Well, this is romantic. It has been discovered by researchers at the National University of Singapore that males of a certain breed of spider — specifically, the tropical orb-spider Nephilengys malabarensis — will often castrate themselves either fully or partially, leaving a piece of their reproductive anatomy inside of the female during copulation.
Sounds familiar. This is just your typical love-em-'n'-leave-em, "I had sex with a spider and all I got was this stupid spider penis" situation, am I right, ladeeeeeeeeezzz? Thankfully, I am wrong (also, disgusting). Turns out that by detaching their genitals, male spiders become both more virile (with a 32-80% increase in endurance) and are able to reduce their weight by 4-9%. The weight loss allows for the male spider to become a better fighter in fending off other males from its female mate, thusly reducing sperm competition.
Just in case you mistake eunuchs as the biggest BAMFs of the spider world, think again. 75% of male Nephilengys malabarensis are eaten by their female paramours immediately following copulation. Take it away, Hall & Oates!
An Anomaly in Mating: Self-Castration Raises Reproductive Success [NYT]
Image via Qi Qi Lee