Ah, love. It makes the world go ’round. But as we all know, love can also spell trouble – especially if you’re a spider. That’s because, in many spider species, after the reproductive act has been fulfilled, the female will promptly eat the male and be done with it.
Thankfully for the males of the orb-weaving spider Philoponella prominens, however, they have managed to evolve a smart evolutionary quirk that helps them avoid the jaws of their reproductive partner.
Described in detail for the first time in a new study in Current Biology, these male spiders use a joint in their first pair of legs to immediately undertake a split-second, daring catapult action, flinging themselves away from their partners at impressive speeds clocking up to 88 centimetres per second (cm/s).
“We found that mating was always ended by a catapulting, which is so fast that common cameras could not record the details clearly,” says study co-author Shichang Zhang of Hubei University in Wuhan, China.
It’s a daring and acrobatic act that helps these males circumvent the act of sexual cannibalism, and preserve themselves for future reproduction.
The few hapless males who didn’t catapult were promptly captured, killed and consumed by their female partners. When the researchers prevented males from catapulting, they met the same fate.
Zhang and colleagues made the discovery while investigating sexual selection among the spiders, which live in communal groups of up to 300 individuals. Of 155 sexual partnerships they witnessed, 152 ended with a male catapulting and surviving to tell the tale. The three males that didn’t catapult, however, were killed, and the 30 further males they prevented from catapulting also got eaten.
With high-resolution video cameras, the researchers calculated an average peak speed of catapulting spiders of about 65cm/s. Speeds ranged from about 30cm/s to almost 90cm/s. As they soar through the air, the males also spin around 175 times per second on average.
So how does this clever leg joint work? Well, the males fold their tibia-metatarsus joint (for reference, in humans, that’s the equivalent of the joint between our shin bone and the foot bones) against the female. When released, the joint releases hydraulic pressure that allows for rapid expansion.
“We observed that males that could not perform the catapulting were cannibalised by the female,” Zhang says. “It suggests that this behaviour evolved to fight against female’s sexual cannibalism under strong predation pressure of females.
“Females may use this behaviour to judge the quality of a male during mating,” he adds. “If a male could not perform catapulting, then kill it, and if a male could perform it multiple times, then accept its sperm.”
In future studies, the team hopes to explore the role of catapulting ability in male mating success.
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