These kinky male spiders could star in 'Fifty Shades' for arachnids
Male nursery web spiders give Christian Grey a run for his money, but only because they like to continue living after they've enjoyed a little romp.
"In sexually cannibalistic animals, male fitness is influenced not only by successful mate acquisition and egg fertilization, but also by avoiding being eaten."
That wonderfully obvious statement kicks off the abstract of a paper published online Wednesday in the journal Biology Letters. Two researchers from the University of Nebraska, Alissa Anderson and Eileen Hebets, studied the male nursery web spider (Pisaurina mira). They wondered if the creature's elongated legs and its penchant for tying up its female mates before copulation came about as a result of its desire to, indeed, avoid being eaten.
To test out their theory, the researchers blocked the spinnerets on a group of male spiders using dental silicone. This prevented the males from tying up their female mates before copulation.
Sure enough, when compared with a group of spiders in the test that didn't have their spinnerets blocked, the males who couldn't spin the silken ties were devoured after sex seven times more than the males who could bind the females.
Also, the males who could tie up their mates were nearly seven times as likely to have two insertions in which they could deposit sperm. (See video below.) The researchers believe this might help ensure fertilization by either transferring more sperm, or diluting or washing out sperm from previous mates.
The male's longer legs in comparison to their bodies, known as size dimorphism, is believed to be a powerful ally in this unusual mating behavior. They can use their longer legs to test out the interest of potential mates from a distance and then bind them in silk.
The researchers also discovered that males had a harder time wrapping up females that had previously had sex. Virgin spiders allowed the binding process to happen without resistance. This suggests that female nursery web spiders don't necessarily buy into the whole silk bondage thing, but that because it's evolved as a mating strategy for the males they are obliged to go along with it.
"This study provides strong evidence that size dimorphism and copulatory silk wrapping have been sexually selected through fitness benefits to males, but the putative fitness cost(s) of these traits for females remain unknown," conclude the authors of the paper.
The nursery web spider is of course not the only arachnid that risks, or even gives, its life for the chance to reproduce. The black widow famously does the same. In that species, the male must position himself between the female's fangs to get into proper mating position. Sometimes, that doesn't end so well. Male wasp spiders are also often devoured by their mates, after they break off their own genitals and leave them behind in their female partners. In the case of the male jumping spider, he might not even get to copulate before he's devoured. If his intended doesn't like his mating dance, she sometimes just kills him and eats him.
So it's no wonder male nursery web spiders have taken to restraints. It's actually surprising that there aren't more spiders into bondage. Maybe after they watch this spider porn film...