Spider courtship is a risky business. In some species, females routinely decide that they would rather eat a male than mate with him, and researchers have struggled for decades to understand why. A recent experiment with a type of Spanish wolf spider suggests that the reason may depend on the spider's personality.
A virgin spider cannot be sure how many chances she will have to mate. Every male could be her last, and if she eats all of them, she will never reproduce. Why would a spider take this risk? One possibility is that females are choosy, holding out for large, healthy males with good genes and devouring the rest. Another possibility is the aggressive spillover hypothesis, which suggests that some females have strong predatory instincts that spill over into aggression toward potential mates. These females might eat males even when they would be better off mating with them.
To learn more about cannibalistic spiders, researchers at the Experimental Station of Arid Zones in Spain and their colleagues caught 80 juvenile females of the species Lycosa hispanica—a type of wolf spider—and fed them as much as they wanted while they matured. Some females put on weight more quickly than others. “Since all females had similar prey availability, we estimated that female growth rate would be the result of female voraciousness,” says Rubén Rabaneda-Bueno, the study's lead author.
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After each female molted to adulthood, the researchers placed a male in her enclosure. Females that ate their suitors were offered additional chances with new males. Most of the cannibal females were choosy. They ate males that were in poor condition and mated with males that were of high quality. “But we found that there were a few females that would consistently get a male and kill it and get another male and kill it—so they were really aggressive,” says Jordi Moya-Laraño, the study's senior author.
The most aggressive females killed big, healthy males as often as they killed scrawny ones. The same females also had the highest growth rates, indicating that they were the most aggressive toward prey. “In this study, a female personality trait—her voracity toward prey—was correlated with her aggressiveness toward males,” Rabaneda-Bueno says. “Our results provide evidence that different female personalities can lead to different outcomes in the interactions between males and females in a sexual cannibal.”