Why do spiders have such potent venom?

11 April 2010

Question

Hi team,

Why have certain spiders evolved poison so powerful, one bite can kill a large mammal like a cow? Most spiders feed on other insects and so it seems venom many times weaker would have the same rapid and deadly effect. But there must be a perfectly good reason as nothing of this nature evolves by accident. Can you help?

Regards,

Ian Farr

Answer

Chris - It's not just spiders. There are many examples of organisms in the natural world that make toxins that are really, really toxic. As one researcher put it to me, it is a case of overkill, and they do it incredibly well. And the reason is because these animals have evolved to use and exploit a whole range of different prey rather than just one. And this means that because the prey animals are different, they therefore need to make a range of different venoms, which have action against the range of different prey. If they just use one, it would be very easy for one prey to evolve away from being sensitive to that particular venom. By using a range of different venoms and therefore targeting a range of different prey, there's no chance that it will start working. And over time, they've just continually updated and adjusted their repertoires so they have this amazing example of all these different molecules, some of which will work really well against one species, others less so. And when they sting us, some of them absolutely take us to the cleaners. And it's not just spiders, there are many, many examples that is going all around nature.

Dave - Well, I guess also, some prey will evolve to be more resistant to them so that doesn't work as well. So they have to get stronger and stronger.

Chris - Yes. But also, it means that some of these genes do, at the same time, become redundant, some of these venoms. And so they actually lose the ability to use them and therefore those genes stop working. They're still hiding in the genome, but they just don't turn those genes into products anymore. But yes, they're very interesting.

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