Spider ladies love their lovers to eat! In order not to end up as a meal after sex, the males of an Asian spider species have developed a sophisticated catapult mechanism, researchers report: if their partners become biting, they push off from them by somersaulting – secured by a leash. The scientists explain that this is an astonishingly complex system that developed in the course of the battle between the sexes in this species of spider.
It is snapped, flicked, thrown…: Numerous lightning-fast behaviors and techniques are known from the animal world. They are often based on the storage of elastic energy, which can be released suddenly when needed – like a catapult. Many of these mechanisms are used to catch prey or to protect against predators. But the current study by researchers led by Shichang Zhang from Hubei University in Wuhan now shows a previously unknown purpose of animal speed mechanisms: They can apparently also be used to escape from sexual cannibalism.
This reproductive behavior is known from some species of insects and spiders. The most famous example is probably the black widow, who even owes her name to her penchant for eating her lovers after mating. In some species, the males willingly submit to this fate, because in this way they strengthen the partner for the production of the common offspring. In other species, however, the males try to escape their rabid ladies.
Bizarre sex life in sight
This is apparently also the case with the orb-web spider Philoponella prominens. When observing this species, the researchers noticed that the males often shoot straight out of the web after mating. So they devoted a more detailed investigation to this phenomenon. To do this, Zhang and his colleagues used high-speed cameras to target pairs of spiders and also conducted experiments on the males to better understand the basis of the mechanism.
It turned out that after mating, the males push off their partner with a sudden movement of their front pair of legs. The folding movement triggered by a joint accelerates them enormously to speeds of up to 88 centimeters per second. They also flip 175 times per second. As the researchers report, the eight-legged acrobats are secured by a spider’s thread during the action. The scientists observed that they then often climb back to the female spider to mate with her again.
Spider-Men have to be quick
That the behavior actually serves to escape from cannibalism initially emerged from the observation of three males who apparently had ignited too late: they were eaten by their females. The researchers then confirmed the importance of the procedure through experiments: they blocked the front legs of 30 male spiders. It turned out that none of these handicapped animals managed to escape after mating and so they ended up in the stomachs of their “ladies”. “It turned out that males who don’t master catapulting are always eaten by the females,” says Zhang. “This suggests that this behavior evolved in response to the intense predation pressure exerted by females.”
Further investigation results of the researchers revealed that the amazingly effective catapult mechanism of the spider men is not based on muscle power, but on a hydraulic effect. Because, as they explain, the joint in question has no extensor muscles. Eating city food, the animal apparently triggers a mechanism that induces movement via the release of hydraulic pressure. The tibia-metatarsus joint, which the male spider previously angled against the female’s body, is suddenly stretched.
According to Zhang and his colleagues, the concept is an intriguing development in the battle of the sexes in spiders. In this case, however, the female may also benefit: “Perhaps she uses this behavior in a certain way to assess the quality of a male during mating,” says Zhang. “If it doesn’t have good catapult skills, kill it. But if the male masters it several times and keeps climbing up to her, she might end up willingly accepting his sperm,” says the biologist. In order to confirm this assumption, he and his colleagues now want to examine more closely the role of catapulting ability in the mating success of the males.
Source: Cell Press, Article: Current Biology, doi: 10.1016/j.cub.2022.03.051
The video shows a male spider repelling a female during mating. © Shichang Zhang