Spider sex is a curious and often brutal thing. Unlike the emotional performance of human intercourse, arachnid mating is very much a functional affair, and regularly brings grisly consequences for the participants, which have been observed cannibalizing or tying each other up after doing the business. Last year, researchers found evidence that one species of orb-web spider even performs female genital mutilation (FGM) after copulating, and it seems that this was not a one-off, as another species has now been found to do the same.
Publishing a study in the journal Biology Letters, Kensuke Nakata from the Kyoto Women’s University describes how she collected virgin female orb-web spiders belonging to the species Cyclosa argenteoalba from bamboo forests around Osaka and Kyoto. These specimens were confirmed as virgins as they were all in the process of molting, which occurs as they make their transition from adolescence to adulthood, and before which they do not mate.
These spiders were then paired with males and allowed to mate. After, the study authors inspected their genitalia, known as epigynum. This includes an appendage called a scape, and in 90 percent of cases, females were found to have had their scapes cut off following their first copulation with a male.
According to previous research, male spiders use the scape to help them mount females, clasping onto it in order to be able to insert their sperm. By removing the scape, therefore, it is thought that males ensure that females can no longer successfully mate with rival males. In doing so, they ensure that they alone are able to pass on their genes by mating with a given female.
The scape of the female is cut off after copulation. Kensuke Nakata
Further observation revealed that none of the mutilated females were able to mate with other males once their scapes had been cut off, highlighting the effectiveness of the technique. Many other spider species are known to engage in practices designed to prevent the repeated mating of females, yet few of these techniques are as successful as this particular form of FGM.
For instance, some male spiders break off parts of their own genitalia in order to “plug” that of the female, yet this comes at a greater cost and produces less favorable results than simply removing a partner’s scape.
Interestingly, female spiders continued to respond to courtship from other males even after undergoing FGM, and often attempted to mate again, yet always unsuccessfully. While it is not yet clear why this occurs, Nakata suggests that it may be because the scape contains no sensory nerve endings, meaning females might not actually be aware that they have been mutilated.
Speaking to National Geographic, Nakata explained that this study indicates that, rather than existing in just one species of spider, FGM is probably “widespread in orb-web spiders.”