One of the things that I find interesting is how potent the tools some predators use to hunt can be. Call me anthropocentric but those that are lethal even to humans are especially interesting to me. As a result, I’ve decided to blog about one deadly critter every fortnight. This fortnight’s selection is Chironex fleckeri, a box jellyfish that is found in the waters off Australia.
This jellyfish apparently has tentacles up to 3 meters in length (when hunting) trailing behind its cuboidal head (hence the name ‘box jellyfish’ and classification under the Class Cubozoa. These tentacles are laden with nematocysts, or stinging cells, which deliver venom when triggered.
Nematocysts themselves are pretty interesting in how they operate, they have a tube with barbed tips which delivers venom from a venom sac, a trigger hair or a cnidocil and a nucleus, all packed into a capsule with a lid, which is called an operculum.
When the cnidocil brushes against prey, it triggers the opening of the operculum, the venom tube springs out like a whiplash, the barbs penetrate the skin of the prey and the tube delivers venom. That is pretty much the modus operandi of nematocysts
If you’re wondering how single cells like that could penetrate human skin and deliver venom, the answer lies in the sheer speed of it all, for a nematocyst to achieve envenomation takes just 700 nanoseconds, (1 nanosecond = 10 to the power of -9 seconds) and achieves an acceleration of 5,410,000 g, which is 5 million times the acceleration due to gravity, and that is bloody quick.
I suggest you read the paper to find out how this was studied, the link is in the image caption (note – you can also bring up a full-resolution version of the image by right-clicking and selecting ‘view image’)
Now the reason Chironex fleckeri is deadly is not just due to having lots and lots of nematocysts, it has to do with the potency of its venom. The venom has multiple effects – it causes necrosis of the skin, which leads to an intense burning sensation, it is also cardiotoxic, where it paralyses the heart leading to cardiac arrest. While a significant amount of venom is needed for a sting to be lethal, a fatal dose, if delivered, can kill within 4 minutes. It is also neurotoxic and may lead to paralysis of non-cardiac muscles.
You may find relevant information on how Chironex fleckeri venom acts and what measures are used to deal with cases of envenomation from this paper
 A paper on the nature of the compounds found in C.fleckeri venom
 There is some evidence for these jellyfish being able to react to different colours differently (they have eye clusters) , that phenomenon is recorded and described in this paper
That is all from me regarding this fortnight’s choice of deadly critters. Next fortnight I will be picking something else.