Archive for September, 2013

Snail Power!

Posted: September 14, 2013 in Molluscs

Welcome to another episode of Horrific Animals of the World. This one contains, as usual, a romantic scene, a discussion on the uses of condoms in farming, venomous snails, tropical beaches and neurotoxins. Using all the above words in the same sentence has now probably got us onto all sorts of government watchlists.

So pretty standard, really.

Imagine that you are striding along with your significant other, on a warm, sunny evening, upon a sun kissed beach somewhere along the Indo-Pacific Ocean. The waves are lapping gently against the white sands; occasionally revealing submerged coral reefs. Palm trees wave slightly in the light, cooling breeze; and you and your loved one are at peace with yourselves, with each other, and with the world. Of course, the key word here is ‘imagine’, because in all likelihood you are reading this in Britain, which last had a warm, sunny evening in 1968.

The British version of the above scene. If you’re lucky.

You see a brightly coloured shell in the crystal clear waters, and, laughing, you bend down to pick it up, to present it to your beloved. It then immediately stings him or her, possibly lethally. This is – generally – considered a bit of a deal breaker when it comes to relationships.The problem was that you picked up a cone snail, Conus (also sometimes called Gastridium) geographus, and this snail is perhaps the most venomous snail in the entire world. (Is that even an award? Ed.)

Probably not worth breaking up with someone for. Or killing them.

Like all cone snails, C. geographus has the nifty little trick of stinging its prey with a harpoon loaded with toxins. This is done by a modified tooth, which when not in use is stored in an organ called the radular sac. Venom is then pushed into these modified teeth. When a prey animal (in the case of C. geographus, a small fish) is detected, a long tube called the probosis is extended towards the fish. The poison tooth is then ‘fired’ by muscular contractions, usually into the fishes gills, killing it pretty much instantly. C. geographus appears to use the ‘net hunting’ approach, in which small fish which wander into the snail’s mouth are eaten (Johnson and Stablum 1971, http://www.youtube.com/watch?v=qxw-8GYy_gY ). Other cone snails use a ‘hook and line’ method, shooting a harpoon towards a prey animal and then reeling it in.

Now, hopefully, your beloved is not a fish. Or even a mermaid. However, the problem is that these cone snails are extravagantly toxic; as in they can kill a person just as well as they can kill a fish. The common explanation for this is that because fish are fast moving, and snails are…well, not, a large dose of poison is needed to kill the fish instantly, before it escapes. However, Johnson and Stablum, who did the first studies of the feeding behaviour of this particular cone snail, speculate that the reason why these cone snails are so toxic is that it is actually for defence. Against what, they didn’t specify, so we are forced to assume that some awful hybrid of a shark and octopus lurks in the deeps, feeding exclusively on cone snails.

As studied in this highly respected scientific documentary.

Now, the good news is that a sting is not always fatal. That said, there are at least thirty cases (Nelson 2004) of deaths on record due to snail stings, which we can’t help but feel must be one of the most embarrassing, none-sexual things to have on your death certificate ever. There is no specific anti-venom, and treatment mainly appears to consist of just keeping you alive whilst your body breaks down the many, many, many, many, many toxins you have been injected with (http://animals.nationalgeographic.co.uk/animals/invertebrates/geographers-cone-snail).

Whilst most animals are content with having one or two major toxins in their bites or stings, the average cone snail has between 50 and 200 neurotoxins (Hu et al 2012); exactly which toxins are produced in what amounts appears to vary throughout the animal’s life. Together, these toxins block all sorts of vital receptors and channels vital for the continued function of your nervous system. Various experiments have shown that different toxins will make a mouse do anything from go straight to sleep, to shake, to run around in circles, to just shake its head. The sting also appears to contain a powerful painkiller, which at least means you may not be in screaming agony as your entire nervous system rapidly seizes up.

In fact, cone snails may be a boon for science in more ways than simply allowing scientists to take intriguing, snail based revenge. Since there are so many neurotoxins present, cone snail venom provides a rich source of potential new drugs and treatments (for example a painkiller more powerful than morphine, but without all the side effects of getting addicted); in addition to allowing scientists to be very, very specific in exactly which parts of the nervous system they can block. Indeed, some species of cone snails are now being farmed especially for their venom, with condoms being used as a vital part of this venom farming (Nelson 2004), despite the fact that asking for several dozen venomous snails, a fishtank and a pack of condoms will usually lead to a long series of hard, puzzled and unsympathetic stares.

Proof, yet again, that screaming β€œFOR SCIENCE!” excuses anything.

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