A new study led by Hubei University has found that, after males of the orb-weaving spider Philoponella prominens mate with a female, they use a joint in their first pair of legs to quickly undertake a split-second catapult. The spiders launch themselves away from their sexual partners at high speeds reaching up to 88 centimeters per second. According to the experts, they do this in order to avoid being eaten by the female in an act of sexual cannibalism.
“We found that mating was always ended by a catapulting, which is so fast that common cameras could not record the details clearly,” said study lead author Shichang Zhang, an associate professor of Life Sciences at Hubei University.
Professor Zhang and his colleagues made this fascinating discovery while studying sexual selection in this species of spiders, who live in rather large groups of up to 300 individuals. Of the 255 successful couplings that the scientists observed, 152 ended with male catapulting, which all managed to survive their sexual encounters. The other three males were killed and eaten by the females.
Using high-resolution cameras, the researchers calculated an average peak-speed of catapulting spiders of approximately 65 cm/s, and an acceleration of about 200 m/s2. While soaring through the air, the males spin around 175 times per second. In order to perform such impressive feats, the spiders initially fold their tibia-metatarsus joint against the female. At the moment they release it, hydraulic pressure allows for extremely rapid expansion.
“We observed that males that could not perform the catapulting were cannibalized by the female. It suggests that this behavior evolved to fight against female’s sexual cannibalism under strong predation pressure of females,” Professor Zhang explained.
“Females may use this behavior to judge the quality of a male during mating,” he added. “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 research, the scientists aim to explore the role that the catapulting abilities of male spiders may play to ensure mating success.
The study is published in the journal Current Biology.
By Andrei Ionescu, Earth.com Staff Writer