You have to hand it to spiders, they're so crafty, building their fancy webs and always managing to crawl out of your shoe and spook you just when you're least expecting it. But there is one kind of spider that has really gone above and beyond the call of duty: The orb-web spider, ephilengys malabarensis, has a detachable penis—actually it has two of them.
The spiders have a pair of organs that transfer sperm, which are called palps and are basically like tiny penises. While the male spider is making sweet love to a lady, he can just get up and walk away in the middle of the act, leaving one of his palps, which keeps pumping, behind. Neat trick.
Except this isn't just for the sake of convenience. The spiders are sexually cannibalistic, so the ability to walk away mid-coitus is actually a real life saver. The palps detach from their bodies either because they scurry away in hopes of not being eaten or because the lady spider pushes them off (and then possibly eats them).
There are also some serious drawbacks to this set-up. Having only two palps means each spider has just two chances to mate in their entire lives—if they're lucky. Not very good odds. Furthermore, Daiquin Li, from the University of Singapore, says the detachable organs can easily be damaged, though he specifies, "it's usually just the tip." Oh, spiders, why are you so fragile? But, you know, maybe it's better if they don't end up being able to mate in the end. Then they can just enjoy life without worrying that some woman is going to bite their head off for walking away during the middle of sex.
Spider's Detachable Penis Finishes Without Him [LiveScience]
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