Do all jellies sting?

Yes, they do. All jellies have specialized structures called cnidoblasts. Inside the cnidoblasts are capsules called nematocysts. Inside each nematocyst is a coiled, hollow thread. Nematocysts are triggered by mechanical (touch) or chemical stimuli. When they fire, the thread turns inside out, pierces its prey and delivers its venom. A jelly’s tentacles and oral arms are covered with thousands of these spring-loaded little death traps.

But not all nematocysts are created equal. The sting of a sea wasp can be deadly inside of five minutes. The famous “stingless” jellies of Jellyfish Lake in Palau however, have a venom so weak; you’d have to give them a good lick to have any effect at all.

But we’ve only scratched the surface here. Check back often at for more insight about your favorite beach discoveries.

Jim Wharton
Vice President, Education Division, Director, Center for School and Public Programs, Mote Marine Laboratory

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