Some spiders catapult away after sex to avoid death

This handout photo provided by Shichang Zhang of Hubei University on April 25, 2022 shows two Philoponella prominens spiders mating.

Sometimes there are pretty valid reasons to leave right after sex.

A team of Chinese scientists has found that male orb-weaving spiders hurl themselves away from their mates, pulling 20 Gs of gear to avoid being killed and eaten by females.

The mechanism, first described in the journal Current Biology on Monday, involves the spiders’ first pair of legs to immediately take a split-second catapult action.

Lead author Shichang Zhang of Hubei University in Wuhan told AFP he was “excited” to make the discovery, which would require high-speed, high-resolution cameras to detect.

Zhang and colleagues studied sexual selection in this spider, “Philoponella prominens,” which lives in communal groups of up to 300 individuals.

Of the 155 successful matings, they found 152 ended up catapulting the male and thus survived the encounter.

Males can mate up to six times with the same female: they bounce, climb back up using a silk safety line, mate, and bounce back again.

The three males that failed to catapult were promptly captured, killed and eaten by their mates.

Another 30 men who couldn’t slingshot by placing a fine brush behind their spines all suffered the same fate — leading the researchers to conclude that slingshotting is essential to prevent sexual cannabalism.

A male spider that shoots off a female during mating. Credit: Shichang Zhang

“Currently, I don’t know if there is another species that can do the catapulting as well,” Zhang said, adding that he planned to investigate further.

Sexual predation by females is observed in many species of spiders, with different strategies to avoid it: for example, male maternity web spiders tie up their mates before mating.

A suitable partner

The escaping orb-weaving spiders clocked up some impressive statistics: Their average peak speed was 65 centimeters per second, with an acceleration of 200 meters per second squared. That is equivalent to 20 Gs, or 20 times the acceleration felt during a free fall.

As they soar through the air, the males spin at about 175 revolutions per second.

The males catapult by folding the tibia-metatarsus joint of their first leg pair against females. When released, it applies hydraulic pressure and causes the legs to expand.

Zhang said he believes the females judged the males’ sexual fitness by their ability to escape.

“The catapulting allows a man to escape female sexual cannibalism, and a woman can choose high-quality men because the kinetic performance can directly correlate with the man’s physical condition,” he said.

Even though they’ve already mated, females may only accept sperm from males who have passed the test, Zhang explains.

Spiders differ from mammals in that females have a structure known as spermatheca, where deposited sperm are stored. They can decide whether to use it to fertilize eggs, or reject it by squeezing it out or changing the pH to kill the sperm.

Future work will confirm whether there is a link between male catapults and reproductive success, Zhang said.

These male spiders catapult at impressive speeds to flee their mate before being eaten

More information:
Shichang Zhang, Male Spiders Avoid Sexual Cannibalism with a Slingshot Mechanism, Current Biology (2022). DOI: 10.116/j.cub.2022.03.051. … 0960-9822(22)00485-7

© 2022 AFP

Quote: Must bounce: Some spiders catapult away after sex to avoid death (2022, April 30) retrieved Aug 24, 2022 from .html

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