This story appears in the December 2018 issue of National Geographic magazine.
When seeking sex, why wouldn’t the male Latrodectus geometricus spider go for the nice young females? They’re more fertile than their elders. They’ll mate more quickly, without an elaborate courtship. Last but not least: Young L. geometricus females don’t cap off a copulation by cannibalising their date—while older females do. (That’s what gave the species its common name: the widow spider.)
Given the obvious advantages, a research team in Israel expected L. geometricus males to prefer young females. To test that assumption, researchers set up spider orgies, offering males access to consorts of all ages. Their findings were published in Animal Behaviour.
To get sex with an older female, a male might fight off many rivals or perform courtship gestures for up to six hours. At the magical moment, he’d place one of his two sexual organs into one of her two sexual openings—and she would start to eat him alive. If he survived, he might try to mate again or be too maimed to do so.
In the study, when males had one-on-one time with females of different ages, the males mated with fewer than half the youngest females—but 100 percent of the oldest ones. Not one of the males that mated with the youngest females died from cannibalism—but more than half those that mated with the oldest females did. “We really don’t understand” males’ suicidal lust for older mates, says study co-author Shevy Waner. One theory is that mature females exude stronger sex pheromones, compensating chemically for what they lack in fertility and youth.