Jellyfish Facts

Jellyfish are saltwater creatures. With more than 1,500 varieties, the jellyfish can be found worldwide, including many coastal areas of the United States. Jellyfish varieties include types that sting and types that do not sting. Stinging jellyfish fall into the category known as medusae. Non-stinging jellyfish are ctenophores or comb jellies. The jellyfish is comprised of 95 percent water.

Life cycle

Jellyfish produce sexually. According to the Auburn University Marine Extension and Research Center, "the fertilized eggs develop into free-swimming larvae. The larvae settle to the bottom and form polyps." These polyps eat tiny marine organisms and "eventually develop into strobilating polyps when the polyp body divides into segments." The segments finally separate and become an ephyra, which is the final stage a jellyfish must travel through before becoming an adult. The adult jellyfish stage is called the medusa stage. Jellyfish live for an average of about one year.

Jellyfish stings

Within the tentacles of an adult jellyfish are nematocysts. The jellyfish uses these cells to catch food by stinging the prey with a protein toxin from the nematocyst. A small fish stung by a jellyfish becomes paralyzed and the jellyfish can capture it easily and eat it as a meal. When humans are stung, the affected area can be painful, swell and turn red. Some people can have allergic reactions to jellyfish; these reactions can be life threatening and need immediate medical treatment.


A bloom is the term used by scientists when any species of plants or animals suddenly appear, states the Monterey Bay Aquarium. The Smithsonian cautions that the terms swarm and bloom should not be used interchangeably when discussing jellyfish. "A swarm refers to jellies that collect in one area as a result of strong winds or currents, whereas a bloom is a dense cloud of jellies caused by an actual spike in reproduction."

Jellyfish blooms have clogged the water inlets at power plants in Scotland, Japan, Israel and Florida, reports the BBC. Jellyfish blooms also negatively impact fishing industries by clogging nets and more. This type of jellyfish infestation has been responsible for heavy monetary losses for some of the fishing industries in Japan, the BBC states.

Jellyfish diversity

The box jellyfish has one of the most venomous stings of all jellyfish. Also called marine stingers or sea wasps, the box jellyfish contains a toxin that can attack a human's heart and nervous system. A sting from a box jellyfish needs immediate medical attention. The box jellyfish can be found in the waters off the Northern Australian coast. The Lion's Mane jellyfish is very different than the jellyfish you may see at city aquariums. It is the largest type of jellyfish and can measure more than six feet in diameter with tentacles that can be almost fifty feet long, states National Geographic.

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