When I was a kid in San Diego, I often saw hoards of dead jellyfish on the beach. I was told that dead jellies can sting just like a live one. ([Eddie] Was you ever bit by a dead bee? [/Eddie]) So… Can they?
I’m guessing that nematocysts can remain “triggerable” after the jelly has died, until the cells themselves die. (How long would nematocyst cells “live” after the jelly itself has died?)
The jellies I saw as a kid were milky white with purple stripes. I’m pretty sure they were Purple Jellyfish (*Pelagia panopyra *).
Yes. I read that even after tendrils have dried, the can sting when they become wet again, although I can’t produce a cite offhand. But I read Discover and Sci Am regularly so it may have been in one of those.
Absolutely. I got stung (and came quite close to death) by the detached tendrils of a box jellyfish when I was ten. The docs said the stingers can remain active until the tentacle has entirely rotted away.
By what mechanism? If the cell is dead, how can it sting? I’m not talking about something analogous to stepping on a hypodermic needle that happens to be filled with some sort of acid. A person stepping on such a needle will feel the puncture of the needle and the residual acid may get into the bloodstream causing a “sting”. Imagine a severed arm with the needle-tipped syringe in its hand. Since the arm is dead, it can’t push the plunger of the syringe to inject the “venom”. If a nematocyst cell is dead, then how does it inject venom? Or is it like stepping on the needle?
I don’t know how it works mechanically, but both my mom and I can attest firsthand that dead jellyfish can sting like a $@(%@. I got stung right between the toes (I literally stepped on one, which was no fun, let me tell you!), and Mom swam into some detatched dead Portuguese man-o’-war tentacles and had what looked like whiplashes all over her back and arm for several days.
We discovered later that supposedly meat tenderizer will kill the pain from the venom. I never had the chance to try again, luckily.
Certainly it is true that pieces of box jellyfish tentacle will continue to sting after they are detached. Which presumably means that the jellyfish itself could be dead, burned and buried but if you touched a broken off piece of tentacle, you could still be stung.
I once saw Ben Cropp (gung ho Australian marine doco maker) put two tiny pieces of box jellyfish tentacle on his arm deliberately in order to test out whether methylated spirits or vinegar were better treatment (the latter, by the way). Believe me, the pain on his face left you in no doubt as to the effectiveness of a broken off piece of tentacle.
According to this page the mechanism by which the nematocysts are made to cease firing by the application of vinegar is not well understood, which I’m guessing means that the mechanism by which they fire might also not be well understood.
[Miracle Max] Mostly dead! There’s a big difference!
[/Miracle Max]
Good question, askeptic. If the nematocysts are still capable of stinging after the bell part of the jelly is dead, are they still alive? When do they become dead?
Princhester: Interesting article; but I have to admit that I didn’t read the whole thing. (A little dense for pre-coffee reading.)
As I understand it, the nemocyst itself is more like a mechanical device than a living thing. It’s basically a spring-loaded harpoon mechanically set to fire and inject venom if touched, and doesn’t need to be connected to a living cell to still be functional. It’ll remain able to fire so long as it’s still physically intact, even if the rest of the jellyfish is gone.
Jellies are really fascinating creatures. Their movement is intriguing – how do they move their bells? Invisible muscles? (Those were rhetorical questions. Just impressions that someone might have upon first seeing one.) And the bioluminescence! How cool is that?
The discharge apparently involves a change in the premeability of the capsule wall. Under the combined influence of mechanical and chemical stimuli, which are initially received and conducted by the cnidocyte ( note: cnidocytes are the general cell-type under which nematocysts are classified ) surface structure, the operculum or apical flaps of cnida open. Although cnidocytes usually fire as independant effectors, discharge can apparently be effected by nerve impulses from an associated neuron terminal, and neuronal connections may serve to bring about coordinated firing by a large number of nematocysts.
From Invertebrate Biology, fifth edition by Robert D. Barnes ( 1987, CBS College Publishing ). Note added for clarity.
So they fire mechanically, but while live at least some jellyfish can also coordinate their use. Always handy to hang on to old textbooks ;).
They say some people watch NASCAR for the crashes, but my AP Biology teacher would rather go to the beach and watch people walk on dead jellyfish and/or hydras(?). He says their tentacles are still active (to reiterate what is previously posted). He would just sit back and watch… Sick! Sick! Sick!
So, a word to the wise is sufficient, and if in doubt, don’t!
Your Cliche-a-Day,
I mean it is not like you can check its pulse. 
