Jellyfish (often called jellies) have lived on Earth for millions of years. They are found in every part of the ocean.
There are thousands of different types. Jellies can be smaller than a grain of sand or bigger than a car.
Don’t let their name fool you. Jellyfish aren’t actually fish. They’re invertebrates (in-VEHR-tuh-brayts). That means they don’t have any bones. They don’t have any brains or teeth either.
Right now, jellies are taking over oceans around the world. It’s a population explosion that has some people wondering: Why are there so many jellyfish?
Scientists think there are a few reasons. One is overfishing. People catch huge numbers of the fish that eat jellyfish. This helps the jellyfish population grow.
Also, chemicals can end up in the ocean. These chemicals kill off many sea creatures. But they don’t kill jellyfish.
Even global warming may be good for jellyfish. The ocean is getting warmer. But jellies don’t seem to mind. Some even have more babies in warmer water!
Why do people care? Because these bags of goo can cause a lot of problems.They can clog the pipes of power stations. This can cause homes and buildings to lose electricity.
Also, jellies have tentacles with stingers on them. Their stings can kill fish—and hurt people.