25 Fun Facts About Jellyfish for Kids + Immortal Jellyfish Facts

Jellyfish might look like floating blobs, but they’re some of the most fascinating creatures in the ocean! With their wobbly bodies, stinging tentacles, and ancient history, jellyfish have plenty of secrets to share. Whether you’re a curious student or a teacher looking for a fun science topic, dive in to discover the wild world of jellyfish.

What are 10 fun facts about jellyfish?

• Jellyfish are ancient. They’ve been around for over 500 million years—older than dinosaurs!

• They’re mostly water. A jellyfish’s body is about 95–98% water, which is why they seem to disappear when they dry out.

• No brain, no bones, no heart. Jellyfish don’t have a brain, bones, or a heart. They use a simple nerve net to sense the world.

• They can glow in the dark. Some jellyfish are bioluminescent, meaning they can make their own light.

• Jellyfish come in all sizes. Some are as small as a pinhead, while the Lion’s Mane jellyfish can have tentacles over 100 feet long!

• They have stinging tentacles. Jellyfish use special cells called nematocysts to sting and catch their food.

• Jellyfish can be found everywhere. They live in every ocean, from the surface to the deep sea.

• Some jellyfish are “immortal.” The Turritopsis dohrnii jellyfish can revert to its baby stage and start life over again.

• They have a unique way of moving. Jellyfish “swim” by pulsing their bell-shaped bodies, pushing water behind them.

• A group of jellyfish is called a “smack.” That’s right—if you see a bunch of jellyfish together, you’ve found a smack!

How old are jellyfish?

Jellyfish are some of the oldest animals on Earth. Fossils show they’ve been floating in the oceans for more than 500 million years—long before dinosaurs, trees, or even sharks!

Do jellyfish have brains?

No, jellyfish don’t have brains. Instead, they have a simple network of nerves called a “nerve net” that helps them sense light, touch, and movement.

“A jellyfish doesn’t think about what’s for lunch—it just drifts along and lets its tentacles do the work!”

What do jellyfish eat?

Jellyfish are carnivores. They eat tiny fish, plankton, and even other jellyfish! Their tentacles sting and paralyze their prey before moving it to their mouth.

Where do jellyfish live?

Jellyfish live in every ocean on Earth. You can find them in warm tropical seas, icy polar waters, and even in some freshwater lakes.

Are jellyfish dangerous?

Most jellyfish stings are harmless to humans, but some species—like the box jellyfish—can be very dangerous. It’s always best to look, not touch!

What is the largest jellyfish?

The Lion’s Mane jellyfish is the largest known species. Its tentacles can stretch over 100 feet—longer than a blue whale!

How do jellyfish sting?

Jellyfish have special cells called nematocysts on their tentacles. When something brushes against them, these cells fire tiny harpoons that inject venom.

“If you see a jellyfish at the beach, admire it from a distance—its tentacles might be ready to sting, even if it looks harmless!”

How long do jellyfish live?

Most jellyfish only live for a few months, but some can survive for several years. The “immortal” jellyfish can potentially live much longer by restarting its life cycle.

What is a group of jellyfish called?

A group of jellyfish is called a “smack.” Sometimes, you might also hear them called a “bloom” or a “swarm.”

Spotlight: Immortal Jellyfish Facts (Turritopsis dohrnii)

• Immortal Jellyfish Overview: Known as the “immortal jellyfish,” this species has the rare ability to revert its adult body back into a polyp (baby stage) when injured or stressed. That means it can, in theory, start its life cycle all over again—potentially avoiding natural death.

• Immortal Jellyfish Size: They are very small, usually less than 4–5 millimeters across (about the size of a pinky fingernail).

• Immortal Jellyfish Age/Lifespan: While most jellyfish live for only a few months to a few years, the immortal jellyfish can potentially live indefinitely by resetting its life cycle.

• Immortal Jellyfish Sting: Their sting is mild and harmless to humans.

• Immortal Jellyfish Habitat: Found in temperate and tropical oceans around the world, often in the Mediterranean Sea and waters off Japan.

Jellyfish may look simple, but they’re full of surprises! Next time you spot one, you’ll know just how amazing these wobbly wonders really are.