Are lions mane jellyfish dangerous

Answer 1

No. In spite of the fictional Sherlock Holmes short story, The Adventures of the Lion's Mane, they are not known to have caused a fatality. As a salmon fisherman in the Pacific Northwest, I have encountered Cyanea capillata most of my life. Their stings seldom penetrate most areas of skin, unless a tentacle encounters a cut or lesion. One exception is if you urinate when an unnoticed tentacle happens to adhere to your hands. Ouch. (And urine doesn't help, btw.)

My anecdotal story aside, it is probable that the larger (up to 8 foot in diameter) arctic variety can sting more viciously than the 2 foot variety that I have encountered. Studies show that vinegar can cause more stingers to fire in this species, so it would be wise to just pick any remaining pieces of tentacle off with your fingers (the pads of your fingers are too thick to be penetrated), and then soak in hot water, or apply ice packs. The effects of the sting are neither long lasting, unbearably painful, nor life-threatening.

Answer 2

Most encounters cause temporary pain and localized redness. In normal circumstances, and in healthy individuals, their stings are not known to be fatal.