Male spiders, at risk of being eaten by females, have developed a clever escape stunt: They shoot themselves in the air after sex.
When Shichang Zhang observed this phenomenon in a sample of a rut orb of a species Philoponella prominensThis was the first ever observation of a male spider ejaculating itself to avoid sexual cannibalism. Zhang, who is an ecologist at China’s Hubei University in Wuhan, wrote in an email that he was surprised to see the behavior in the lab.
“Animals typically use this ultra-fast movement to evade enemies or to capture prey, but not as a defense against a sexual partner.”
In the study by Zhang and colleagues, which was recently published in the journal current biology, All males who ejaculate themselves in the air survive mating. Recordings from high-speed cameras showed that the males, roughly the size of a letter on a computer keyboard, rotated at a rate of 175 times per second during the escape maneuver.
The researchers “provide compelling evidence that this remarkable behavior is a sexual adaptation,” said spider scientist Greta Benford of Lewis and Clark College in Portland, Oregon, who was not involved in the study. “I don’t know of any studies that have shown this before.”
A meal date – literally
There are about 290 species of orbweb spiders worldwide. In China , P. bromine It is often found in gardens, fields and forests. They live in colonies of three hundred or more spiders. Binford, who has done research on orbweb spiders in Peru, describes their home as an “apartment complex, where each spider has its own wheel-shaped web, which is attached to the other by a single pair of scaffolding parts.”
Female orb spiders, like the females of many other spider species, try to eat their sexual partners after mating. Perhaps they do this because the males are smaller and easier to catch than other prey. The male approaches the female cautiously for mating. It uses special organs, called “walkers,” to insert the semen sac into the female’s genital opening. Then the male jumps at lightning speed.
Zhang and his colleagues collected small spiders from a nearby garden and raised them in isolation in the lab to study their catapult behavior up close. The team then placed a male who had never mated into an equal virgin female network, and looked at the interactions between the animals. In doing so, the researchers made sure that the female had enough fruit flies to eat so that hunger did not play a role in how she interacted with the male.
The team repeated the experiment with 180 pairs of spiders and observed 155 successful matings. In 152 cases, males were able to fertilize the female and then jump unharmed toward freedom. In the three cases where the males failed to fling themselves away in time, they were caught, killed, and eaten by the female.
In a separate series of experiments, researchers looked at the effects of adaptation on males’ escape abilities. For example, they investigated what happened if males stripped two of their front legs. The researchers found that, like males who did not escape in time, these handicapped males turned out to be literally when the females were eaten.
Put the best foot forward
Looking at the high-speed camera frame by frame, Zhang said, the research team was able to “unravel the secret of the catapult.”
The team found that the core sits at a joint in the spider’s shin, or tibia, of the front leg. During mating, these front legs cross the female’s. When the male is ready, he contracts a muscle in his pectoral head, which pushes the hemolymph (the spider’s blood version) into his front legs and naturally pushes it away from the female. ‘It’s like a balloon with little arms; Benford explains that if you squeeze the balloon, the arms will pop out.
The males also make a safety line (of silk) that they end up in their web again, at a considerable distance from the female. This wick is a precaution, Zhang says, “in case the female is aggressive and suddenly comes to kill him.”
When the researchers cut this safety line during the experiment, the fleeing males ended up not in their nets, but on the ground. They then court the female, but do not attempt to mate with her. This is presumably because the male knows that after mating he cannot escape without his safety line. That’s why he doesn’t dare, says Zhang.
But why does he flirt with the female if he does not intend to mate with her? Female scientist Eileen Hebbits of the University of Nebraska, who was not involved in the study, says a female may not try to eat it right away as long as she still sees it as a potential mate.
Strange defense tactics
In the spider world, males use all kinds of “weird” tactics to avoid being eaten, says Hibbits. Some males, she adds, wrap females with silk threads to transport semen, or present women with a silk-wrapped “gift”, supposedly as a distraction.
But there are also males who make the ultimate sacrifice to pass on their genes. If the male manages to mate with her and then stays nearby to be eaten, the female is so satiated that she does not look for other males and rears the brood of her eating mate.
In the words of Hebbits, Zhang and his team’s research is “another wonderful example of the nearly endless possibilities available to committed, curious, and enthusiastic scientists about discoveries in arachnids.”
This article was originally published in English at nationalgeographic.com