Spider Sex: Sadistic, Yet Effective

Reproduction is a violent affair for a spider discovered in Israel. The aptly named Harpactea Sadistica employs a mating technique called “traumatic insertion,” whereby the male pierces the female’s body with his fangs and then injects sperm directly inside. Traumatic insertion occurs in other insects, like bed bugs, but this is the first time it’s been observed in spiders.

When most spiders mate, the male ejects sperm into the female’s genital organs, and the sperm is then stored in a pouch called the spermatheca. She releases the sperm later to fertilize eggs in the uterus—so the last male to mate with her will most likely father her offspring.

In H. sadistica, however, the eggs are fertilized in the ovaries and develop into embryos before being laid. This means that the first guy to put the (sadistic) moves on her is most likely to fertilize her eggs. Co-evolution seems to be at work: Males have needle-like sex organs that enable them to grip females and directly insert the sperm, and females have atrophied spermathecae. Milan Rezac, from the Crop Research Institute in the Czech Republic, reported the findings in the journal Proceedings of the Royal Society B.

As the BBC explains:

Like many spider mating rituals, H. sadistica 's approach follows an elaborate pattern, with the male tapping the female, subduing her, and wrapping himself around her to properly position the sex organs (above). He then alternates between the two, piercing and injecting the sperm on one side, then the other, forming two neat rows of holes in her abdomen.

While traumatic insertion might strike us as weird, sex in the spider world can be rather, er, extreme.

"Numerous bizarre adaptations are known in spiders for males to maximise reproductive fitness," says Rezac, which makes them perfect subjects for investigating the evolution of extreme mating tactics. "These range from common practices such as mate guarding and the use of sperm plugs, to self sacrifice and spontaneous death after copulation," he says.

Sperm competition may have spurred the evolution of this brutal mating method in H. sadistica, but Rezac says more research is needed before he can pin down the explanation.