If your partner is likely to devour you after sex, snapping off your genitals inside her might seem a reasonable reproductive strategy. This game plan is used by males of the orb-web spider Nephilengys malabarensis and, it turns out, continues to work in their favour, regardless of whether they survive the encounter.
Thus begins my new piece for Nature News. Honestly, I can’t believe they let me keep the lede. Here’s more:
Daiqin Li at the National University of Singapore and his colleagues studied the species and found that after the male breaks away his severed organ continues to pump sperm into the female. This allows him to fertilize her remotely, while denying entry to other males. Even though the male cannot regrow his genitals and so renders himself sterile, he increases the odds that he will father the offspring of his one and only mate.
Male spiders deliver their sperm through a pair of structures known as palps, which are found on the sides of their heads. By serving sexual encounters between 25 pairs of virgin N. malabarensis, Li’s group found that every coupling ended with damage to the male’s palp. In 12% of cases it was partially severed; in the rest it snapped off completely.
Li thinks that this bizarre strategy, found in only two spider families so far, evolved to counter the female’s penchant for cannibalism. “The females are very aggressive and 75% of them kill the males during sex,” he explains. “The duration of copulation is also very short, and the females initiate the break-off.”
By dissecting the mated spiders, Li and his co-workers found that the palp has dispensed only about one-third of its sperm by the time the female pushes the male off. But it continues to transfer sperm after it breaks off, and does so at a faster rate.
And head over there for the rest of the story.
(In the picture at the top, the bigger female devours the smaller male while his palp clings on to her underside (in the red box).)