If Fifty Shades of Grey has taught us anything about the human condition, it's that people all over the world get turned on by the idea of getting tied up in the bedroom. While us humans use it to spice up our sex lives, a new study has found that male nursery-web spiders don't have much of a choice - they either tie up their mates, or fall victim to sexual cannibalism (which is a total mood killer tbh).
Female nursery-web spiders (Pisaurina mira) love nothing more than making a snack out of their partners immediately after sex. Though sexual cannibalism is probably the sexiest form of cannibalism out there, male nursery-web spiders would rather live to see another day. So, in order to do so, the males must tie up their female partners before they mate with them, researchers from the University of Nebraska have found.
First off, why would a female spider want to kill her mate anyway? As one of the researchers, Alissa Anderson, told LiveScience's Mindy Weisberger, "[T]o a just-fertilised female with eggs to nourish, her mate's immediate value transforms from sex partner into 'resources for her developing offspring'."
Basically, the female's mind snaps from one thing to another. When a male first approaches, she sees him as a way to fertilise her eggs (spiders aren't very romantic). But as soon as the deed is done, she sees him as a great source of food, because now she has to support a bunch of spider babies. It makes sense on a very primal level, despite how the male - or our delicate human sensibilities - may feel about it.
A male nursery-web spider restrains a female during sex by wrapping silk around her legs. Credit: Alissa Anderson
Anderson and her colleagues were able to observe this odd mating ritual in the lab by pairing up female nursery-web spiders with males that could spin silk, and males that had their silk-spinning ability blocked. Both sets of males were often able to mate with females, but those that couldn't tie up their female partners died immediately after.
While both male and female nursery-web spiders can produce silk, they never use it to catch prey like other spiders. Instead, like their name suggests, the female uses it to make a home for her offspring. In other spider species, males will sometimes drape females in silk to mate with them, but nursery-web spiders are so far the only species to use the substance as a restraint.
In fact, Anderson says, male nursery-web spiders have longer legs than the females - a trait that might have developed through sexual selection, since males with longer legs often live on, while males with shorter legs become dinner.
Understanding these strange traits will hopefully shed light on how these spiders evolved, and might also give us the tools to understand some of nature's other bizarre mating rituals.
You can read the team's full report in Biology Letters.