Researchers in China have described yet another freaky sex habit of spiders (as if there weren’t enough already): Some male spiders launch themselves at great speed off their cannibalistic female partners, to avoid being eaten after copulating. The way they make their egress is similar to the mechanism at play in catapults, according to the new study.
The spiders are communal orb-weaving spiders (Philoponella prominens), and they have active and potentially fatal sex lives. Like praying mantises, the female arachnids have an appetite for their sex partners. But the 0.12-inch (3 mm) males of the species have developed an escape plan: They capitalise on an adaptation in the joint in their front two legs to launch themselves off the females, at speeds of nearly 3 feet (88.2 cm) per second. The team’s research is published today in Current Biology.
“Males can use super-fast actions with extraordinary kinetic performance to escape the female’s attack,” said Shichang Zhang, a behavioural ecologist at Hubei University, in an email to Gizmodo. “This may help scientists to consider the balance or trade-off between cost in physical strength and the benefit of paternity when studying sexual conflict.”
There are many other methods male spiders use to counter sexual cannibalism, Zhang said, including nuptial gifts, pretending to be dead, and cutting off their own genitals or mutilating the females’; they’re as cutthroat as they are creative. But the catapulting approach is new to the researchers.
In a lab, the team mated 155 pairs of spiders; in 152 of the encounters, the males catapulted off the females to safety. The three males that did not do the behaviour were captured, killed, and eaten by the females.
The researchers attributed the males’ ability to launch off their sexual partners to a leg joint called the tibia-metatarsus. The tibia-metatarsus (and all the leg joints in the spiders) are ensconced in sheathes called thecae, which increase the limbs’ elasticity. In the front two legs of the male spiders, the surface area of the thecae was much larger than on the other legs.
These spiders don’t have sex like quite humans: Mating lasts about 30 seconds, and male spiders use an appendage called the palp to inject sperm into the female’s epigynum, a hard plate on the bottom of the abdomen.
The females’ eggs aren’t immediately fertilised. Instead, the female can store sperm and only release the egg for fertilisation when it is ready. It can also squeeze the sperm out or kill them if the sperm (and the male who provided them) are found wanting.
“Mating is ended by the female; once [they] sense the aggressiveness of the female, males catapult off, but if a male can not sense the danger, it may not catapult before the female kills it,” Zhang said.
“Through the catapulting, male can escape female sexual cannibalism, and female can choose males with high quality, because the kinetic performance may directly correlate with male’s physical condition. Only those with good quality can catapult off far or can catapult for several times,” Zhang added.
The team also observed that the males employed a silk ‘safety line’ to dangle near the webs where the mating occurred, which they believe was a means for the male to return in case they wanted to attempt mating again. On a human scale, according to Zhang, the action is equivalent to a 1.52 m-10 human leaping a third of a mile from their partner after sex. You know, to be safe.
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