You Didn’t Touch These Jellyfish, but They Can Sting You With Tiny Grenades

You Didn’t Touch These Jellyfish, but They Can Sting You With Tiny Grenades

Jellyfish are very sneaky about stinging. Most are silent. Some have venom that kicks in on a time delay. Many species even manage to get in a few zingers after they’re dead.

But according to research published Thursday in Communications Biology, the stealthiest stinging strategy belongs to Cassiopea xamachana, a species of upside-down jellyfish found in the Caribbean Sea, the Gulf of Mexico, and warm parts of the Western Atlantic like the Florida Keys. When disturbed, this creature acts like a space-movie mother ship — it emits tiny balls of stinging cells that then swim around on their own, zapping anything in their path.

These “self-propelling microscopic grenades,” which the researchers have named cassiosomes, also appear to stun and kill prey for the jellyfish, said Cheryl Ames, an associate professor at Tohoku University in Japan and lead author of the study.

The finding is “paradigm-shifting” and will change how researchers think about how jellyfish eat and sting, said Angel Yanagihara, a jellyfish envenomation expert at the University of Hawaii who was not involved with the study.

But looks can be deceiving. Dr. Ames, who usually studies deadly box jellyfish, always covers up completely for dives. Even so, she noticed that when she and her colleagues admired the upside-down jellies, they often came out of the water covered in “itchy and irritating” stings, she said.

Others were experiencing the same phenomenon even when they were “just handling the water” of an aquarium that these jellyfish had been in, she said. One aquarist told her he had repeatedly replaced the heater in an upside-down jellyfish tank, assuming a faulty wire was shocking him.

The U.S. Navy has long been curious about difficult-to-source jellyfish stings, said Gary Vora, the deputy laboratory head within the Center for Bio/Molecular Science and Engineering at the Naval Research Laboratory in Washington, D.C., and another author of the paper. Navy divers will sometimes get in what looks like clear water, and end up “lit up like a Christmas tree,” he said. “You have evidence of a sting, but you never saw what stung you.”

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