The spider that loses its penis during sex to make it more fierce in battle against love rivals

The phrase ‘eunuch’ has derogatory  connotations for us humans – but it is a different matter for  spiders.

The male nephilengys malabarensis spider  loses its spider penis when it has sex with a female, which is in itself a  clever (if potentially painful) evolutionary trick, as it plugs up the lady  spider’s genitals and stops other men impregnating it.

But that is not the only clever purpose – the  male spider then has to defend his female against other spiders hoping to have a  try – and without the extra weight of the sexual organs, it can fight as a much  stronger warrior.

The researcher team said: ‘Prior work has  demonstrated that eunuch spiders are superior fighters, we here pinpoint a  mechanism that enables eunuch’s greater endurance.

‘Our present results imply that palp weight  poses significant physical costs to males.’

Up to 75 per cent of the spiders do not even  get to this stage, indeed 75 per cent of them get eaten by their  partner.

But if they do survive, and find themselves  without one or both of their palps – their equivalent of a penis – they will  protect their would-be eater, and have an advantage without the burden of their  privates.

According to MSNBC, the researchers tested this by amputating either one  or both palps from spiders, and exhausting them by prodding them until they  stopped moving.

They found that removing one palp reduced the  spider’s body weight by four per cent, and removing both reduced it to nine per  cent. But their endurance increased by 32 per cent and 80 per cent  respectively.

The scientists speculate that the spiders  fight more without their palps because they have ‘nothing to live for’ other  than protecting potential offspring – and without the drag of their privates,  they could fight for longer.

The study will be published in this month’s  Biology Letters.

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