We all know where the black widow spider gets its name – the female will devour the male right after they mate. Some male spiders however are not very pleased with this arrangement, in particular those from the Thanatus fabricii species. In order to survive the act of procreation, the males will bite and tie up the females before mating.
Coercive behavior in mating is not uncommon in the animal kingdom, but it is extremely rare in spiders, since females are usually physically superior. In this particular case however, the coercion is a matter of survival for the male spider. In fact, the males will never mate with a female unless it has been bitten and immobilized. This means that without this behavior, the species would go extinct.
Researchers wanted to know more about the mating habits of this spider species so they gathered male and female Thanatus fabricii and started running experiments. What they’ve noticed is that the mating ritual starts with the males first biting the females on the legs. The females would then draw the legs to the body and become paralized. The mating rituals of other spider species can take hours, but for these spiders, they were very short.
Once the female was immobilized, the male would mount it and bind its legs and body, before inseminating it. Once the mating was complete, the female would remain motionless for some time before freeing itself from the males silk.
Furthermore, after mating, researchers observed that the females were less successful in catching prey, and they were less mobile. This suggested that the mating process injured the female in some ways.
Female Thanatus fabricii spiders are larger than males, so this mating strategy serves two purposes for the male: surviving the encounter, and overcoming the female’s resistance to mating. It’s important to keep in mind that sexual cannibalism is quite common in spiders and other invertebrate species where the female is larger than the male.
However, this strategy is not 100% effective. In 11% of the mating cases, the females were able to attack the male and consume it before copulation. Researchers are still exploring other scenarios as well, in which the females are not actually completely immobilized by the male, with their inactivity being a signal that they have become receptive to the male’s advances. To further this case, there were situations where the female continued struggling through the ritual and thus rejecting the male and denying the mating act.