The lion's mane jellyfish (Cyanea capillata) is the world's largest jellyfish
- their bells can be over 8 feet across. They have a mass of thin tentacles that resemble a lion's mane, which is where their name originates. Reports of tentacle size in lion's mane jellyfish vary from 30 feet to 120 feet - either way, their tentacles extend a long way, and one should give them a very wide berth. This jellyfish also has lots of tentacles - it has 8 groups of them, with 70-150 tentacles in each group.
The color of the lion's mane jellyfish changes as it grows. Small jellyfish under 5 inches in bell size are pink and yellow. Between 5-18 inches in size, the jellyfish is reddish to yellowish-brown, and as they grow past 18 inches, they become a darker reddish brown. Like other jellyfish, they have a short lifespan, so all these color changes may happen in a period of about one year.
Encountering a lion's mane jellyfish probably won't be lethal, but it won't be fun, either. A lion's mane jellyfish sting usually results in pain and redness in the area of the sting. The sticky tentacles of a lion's mane jellyfish can sting even when the jellyfish is dead, so give lion's mane jellyfish on the beach a wide berth. In 2010, a lion's mane jellyfish washed ashore in Rye, NH, where it stung 50-100 unsuspecting bathers.