Certain orb-weaving spiders have developed a catapult-like mechanism to spring to safety and avoid sexual cannibalism, an international research team reports April 25 in Current Biology.
Hubei University behavioral ecologist Shichang Zhang, the study’s first author, says that the researchers first observed the post-mating catapulting behavior during field studies in 2019. This species of orb-weaving spider—Philoponella prominens—lives in colonies of up to 300 individuals, although each spider maintains its own web within the colony.
After witnessing the odd behavior in the wild, Zhang and colleagues brought the spiders into the lab for a closer look. Using high-resolution cameras, researchers recorded males—which are less than a centimeter long—catapulting away from the female at speeds up to 88 centimeters per second (a little over 3 kilometers per hour). The spiders achieved these impressive speeds by folding their first pair of legs against the female during mating and rapidly straightening them, vaulting into the air as soon as mating was complete.
Researchers also demonstrated that this is an essential anti-cannibalism strategy for males. Out of 155 matings, all but three males performed this catapulting behavior. All of the catapulters survived, while all of the non-catapulters were unceremoniously eaten after mating. When scientists prevented males from performing their post-mating catapult by placing a fine brush behind the spiders’ backs, every one of these spiders met the same untimely demise. Intriguingly, when one or both of the front legs were removed, or when the joint itself was damaged, males chose not to mate; they courted but did not mount females.
“Every male, when he’s approaching a female with the objective of mating, runs the risk of being a meal rather than a mate,” says Catherine Scott, an arachnologist at McGill University in Canada who was not involved in this research. In light of this, various spiders have developed different techniques to avoid sexual cannibalism, such as wrapping the female in silk or mating with immature females.
This study, says Scott, “is really exciting because it's a completely new way for males to solve this problem.”
Zhang says researchers don’t yet know exactly how this behavior affects males’ overall reproductive fitness. Since both males and females can mate multiple times (and multiple couplings between the same partners also occur), a male that is proficient at catapulting may be able to mate more times than less-proficient or non-catapulting males, and therefore may be more successful at passing on his genes, the authors suggest. In future experiments, Zhang says, researchers hope to determine, “whether there is a correlation between kinetic performance of a male and its reproductive success.”