Jellyfish swim by expanding the body like an opening umbrella, then pulling it together again rapidly. This squeezes water out from beneath the body and the jellyfish moves upward. When these movements stop, the jellyfish sinks to the ocean floor. On its way down, it catches small animals that touch its tentacles or oral arms. The victim is then passed to the mouth of the jellyfish and swallowed.
Some jellyfish can inflict painful and even dangerous stings to people.
Jellyfish called sea wasps inject their victims with a poison that is deadlier than any snake venom. Some people have died less than three minutes after being stung by a sea wasp. Sea wasps are found near the coasts of northern Australia and the Philippines. Scyphozoan jellyfish produce their young from eggs. Each egg develops into a tiny polyp, a stage in which the animal looks like a hollow cylinder.