The back rub is a strategic tool that allows you to initiate a sexual encounter with your partner without actually having to say the words "Hey, let's bone" (like dogs do, we assume). It's a win-win situation for everyone involved: The girl gets a scientifically proven relaxing treatment that can even cure some actual medical problems, while the dude greatly increases his chances of touching boobie later that night.
Thankfully the incidence rate of a female human devouring her lover is fairly low.
But it's only because we're so evolved and civilized that we've arrived at this ritual, right? Nope -- spiders do it, too. According to researchers, there are a few species of spider that have been observed massaging the backs of their partners before mating. Here's some footage of it, presumably taken from a hidden camera placed by the male spider himself.
C. Frank Stramer
If you feel this little guy crawling up your neck, don't worry, it just wants to fuck you.
One of the species that does this is the golden orb-weaver spider, where the male is so small compared to the female that he can actually climb all the way on top of her before putting silk on her back and spreading it around in massage motions. This might sound extremely romantic to you, but it has nothing to do with romance: It's all about survival.
Like we said, the female is way bigger than the male -- this means he has a lot to grab on to, but it also means that if she isn't in the mood for playing around or simply doesn't like the way he's doing it, she will eat him. Um, literally.
Dr. Raju Kasambe
We can't tell if he's being eaten or if she just pooped him. Either way, ouch.