Sexual cannibalism is a remarkably common mating habit among insects and arachnids — perhaps most famously, black widow spiders and preying mantises devour males after mating with them. There are a number of competing theories about why such a seemingly harmful trait would evolve. And now we've discovered one spider who evolved a way to escape sexual cannibalism, though not without sacrifice. The male Nephilengys malabarensis saves his head by detaching another part of his anatomy — the penis. Well, actually it's a palp, not a penis, but I digress.
The practice is called remote copulation (which for my money is the best neologism since teledildonics), 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.
Image: Nephilengys malabarensis female with a severed male palp (red box) lodged in her epigynum after copulation, and a half-cannibalized male at her side. Via the publication.