A group of jellyfish is called a smack. When huge numbers of jellyfish, or any plant or animal, appear suddenly, it is called a ?bloom.?
Jellyfish in a bloom can number in the millions. Because jellyfish are plankton and are not strong swimmers, they are at the mercy of the ocean currents. A bloom often appears when two ocean currents meet. A strong breeze can blow the bloom to shore, stranding the jellyfish.
There are many jellyfish types, and not all of them sting. The stinging variety are called ?medusae,? while nonstinging jellyfish are ?comb jellies? or ?ctenophores.? The typical jellyfish lives for less than a year, but some live for only a few days.