Lion's mane jellyfish

The lion's mane is the giant of cold northern seas, with a reddish or yellowish-brown bell and eight clusters of tentacles, each cluster holding 70 to 150 or more. It is usually 30 to 50 cm across in British waters, but the largest have been reported at around 2 m, which makes it a contender for the world's largest jellyfish. Accounts of its sting range from moderately painful to very severe, with blisters and muscle cramps. Its biggest risk on a beach is that it keeps stinging long after it strands, and tentacles that break off in the water can still sting swimmers who never saw the bell. Larger animals are most common from June to September.