humans which causes blistered red skin and intense pain. Most healthy people will simply have to wait for the pain to pass. However, in rare cases further complications such as muscle contractions and cramps, respiratory problems and even heart attacks can be caused by the lion’s mane jellyfish’s sting. Anyone finding a lion’s mane jellyfish washed up on the beach should also be aware that the tentacles of this species retain their potent sting long after the jellyfish has died, and dead specimens should therefore never be touched under any circumstances. Certain wind and tide conditions can see groups of lion’s main jellyfish cluster together in British waters, as seen off the coast of Cornwall in 2010.