RETROACTIVE ARACHNOPHOBIA WARNING: spider pic.
Seen here in a red rectangle like it's cover of TIME magazine, a male Nephilengys malabarensis spider's penis is left in a female during mating with the hopes she won't cannibalize him after the 16-legged dance is over. Unfortunately for him, it didn't work this time (he's the little guy on the left being eaten).
The practice is called remote copulation...and while it may seem obviously a bad idea to chop off your breeding organs, it does have some advantages. For starters, the male spiders aren't necessarily killed during the act -- but far more importantly, they continue to transfer sperm after detachment. In fact, the emasculation increases the number of sperm transferred, especially when initiated by the female.
Some researchers have noted that the eunuch males are more aggressive and agile after they lose the organ, and that the detached palp may serve to block the female genitals in order to ensure the male's loss is his gain when it comes to paternity.
While some guys might argue being killed immediately after sex with an Amazon 20-times their own size isn't actually a bad way to go, those guys are undoubtedly virgins. "Live to masturbate another day" the saying goes.
Thanks to Luke and boobiedo, who are both convinced there's an untapped opportunity in the spider strap-on market.