Not all jellies sting, but the sea nettle does. It hunts tiny drifting animals by trailing those long tentacles and frilly mouth-arms, all covered with stinging cells. When the tentacles touch prey, the stinging cells paralyze it and stick tight. From there, the prey is moved to the mouth-arms and finally to the mouth, where it's digested.
There is mounting evidence that human influences in coastal habitats may be creating conditions more favorable to jellies, leading to an increased frequency of blooms and reduced populations of larval fishes. The high abundance of sea nettles makes scientists believe they play a significant role in the planktonic food chain. They may seem insignificant when washed up on a beach, but gelatinous animals are certainly worthy of our attention and study.
Some jellies commute 3,600 feet (1,097 m) up and down in the water daily—try that without a submarine!
Larval and juvenile cancer crabs may hitch rides on the sea nettle's mouth-arms, dropping off as the jelly comes inshore. These crabs may be feeding on the jelly, as many of the jellies with crabs have been observed to be quite tattered.