Spiders Detect Cannibalistic Females by Web

To avoid becoming lunch, male black widow spiders (Latrodectus hesperus) seem to assess the likelihood of females cannibalizing them before approaching a web to mate, according to a set of experiments featured in the journal Animal Behaviour.

Arizona State researchers found that males used chemotactile cues on females' webs and silk to assess whether they recently caught food or if they're well-nourished. Acting selectively plays to males' advantage since well-fed females show more interest in mating and are less likely to consume their sexual partners when compared to starving females.

The black widow's namesake derives from females' occasional trick on males: As a male spider approaches a female in her web to court her, she'll eat him instead. Researchers have observed females cannibalizing males after copulating, but not much beforehand until now.

If female spiders are hungry, they'll skip sex altogether to eat males, especially if there's a surplus of them. This is why courting behavior in black widows is particularly extensive -- males not only have to maneuver around the web to show they're not prey, they also must demonstrate why females should reproduce with them.

But the experiments show that males don't blindly crawl into just anyone's home. In one setup, virgin males were placed within proximity to two types of empty webs: those of well-fed females and those of starving females.

Through chemical and architectural cues on the webs alone, males began courting on the webs of well-fed spiders more often than starving ones, just as the team hypothesized.

It's unclear what exactly prompts male behavior, but scientists suggest signs of recently struggling prey and traces of chemicals during foraging give males a better idea of what they're getting themselves into. Web architecture provides clues too, as well-fed females tend to build wider webs while less-nourished ones have smaller webs with stickier silk.

Next, researchers did the same experiment but this time with females present. Still, males approached the well-fed gals more often for mating -- for good reason, too. Zero well-fed females attacked the males before sex, while some 70 percent of starving spiders did.

A third experiment switched the females and their webs, presenting males with well-fed females on starved spiders' webs and vice versa. The males paid more attention to females' presence than webs alone, still approaching females with full stomachs more often.

Read more at Discovery News