The primary threat does not come from their large primary spines, but from their smaller, secondary spines. These spines are barbed and carry venom. The spines are brittle, and after pucturing the skin they often break within the wound. They have tentacles that hang down from there body, trailing in the water. These tentacles used to sting small fish and carry them to the central mouth.
Some jellyfish can kill humans with their sting.
They have about half a million stingers. When its tentacles touch a fish such as a herring, a tiny, barbed thread lashes out and releases venom. They have enough posion to kill a fish or kill human life.