Beware the Hidden Dangers of Jellyfish… And What Happens if You Pick One Up

Many people enjoy spending their summers at the beach, listening to the waves, and exploring colorful tidepools. But too often, we forget that even the smallest and most unassuming creatures can be surprisingly dangerous, especially when we’re trespassing on their home turf. Jellyfish, often found washed ashore or trapped between rocks, are a good example. Even if they appear harmless, these special sea creatures will surprise you with how quickly they sting — even dead jellyfish!

Jellyfish Size

The world’s oceans are home to many kinds of jellyfish of various shapes, colors, and sizes. Some are surprisingly tiny — less than half an inch — while others grow to enormous sizes, with bells over 7 feet wide and tentacles stretching over 100 feet long.

The jellyfish featured in this video is likely a barrel jellyfish (Rhizostoma pulmo). While not the largest out there, barrel jellies are still quite big and can grow bells nearly 4 feet in diameter — the one in the video isn’t quite that big, but the man still has to use both hands to hold it. Barrel jellyfish have large, mushroom-shaped bells with frilly edges, eight large frilly arms, and small tentacles. Despite their large size, however, barrel jellyfish feed on tiny plankton using the tiny mouths on their tentacles.

How Jellyfish Defend Themselves

Jellyfish may be mostly water (about 95%), but they have a powerful defense. Their tentacles are covered in cnidocytes, tiny, specialized cells that house nematocysts. Nematocysts are venomous, harpoon-like stingers that can fire rapidly when triggered. When something brushes against a jellyfish’s tentacles, these nematocysts fire and inject venom, causing pain and irritation around the sting. Sometimes the venom can penetrate and spread through the bloodstream as well.

While some jellyfish are harmless to humans, others can be dangerous — or even deadly, like the Portuguese man-of-war and box jellyfish. Barrel jellyfish, like the one the man attempts to pick up in this video, aren’t deadly, but they can still sting. Their stings are usually mild; some people feel nothing, while others experience burning, itching, blisters, and rashes.

If You’re Stung by a Jellyfish…

A common myth often seen in movies and TV shows (like Friends) suggests that urine can relieve jellyfish stings. However, this is simply not true. In fact, urinating on a sting or even rinsing it with fresh water can actually worsen the pain by triggering the release of more venom, especially if tentacle fragments are still stuck in the skin.

Instead, the recommended approach is to first carefully remove any remaining tentacles — but be careful, as even detached tentacles can still sting! Then rinse the affected area with saltwater or vinegar and seek medical attention immediately.