Why Jellyfish Float Like a Butterfly—And Sting Like a Bee

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Jellyfish don’t have a heart, or blood, or even a brain. They’ve survived five mass extinctions. And you can find them in every ocean, from pole to pole. What’s their secret? Keeping it simple, but with a few dangerous tricks.

DEEP LOOK: a new ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe and meet extraordinary new friends. Explore big scientific mysteries by going incredibly small.

--- Why do Jellyfish Sting?

Jellyfish sting to paralyze their prey. They use special cells called nematocysts. Jellyfish don’t have a brain or a central nervous system to control these stinging cells, so each one has it’s own trip wire, called a cnidocil.

When triggered, the nematocyst cells act like a combination of fishing hook and hypodermic needle. They fire a barb into the flesh of the jellyfish’s prey at 10,000 times the force of gravity – making it one of the fastest mechanisms in the animal kingdom. As the barb latches on, a thread-like filament bathed in toxin erupts from the barb and delivers the poison.

The nematocyst only works if the barb can penetrate the skin, which is why some jellies are more dangerous to humans than others. The smooth-looking tentacles of a sea anemone (a close relative of jellies that also has nematocyst cells) feel like sandpaper to the touch. Their nematocysts are firing, but the barbs aren’t powerful enough to puncture your skin.

--- Read the article for this video on KQED Science:


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