(Photo: João Coelho)
Iberian tarantulas are a lot like your ex-girlfriend: they get close to you, then brutally betray you, leaving you emotionally wrecked for life. But Iberian tarantulas go even further. They frequently kill and eat males right after mating with them. Why?
Scientists aren't sure, but they have three hypotheses. Nala Rogers of Scientific American summarizes them:
- She’s choosy. She wants to mate, but not with the male in front of her, so she holds out for someone better. In the meantime, hey, free meal.
- She’s just hungry. “It doesn’t matter if you have a great father for your offspring if you’re going to die tomorrow. If you’re starving, eat him,” says Jonathan Pruitt, assistant professor of behavioral ecology at the University of Pittsburgh, who has studied cannibalism in funnel-web spiders.
- She has terrible impulse control. A successful spider is a voracious predator. The more she eats, the more resources she can devote to making big, healthy egg sacs. But aggressive tendencies that help with hunting might not be so helpful in other contexts. If a spider is just generally vicious, her aggression toward prey might spill over onto potential mates in what is known as the “aggressive spillover hypothesis.”
Researchers at the Experimental Station of Arid Zones in Spain performed experiments to study the behavior of female sexual cannibal spiders. Like your "friends" who set you up with that girl in the first place, they placed male spiders in cages with female spiders and observed their behavior. Here's what happened:
Most females mated with the first male who came calling. Some ate him instead. Females who ate their suitors were offered additional chances with new males.
Most of the cannibal females were choosy. They ate males who were in poor condition and mated with males who were 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. This is evidence that aggression is consistent between foraging and mating contexts,” 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.”
-via Dave Barry