A new study reveals that Philoponella prominens are social spiders, meaning they live in groups, but soon after mating, the male spider has to quickly jump away to avoid being eaten by his female partner.
They are making their homes in the forests of central China in places like Hubei, Hunan and Jiangxi provinces, according to study author Shichang Zhang, associate professor at Hubei University in China.
Other spider species, such as the red spider, practice cannibalism sexually, but this is the first report of spider species using ultra-fast actions to escape from eating their partners.
The researchers examined 155 successful maturation processes in a laboratory setting. In 152 of the mating cases, the male spiders were able to jump away to safety, while the three males who were not eaten by their partners.
“Their ability to sense danger is low, or they are cumbersome during mating, or they cannot perform a catapult,” Zhang said of the three spiders that did not jump to safety.
Using a high-speed camera to capture acrobatic movements, the scientists determined that male spiders press their front legs against the female, then push quickly to release hydraulic pressure and reach speeds of up to 34.5 inches per second (88 centimeters per second) to escape.
Spiders can also spin up to 469 revolutions per second while jumping away to avoid sexual cannibals, according to the study.
“I think the main reason for this is the escape of the female, the ejaculation and spinning makes it difficult for the female to catch her,” Zhang said.
The study found that if the researchers removed one or both front legs, the male spiders courted potential mates but made no attempts to mate, meaning that both legs were necessary for successful mating.
When Zhang’s team prevented some male spiders from being able to ejaculate away, all of those spiders were eaten by their female partners, leading the researchers to believe that ejaculation was a necessary survival skill.
Female spiders choose sperm
The mating was ended by the female spider, Zhang said, and as soon as the male partner felt his counterpart’s aggression, he jumped to safety.
It’s not known why female Philoponella prominens tries to eat male spiders after mating, Zhang said, but it may be a sexual selection test to assess whether males are worthy of reproductive partners.
Unlike mammals, the female spider has a sac in the reproductive tract called the seminal vesicle that holds the sperm and prevents them from meeting the egg. After the male injects the sperm into her body, Zhang said, she keeps it there until she decides whether to use it.
If she wanted to use it, she would pressurize the sperm from the sperm to fertilize the egg, he said. If she doesn’t want to, Zhang added, she can take the sperm out of her body or change the acidity level of the sperm to kill the sperm.
“The female may accept sperm from the male that can ejaculate but drain the male’s sperm that she can easily catch,” he said.
In a community network, female Philoponella prominens rarely leave, while their male counterparts venture into other networks to mate and can mate with one female spider up to six times before moving on to another, Zhang said.
The study found that male spiders attach themselves to the end of a safety line of silk threads at the edge of a female partner’s web before mating and use them to help escape as well.
When the researchers cut the safety line during mating, they noticed that the males still ejaculated away, but would fall to the ground instead of climbing up to the safety line, according to the study.
Male spiders often repeat the mating behavior, Zhang said, jumping away and then crawling back to the same female to mate again.
In the future, Zhang would like to investigate whether there is a link between the catapult ability of male Philoponella prominens and their ability to reproduce successfully..